Resiliency of Bridges on the BOSFOLK Corridor
By Harry W. Shenton III and Peter Seymour
A report submitted to the University of Delaware University
Transportation Center (UD-UTC)
August 26, 2013
DISCLAIMER:
The contents of this report reflect the views of the authors, who
are responsible for the facts and the accuracy of the information
presented herein. This document is disseminated under the
sponsorship of the Department of Transportation University
Transportation Centers Program, in the interest of information
exchange. The U.S. Government assumes no liability for the
contents or use thereof.
UDUTC Final Report
Page i
Abstract
Built with a design life of 50-years, many of the bridges on the Boston to Norfolk (BOSFOLK)
corridor are nearing the end of their design life. Neglect, poor maintenance, and insufficient
funding have left many of them in very bad condition. As the bridges on the BOSFOLK corridor
near the end of their design life, one might ask, how resilient were the bridges on the corridor?
How did the bridges on I-95 perform compared to those not on the corridor? And what can be
learned from the BOSFOLK corridor about the durability and long-term performance of bridges?
The objective of the research presented was to investigate, assess, and document the historic
resiliency of bridges on the BOSFOLK corridor through a systematic investigation of historic data
from the National Bridge Inventory (NBI) database from the period 1992 through 2009.
Two different perspectives were considered in this study – the “macroview” perspective and
the “microview” perspective. The macroview approach used a very broad definition of the
corridor that included more than 78,000 bridges. The microview approach used a much more
narrowly defined view that included just under 38,000 bridges. In each case a database was
created that included bridges “on the corridor” and bridges “off the corridor.” Descriptive and
performance parameters were selected from the NBI and used to create databases that
covered the period 1992 through 2009. Results were analyzed and presented in the form of
timeline and column plots that show how the overall performance of the different inventories
performed over the 18 year period.
The macroview analysis revealed that the on-corridor inventory of bridges, while only slightly
fewer in number and older than the off-corridor inventory, accounted for more bridge roadway
area and was exposed to higher traffic volumes than the off-corridor inventory. However, by
most of the tangible performance measures, which includes sufficiency rating, postings, and
condition ratings, the on-corridor inventory performed better than the off-corridor inventory:
the operating and inventory ratings were similar for both inventories. Thus, while there was
more demand on the on-corridor inventory, the inventory performed better overall, than the
off-corridor inventory. Both inventories, however, either improved or remained about the same
during the 18 year period, indicating general overall improvement of the entire inventory over
time.
The microview analysis revealed that the on-corridor inventory of bridges was younger and
significantly smaller, but aging at a faster rate than the off-corridor inventory. The average
roadway area of the on-corridor bridges was substantially larger than that of the average offcorridor bridge; however, the total bridge roadway area was greater off of the corridor. As was
observed for the macroview, the traffic on the corridor was significantly higher than off of the
corridor. Implied with this higher traffic are more load cycles and more heavy load cycles on the
UDUTC Final Report
Page ii
corridor versus off of the corridor. However, by all of the tangible performance measures,
which includes sufficiency rating, postings, condition ratings, operating and inventory ratings,
the on-corridor inventory performed better than the off-corridor inventory. Thus, while there
was more demand on the on-corridor inventory, the inventory performed better overall, than
the off-corridor inventory. Some performance factors for the on-corridor inventory increased
over time, indicating a general overall improvement of the condition of the inventory, while
others decreased, indicating a general decline in performance.
UDUTC Final Report
Page iii
Table of Contents
1
2
3
4
5
Introduction ............................................................................................................................. 1
1.1
Background....................................................................................................................... 1
1.2
Literature Review ............................................................................................................. 3
1.3
Objective of the Research ................................................................................................ 5
1.4
Outline of the Report ....................................................................................................... 5
BOSFOLK Databases and Data Analysis ................................................................................... 7
2.1
The National Bridge Inventory ......................................................................................... 8
2.2
Selected NBI Data Items ................................................................................................... 8
2.3
Data Collection ............................................................................................................... 16
2.4
Analysis of Historical Bridge Performance ..................................................................... 19
Macroview Results................................................................................................................. 23
3.1
The Macroview BOSFOLK-NBI Corridor.......................................................................... 23
3.2
Creation of the Macroview Database ............................................................................ 27
3.3
Results of Performance Analysis .................................................................................... 28
3.4
Summary of Findings for Macroview Corridor ............................................................... 46
Microview Results.................................................................................................................. 51
4.1
The Microview BOSFOLK-NBI Corridor........................................................................... 51
4.2
Creation of the Microview Database ............................................................................. 55
4.3
Results of Performance Analysis .................................................................................... 57
4.4
Summary of Findings for Microview Corridor ................................................................ 75
Summary and Conclusions .................................................................................................... 79
Acknowledgements....................................................................................................................... 81
References .................................................................................................................................... 81
UDUTC Final Report
Page iv
List of Tables
Table 2.1 Bridges in BOSFOLK states, 2009 .................................................................................... 8
Table 2.2 Item 5 – Inventory Route (Recording, 1995)................................................................... 9
Table 2.3 Type codes for Item 70 – Bridge Posting ...................................................................... 14
Table 3.1 Number of bridges in macroview BOSFOLK-NBI database ........................................... 23
Table 3.2 Number of counties for on- and off-corridor macroview BOSFOLK database ............. 24
Table 3.3 Number of bridges on- and off- corridor for BOSFOLK macroview .............................. 26
Table 3.4 Blank entries in calculating roadway area of on-and off-corridor macroview bridges 30
Table 3.5 Blank entries in calculating roadway area of on- and off-corridor macroview posted
bridges........................................................................................................................................... 45
Table 3.6 Summary comparison of macroview results................................................................. 48
Table 4.1 Number of bridges in microview BOSFOLK-NBI database in 2009 ............................... 51
Table 4.2 Number of counties for microview BOSFOLK database in 2009................................... 53
Table 4.3 Number of bridges on- and off-corridor for BOSFOLK microview database in 2009 ... 55
Table 4.4 Blank entries in calculating roadway area of on-and off-corridor microview bridges . 59
Table 4.5 Blank entries in calculating roadway area of posted on-and off-corridor microview
bridges........................................................................................................................................... 74
Table 4.6 Summary comparison of microview results ................................................................. 77
UDUTC Final Report
Page v
List of Figures
Figure 2.1 Summary of sufficiency rating factors (Recording, 1995) ........................................... 16
Figure 2.2 Example of NBI bridge records in text file. .................................................................. 17
Figure 3.1 Map of selected counties in BOSFOLK macroview ...................................................... 25
Figure 3.2 Total number of macroview bridges on- and off-corridor .......................................... 28
Figure 3.3 Average age of macroview bridges on- and off-corridor ............................................ 29
Figure 3.4 Average roadway areas for macroview bridges on- and off-corridor ......................... 30
Figure 3.5 Estimated total roadway area values for macroview bridges on- and off-corridor .... 32
Figure 3.6 Average ADT values for macroview bridges on- and off-corridor ............................... 33
Figure 3.7 Average ADTT values for macroview bridges on- and off-corridor ............................. 34
Figure 3.8 Average sufficiency ratings for macroview bridges on- and off-corridor.................... 35
Figure 3.9 Percentage of macroview bridges with an operational posting (other than “A”) ...... 36
Figure 3.10 Percentage of macroview bridges posted “A” (Open, no restriction)....................... 37
Figure 3.11 Percentage of macroview bridges posted “P” (Posted for load) ............................... 38
Figure 3.12 Percentage of load postings (item 70) for macroview bridges on- and off-corridor 39
Figure 3.13 Average deck condition ratings for macroview bridges on- and off-corridor ........... 40
Figure 3.14 Average superstructure condition ratings for macroview bridges on- and offcorridor ......................................................................................................................................... 41
Figure 3.15 Average substructure condition ratings for macroview bridges on- and off-corridor
....................................................................................................................................................... 41
Figure 3.16 Average normalized operating ratings for macroview bridges on- and off-corridor 42
Figure 3.17 Average normalized inventory ratings for macroview bridges on- and off-corridor 43
Figure 3.18 Average posted roadway area for macroview bridges on- and off-corridor ............ 44
Figure 3.19 Estimated total posted roadway area for macroview bridges on- and off-corridor . 46
Figure 4.1 Map of selected counties in the BOSFOLK microview ................................................. 54
Figure 4.2 Total numbers of microview bridges on- and off-corridor .......................................... 57
Figure 4.3 Average ages of microview bridges on- and off-corridor ............................................ 58
Figure 4.4 Average roadway areas of microview bridges on- and off-corridor ........................... 59
Figure 4.5 Calculated total roadway area values of microview bridges on- and off-corridor...... 61
Figure 4.6 Average ADT values of microview bridges on- and off-corridor ................................. 62
Figure 4.7 Average ADTT values of microview bridges on- and off-corridor ............................... 63
Figure 4.8 Average sufficiency ratings of microview bridges on- and off-corridor ...................... 64
Figure 4.9 Percentages of microview bridges with an operational posting ................................. 65
Figure 4.10 Percentages of microview bridges posted “A” (Open, no restriction) ...................... 66
Figure 4.11 Percentages of microview bridges posted “P” (Posted for load) .............................. 67
Figure 4.12 Percentages of load postings of microview bridges on- and off-corridor ................. 68
Figure 4.13 Average deck condition ratings for microview bridges on- and off-corridor ............ 69
UDUTC Final Report
Page vi
Figure 4.14 Average superstructure condition ratings for microview bridges on- and off-corridor
....................................................................................................................................................... 70
Figure 4.15 Average substructure condition ratings for microview bridges on- and off-corridor70
Figure 4.16 Average normalized operating ratings of microview bridges on- and off-corridor .. 71
Figure 4.17 Average normalized inventory ratings of microview bridges on- and off-corridor .. 72
Figure 4.18 Average posted roadway areas of microview bridges on- and off-corridor ............. 73
Figure 4.19 Estimated total posted roadway areas of microview bridges on- and off-corridor .. 75
UDUTC Final Report
Page vii
1 Introduction
1.1 Background
The interstate highway system was authorized in 1956 by the Federal-Aid Highway Act. It
includes almost 43,000 miles of highway and thousands of bridges. One of the major northsouth routes of the system is Interstate-95 (I-95), which runs from Florida to Maine and covers
almost 2,000 miles. Interstate-95 is the backbone of the Boston, MA to Norfolk, VA, i.e., the
BOSFOLK transportation corridor. It is this corridor, and more specifically the bridges on the
corridor, that is the focus of this report.
Built with a design life of 50-years, many of the bridges on the BOSFOLK corridor are nearing
the end of their design life. Neglect, poor maintenance, and insufficient funding have left many
of them in very bad condition. In their recently released 2013 Report Card for America’s
Infrastructure, the American Society of Civil Engineers gave bridges in the U.S. a grade of “C+”.
This was the second highest grade awarded to any of the 16 infrastructure categories, but
nonetheless, indicates serious deficiencies in our nation’s bridge inventory. The cost to repair or
replace these bridges is staggering. Congress has in recent years authorized additional spending
that will go toward repairing or replacing some of the bridges on the BOSFOLK corridor.
As the bridges on the BOSFOLK corridor near the end of their design life, one might ask
•
How resilient were the bridges on the corridor?
•
How did the bridges on I-95 perform compared to those not on the corridor? Did they
perform better, worse, or about the same as bridges not on the corridor? If so, why?
•
What can be learned from the BOSFOLK corridor about the durability and long-term
performance of bridges?
The inventory of bridges on the corridor presents a unique opportunity to study the
performance of bridges and how the corridor may or may not have influenced their long-term
performance. The knowledge gained from this understanding may be used in the future to
develop better strategies for managing bridges in general, and more specifically, strategies for
managing a system of bridges on a major corridor.
When considering the corridor and the performance of bridges on it, there are a number of
reasons why bridges on the corridor may have performed differently. First, I-95 is the primary
north-south route for all commercial traffic in the mid-Atlantic and northeast regions. I-95
experiences some of the highest Average Daily Truck Traffic (ADTT) and highest loads of any
roads in the corridor. Fracture critical bridges and fatigue prone details are influenced by ADTT
UDUTC Final Report
Page 1
and load levels. The higher the ADTT and higher the loads, the shorter the life expectancy. Thus,
this can lead to faster deterioration and earlier repair.
Second, because there is such great demand to keep the interstate open and traffic moving,
states are more likely to focus their resources on these highways during heavy snow storms
than they are on secondary or tertiary roads. Bridges on I-95 in the BOSFOLK corridor are likely
to be exposed to more de-icing salts and more frequency plow runs, than bridges not on I-95.
All of which can lead to faster deterioration.
Finally, there may be other policies or operational factors that affect the performance of
bridges in the corridor. The correlations may be weak or even be unidentifiable, but could have
a positive or negative influence on performance.
When it comes time for maintenance, repair, or replacement, owners are more likely to
allocate limited funds and resources to the repair of bridges on the major highways than they
are for secondary or tertiary bridges to minimize the impact on the traveling public and
commerce. Or, they may be hesitant to proceed if it is going to mean major shutdowns or
detours. Thus they might delay the repair or attempt to find an alternative solution that doesn’t
require a shutdown.
Thus, while there are certainly greater demands placed on bridges on I-95, closer attention and
more resources are allocated to the maintenance, repair, and replacement of bridges on the
major highways. Thus the question arises, does the historical record suggest any difference in
the performance of bridges on the corridor (good or bad, better or worse), versus those off of
the corridor?
The National Bridge Inventory (NBI) database was created in 1967 in response to the Silver
River bridge collapse. Since that time states and bridge owners have been required to report to
the Federal Highway Administration, on an annual basis, information about all of the bridges in
their inventory. A single bridge record in the NBI provides quantitative and descriptive
information about the condition of the bridge, at the time of reporting. Thus, while the NBI was
not originally developed for studying the long-term performance of bridges, now more than 40
years old, the ensemble of annual database files contain within them historical data on the
performance of bridges in the U.S. Analyzed longitudinally over some years, the NBI data should
provide some information of how bridges on the BOSFOLK corridor performed, and how they
performed in comparison to bridges not on the corridor. The focus of this study was on
studying the performance of bridges in the BOSFOLK corridor, and comparing the performance
of bridges on I-95 versus those not on I-95. This was done by analyzing historic data from the
National Bridge Inventory (NBI) database.
UDUTC Final Report
Page 2
1.2 Literature Review
A number of studies have been conducted that used the National Bridge Inventory database as
a basis for examining the historical performance of bridges. Some of these studies have used
just one year of NBI data for a state or the country, and others have used multiple years of a
state or the country in their investigations. These are briefly described below.
Dunker and Rabbat (1990) used the NBI database to study the nation wide distribution of
bridge types and their performance, for bridges built between 1950 and 1987. They examined
the distribution of deficiencies in the 12 most common types of bridges. They noted that the
most common deficiency in interstate bridges is the deck, and in county bridges it was the
substructure. Also, that two of the three most common types of bridges, steel stringer and
timber stringer, have the highest percentage of deficiencies.
Starting in 2006, Farhey (2006, 2010, 2011, 2012, 2013) presented a series of five articles which
examined the historical performance of bridges in the US using the NBI, and presented a
framework for evaluating the performance of bridges. Using data from the 2004 NBI database,
Farhey (2006) examined the statistics for the number of bridges, number of SD bridges, and the
number of Functionally Obsolete (FO) bridges in the US. The study found that the average age
of SD bridges was 60 and the average age of FO bridges was 50, both below the expected 75
service life of bridges in the US. The rate of change of SD and FO bridges was insignificant.
In 2010, Farhey (2010) reported on the historical performance of bridges based on the type of
material (e.g., steel, concrete, timber, etc). The paper also introduced, for the first time, four
different performance indicators: “condition performance,” “durability performance,”
“longevity performance,” and “equivalent structural performance.” Condition performance was
defined as one minus the percentage of SD bridges in the inventory (i.e., the percentage of
Structurally Adequate (SA) bridges). Durability performance was defined to consider the
number of years before an average SA bridge becomes SD. Longevity performance was defined
to compensate bridges that have an average SD age higher than the 75 year service life. Finally,
the equivalent structural performance was a linear weighted combination of the other three
indicators. Using this approach the different material types were compared based on their
condition, durability, longevity and equivalent performance. The results showed that
aluminum/iron and some other materials showed considerably higher performance; concrete,
steel, and precast concrete were comparable; and wood and masonry were quite low.
The work presented in Farhey 2011, 2012, and 2013, were all very similar to the 2010 work with
the exception of how the bridge performance was compared. In all cases the condition,
durability, longevity, and equivalent indicators were computed. In 2011, Farhey (2011)
examined performance based on type of construction (e.g., slab, stringer, truss, etc). The
UDUTC Final Report
Page 3
results showed a stark contrast between relatively high condition performance and low
durability performance of almost all 23 types of construction. In 2012, Farhey (2012) examined
performance based on materials by bridge deck area. This was in comparison to the 2010 work
which compared material performance by number of bridges of a certain material type. The
results showed that steel, precast concrete, and concrete comprise nearly 99% of all of the
bridge area in the US and have an average SD age (42 years) significantly below the 75 year life
expectancy. Overall the equivalent performance by area were quite low, and lower than the
performance determined by number of bridges. Aluminum/iron and other materials showed
considerably higher performance. The final paper in the series, Farhey (2013), reports on a
similar analysis of bridge performance by structure type and bridge deck area. This was in
comparison to the 2011 work which compared construction type performance by number of
bridges. Similar results were found, where the equivalent performance by bridge area was
lower than is was by number of bridges.
Li and Burgueno (2010) used historical NBI data from Michigan along with soft computing
methods to develop predictive models for bridge performance. Their study was focused on
damage to bridge abutment walls. A number of different computing strategies were attempted,
all of which could be classified as either neural networks or fuzzy logic. It was shown that
reasonable deterioration curves could be developed based on these techniques.
Tabatabai, et al (2011) developed a reliability model for long-term management of bridges
decks in Wisconsin. The investigators used data from the 2005 NBI for Wisconsin as the input
for the model. The model was based on a hypertabastic accelerated failure time model. Results
showed that deck area, type of superstructure, and ADT are all important factors in the
reliability of bridge decks in Wisconsin.
Lee (2012) used the historical NBI database to examine nationwide trends in the number, area,
and material type of Structurally Deficient (SD) bridges in the US. The work was based on an
analysis of the data between 1990 and 2010. Lee concluded that the bridge most likely to be
found to be SD would be one that is 50 years old or older, of steel stringer construction with a
cast-in-place reinforced concrete deck, constructed of black reinforcing steel, simply-supported,
and be located in a rural area with an Average Daily Traffic (ADT) less than 10,000 vehicles.
To the best of the author’s knowledge, no prior studies have investigated the performance of a
major transportation corridor in the US, such as the BOSFOLK corridor, using the NBI data or by
other means. Nor have studies attempted to discern any difference in performance of bridges
that are on a major interstate or corridor, versus those that are not on the corridor.
UDUTC Final Report
Page 4
1.3 Objective of the Research
The objective of the proposed research was to investigate, assess, and document the historic
resiliency of bridges on the BOSFOLK corridor through a systematic investigation of historic data
from the National Bridge Inventory (NBI) database from the period 1992 through 2009. The
study examined the performance of bridges on the BOSFOLK corridor, and also compared that
to the performance of bridges off of the corridor. The investigation was carried out from two
different perspectives, (1) a “macroview” perspective which envisioned the BOSFOLK corridor
and it’s range of influence to be fairly broad, and (2) from a “microview” perspective which
envisioned the BOSFOLK corridor and it’s range of influence to be fairly narrowly defined by I95 and other major interstates in the northeast.
1.4 Outline of the Report
The remainder of the report is organized as follows. Chapter 2 describes the approach used to
gather the NBI data, create the databases, and analyze the historical data. Chapter 3 describes
the development of the “macroview” on-corridor and off-corridor databases and the results of
the analyses of the macroview historical data. Chapter 4 describes the development of the
“microview” on-corridor and off-corridor databases and the results of the analyses of the
microview historical data. Finally, Chapter 5 presents the summary and conclusions.
UDUTC Final Report
Page 5
UDUTC Final Report
Page 6
2 BOSFOLK Databases and Data Analysis
The purpose of this chapter is to describe the collection, organization, and analysis of historic
bridge performance data for this project. The FHWA (Federal Highway Administration)
maintains a database of information on all bridges in the United States that are 20 feet or more
in length, called National Bridge Inventory. NBI data, beginning from 1992, are publicly available
from the FHWA website (http://www.fhwa.dot.gov/bridge/nbi.htm). The data are contained in
ASCII files, organized by state and year. Each line or “record” in a file represents one bridge in
the state for that year. There are also records for all roads and highways that pass under a
bridge; these are referred to as “under” records. Thus, the total number of records in a given
state file will be greater than the actual number of bridges in the state for that year. The
number of records will also vary from year to year as new bridges are constructed and others
are taken out of service and not replaced.
The first step in the process of analyzing the performance of bridges on the BOSFOLK corridor
was to create the BOSFOLK databases. This required several steps. First, state files were
downloaded only for the states that carry the BOSFOLK corridor. Next, using a specific
definition of the corridor the records for bridges in the corridor were extracted from the state
files. The physical extent of the corridor was determined using road maps that identify highway
routes and county boundaries (described later). Coding parameters were used to determine
what bridges to extract from the state files. Examples include the county in which a bridge is
located, a numeric interstate highway identifying code, and the length of the bridge. The
BOSFOLK-only records were then assembled to form a single entity, called the BOSFOLK-NBI
database, containing 18 years of data.
To the best of the author’s knowledge there is no unique definition for the BOSFOLK corridor –
it simply extends from Boston, MA to Norfolk, VA, with I-95 as its backbone. The reach of the
corridor, as one moves away from I-95, however, is very subjective: is it a few miles, tens of
miles, or hundreds of miles? This question arose in the process of developing the BOSFOLK
database. Since it is somewhat subjective, the approach taken here was to consider two distinct
perspectives of the corridor - a “macroview” and a “microview”. The first is the larger of the
two and includes many more square miles along and perpendicular to the path of I-95. For this
view most states bordering the Atlantic Ocean had all of their counties included as part of the
corridor. The microview was defined more explicitly by the path of interstate 95 and its major
interstate tributaries. The two views are described in more detail later. To study if the longterm performance of a bridge was affected by whether it is “on” the corridor, versus “off” the
corridor, the two databases were then separated into groups of bridges that are “on-corridor”
and those that are “off-corridor”. Thus, in the end there are four separate databases:
macroview on-corridor, macroview off-corridor, microview on-corridor, and microview offcorridor.
UDUTC Final Report
Page 7
2.1 The National Bridge Inventory
NBI data is currently available to the public on the FHWA website
(http://www.fhwa.dot.gov/bridge/nbi.htm) for the years 1992 to 2012. The project utilized
data for the 18-year period from 1992 to 2009; this represents the data available at the time
when the BOSFOLK database was created (earlier years can be obtained by special request from
FHWA, however, the 18 years available at the time the data was gathered was considered
sufficient for the purposes of this research project as it captures the most recent data and data
from the later years of the bridge’s life, which is presumably when a bridge would deteriorate
fastest). The path of Interstate-95 between Boston, MA and Norfolk, VA determined the states
and the District of Columbia that were used to create the BOSFOLK corridor databases. These
include: New Hampshire, Massachusetts, Rhode Island, Connecticut, New York, New Jersey,
Pennsylvania, Delaware, Maryland, District of Columbia, and Virginia. Presented in Table 2.1 is
the total number of bridges in each of these states in 2009, excluding any bridges less than 20
feet in length 1.
Table 2.1 Bridges in BOSFOLK states, 2009
State
New Hampshire
Massachusetts
Rhode Island
Connecticut
New York
New Jersey
Pennsylvania
Delaware
Maryland
District of Columbia
Virginia
Total
No. of Bridges
2,509
5,043
768
4,187
17,375
6,486
22,313
862
5,205
246
13,537
78,531
One can see that the total number of bridges to begin with was just over 78,500, with the most
coming from Pennsylvania and the fewest from DC.
2.2 Selected NBI Data Items
An NBI record is divided into 117 unique data items that characterize a bridge in the inventory.
Some data items are descriptive, such as bridge location, orientation, and size. Other data
items can be described as performance-related, i.e., in some way characterize the bridge’s
1
States are not required to report information on bridges less than 20 ft in length, however, some do. Therefore,
to be consistent any bridges in a state’s inventory less than 20 ft in length were excluded.
UDUTC Final Report
Page 8
structural condition. The FHWA report “Recording and Coding Guide for the Structure
Inventory and Appraisal of the Nation’s Bridges” (Recording, 1995), contains explanations of the
data items and the format of the bridge record. Each bridge record is a single string of alpha
numeric characters. Developed in the 60’s to be read by a computer, there is a specific format
of the string with individual coding items embedded in it.
To minimize storage requirements not all 117 items were included in the BOSFOLK database.
Some items were deemed not relevant to studying the resiliency of the bridges and therefore
could be excluded. Also, “under” records were excluded entirely as these also were deemed
not relevant to the objectives of the project.
2.2.1 Descriptive Parameters
In this section the descriptive parameters used in creating the BOSFOLK-NBI database are
identified and described.
Item 3 – County (Parish) Code: The Federal Information Processing Standards (FIPS) codes are
used to identify the counties in all states. These codes are determined from the current census.
For each bridge record, the county codes show in which county that bridge resides. The FHWA
obtains these codes from the National Institute of Standards and Technology website
(http://www.itl.nist.gov/fipspubs/co-codes/states.htm).
The next two items, Item 5A and Item 5D, are two segments of a five character code that
inventories the highway routes that are carried or that coincide with a structure. The remaining
unused digits of Item 5 still appear in the final databases as part of bridges’ records, but only
items 5A and 5D were used to sort the BOSFOLK records for this project. For completeness, all
5 segments are outlined as follows:
Table 2.2 Item 5 – Inventory Route (Recording, 1995)
Segment
5A
5B
5C
5D
5E
Title of Segment
Record Type
Route Signing Prefix
Designated Level of Service
Route Number
Directional Suffix
Length
1 digit
1 digit
1 digit
5 digits
1 digit
Item 5A – Record Type: The NBI contains two types of records for bridges: “on” (type code =
“1”), meaning the bridge carries that highway route across its span, and “under” (type code =
“2”), meaning that route passes beneath the span and through the bridge’s open space. It
follows that each structure carrying highway traffic must have a record signifying that route to
UDUTC Final Report
Page 9
be “on” the structure. Choosing only records with 5A type code “1” eliminated the “under”
bridge records.
Item 5D – Route Number: This 5 digit code identifies the route number of the inventory route.
For example, Interstate-95 has the type code “00095,” and Delaware State Route DE-273 is
“00273.” This item simplified the identification of a path or any number of paths when creating
and sorting the BOSFOLK database. In this way, it was useful to isolate bridges carrying
Interstate-95, or exclude other routes.
Below are examples of item 5 coding:
Route Name
I-95, on
U.S. 1N bypass, on
I-676W, under
5A
1
1
2
5B
1
2
1
5C
1
3
1
5D
00095
00001
00676
5E
0
1
4
Record Code
111000950
123000011
211006764
Item 6A – Features Intersected: This 25 character item is a text description of the features
intersected by the structure. The names of features are given, along with any additional
identifiers the route may have. This descriptive item was used often to determine what other
routes of interest coincided with the path of Interstate-95.
Below are examples of item 6A coding:
Features Intersected
ROOSELT.PK.NAVY YARD;I95
SCHUYLKILL RIVER,RR,ROAD
CHRISTINA RIVER, N/S RR
Item 7 – Facility Carried by Structure: This 18 character item is a text description of the use “on”
the structure. This descriptive item was useful in identifying the route a bridge carried, and was
another way of checking if the records selected corresponded to that which was intended.
Below are examples of item 7 coding:
Facility Carried by Structure
VIETNAM VET MEM HY
I95 NB/JFK MEM HGY
Interstate-95 NBL
Item 9 – Location: This 25 character item is a text description of the bridge’s location. FHWA
recommends that the structure’s location be keyed to a distinguishable feature. The bridge
UDUTC Final Report
Page 10
location is usually indicated by the distance and direction from said feature. This item was used
to “place” a bridge (note that NBI records also include the longitude and latitude of a bridge;
however, upon examination some of these coordinates were found to be inaccurate and
therefore not a reliable means of locating a bridge).
Below are examples of item 9 coding:
Location of Structure
.16 KM.SW GRT PLAIN AVE
.1 MI.SW OF GRT PLAIN AVE
.32 KM SLY RTS 20 & 128
The next two items, Item 49 – Structure Length and Item 51 – Bridge Roadway Width, Curb-toCurb, are descriptive items used to calculate the roadway area carried by the bridge. Both
items report lengths to tenths of a meter. The area (to be used later) is found by multiplying
the structure length by the roadway width. This number provided the roadway area measure in
units of square meters.
Item 49 – Structure Length: The length of a structure, defined by the length of roadway that is
supported on the structure. This length is measured in meters, to the nearest tenth of a meter,
and it is coded as follows: XXXXX.X meters.
Below are examples of item 49 coding:
Structure Length
1,372.5 meters
2,490.2 meters
1,945.0 meters
Record Code
013725
024902
019450
Item 51 – Bridge Roadway Width, Curb-to-Curb: This is the measure of the distance between
curbs and rails on a structure’s roadway. This is not the same as the out-to-out deck width,
because Item 51 disregards roadway covered by parapets, non-mountable medians, nonmountable curbs, sidewalks, rails, and other features (such as flared areas of ramps). The width
of mountable medians is included in this measurement. This width is measured in meters, to
the nearest tenth of a meter, and it is coded as follows: XXX.X meters.
Below are examples of item 51 coding:
Roadway Width
29.9 meters
23.7 meters
UDUTC Final Report
Record Code
0299
0237
Page 11
26.8 meters
0268
2.2.2 Performance Parameters
In this section the performance parameters used in creating the BOSFOLK-NBI database are
described.
Item 27 – Year Built: This item indicates the year in which construction of the structure was
completed. The year built was used to determine the age of the bridge.
Item 29 – Average Daily Traffic: This item shows the average daily traffic (ADT) for the inventory
route identified in Item 5D. The ADT vehicle count includes trucks. Trucks are identified as a
percentage of the ADT by Item 109 – Average Daily Truck Traffic. This parameter provides a
quantitative measure of the “use” or traffic demand on the bridge.
Item 41 – Structure Open, Posted, or Closed to Traffic: This item describes the operational status
of a bridge, using one of 8 type codes, each designated by a letter. These codes are listed as
follows:
1.
2.
3.
4.
5.
6.
7.
8.
“A” - Open, no restrictions
“B” - Open, posting recommended but not legally implemented (all signs not in place
or not correctly implemented
“D” - Open, would be posted or closed except for temporary shoring, etc. to allow for
unrestricted traffic
“E” - Open, temporary structure in place to carry legal loads while original structure is
closed and awaiting replacement or rehabilitation
“G” - New structure not yet open to traffic
“K” - Bridge closed to all traffic
“P” - Posted for load (may include other restrictions such as temporary bridges which
are load posted)
“R” - Posted for other load-capacity restriction
The type code is determined by the governing agency’s posting procedures, and not by the
bridge’s operating stress level. Type code “P” generally indicates that a structure cannot be
loaded to its operating stress level. However, this item may indicate that a bridge is posted, but
Item 70 – Bridge Posting may show that posting is not required. Item 70 is based on the
operating stress level, and does not account for agencies’ posting procedures.
Items 58-62 Structure Condition Ratings: are numeric Condition Ratings that range from a high
of 9, for a component in excellent condition, to a low of 0, for a failed component. Quantitative,
but subjective in their assignment, these parameters are the key ratings that describe the
UDUTC Final Report
Page 12
condition of the bridge, as assigned by the bridge inspector. Thus, they are key performance
indicators. The items are:
•
•
•
•
•
Item 58 – Deck
Item 59 – Superstructure
Item 60 – Substructure
Item 61 – Channel/Channel Protection
Item 62 – Culverts
Note that a single numeric value is provided for each of the three major structural components
of a typical bridge: the substructure, the superstructure, and the deck. This is true regardless of
whether the bridge in 20 ft in length or 2000 ft in length, e.g., one value is assigned to deck
condition regardless of the length or square area of deck on the bridge.
The next two data items, Item 64 – Operating Rating and Item 66 – Inventory Rating, are
classified as capacity ratings. Capacity ratings are a quantitative indication of the load level to
which the bridge may be subjected under different conditions, and are determined by
conducting an analytical load rating of the bridge. The MS loading method is used to determine
the operating rating; these metric loadings represent an equivalent HS load level. Item 64
represents the mass of the entire vehicle, measured in metric tons to the nearest tenth of a
ton. These 3-digit items are coded as follows: XX.X metric tons.
Presented below are examples of the codings:
HS Load
HS20
HS15
MS Load
MS18
MS13.5
Metric Tons Record Code
32.4
324
24.3
243
Item 64 – Operating Rating: This capacity rating indicates the absolute maximum permissible
load level to which the structure may be subjected for the vehicle type used to determine the
rating. The operating rating is the upper limit of what “one-time” loads the bridge may
experience. Operating rating is related to Item 70 – Bridge Posting. A bridge’s posting for load
typically expresses the operating rating’s value as a percentage less than, greater than, or equal
to the presiding state’s legal load.
Item 66 – Inventory Rating: This capacity rating indicates the load level which may safely utilize
the structure for an indefinite period of time. The inventory rating represents a load level that
the bridge may sustain for long-term, “steady state” use. The bridge may experience this load
level many times without deleterious effect. It is some percentage less than the bridge’s
operating rating.
UDUTC Final Report
Page 13
Item 70 – Bridge Posting: This item describes the bridge load capacity in comparison to the
state legal load. The National Bridge Inspection Standards (NBIS) require the posting of load
limits if the state-defined maximum legal load exceeds the operating rating of the bridge. The
item’s type codes are listed in Table 2.3.
Table 2.3 Type codes for Item 70 – Bridge Posting
Type Code
5
4
3
2
1
0
Relationship of Operating Rating to Maximum Legal Load
Equal to or above legal loads
0.1 – 9.9% below
10.0 – 19.9% below
20.0 – 29.9% below
30.0 – 39.9% below
More than 39.9% below legal loads
An item code of “2” (20 – 29.9% below) means that the operating rating may be
from 20 to nearly 30 percent below the state-defined maximum legal load.
Bridges are required to be posted if the type code is anything other than “5”
(equal to or above legal loads).
Item 109 – Average Daily Truck Traffic (ADTT): This 2 digit item describes the occurrence of
trucks on a given route. The ADTT is reported as a percentage of the ADT (item 29). Item 109
defines the percent as a whole number.
Below are examples of item 109 coding:
Trucks as Pct. of ADT
12%
7%
26.9%
Record Code
12
07
27
Item SR – Sufficiency Rating: The Sufficiency Rating (SR) is calculated by the processes detailed
in Appendix B of the Recording and Coding Guide (Recording, 1995), and results in a percentage
between 0 and 100 that is indicative of a bridge’s sufficiency to remain in service. The
percentage is calculated to one decimal place.
Below are examples of item SR coding:
Sufficiency Rating
100.0
96.7
36.8
UDUTC Final Report
Record Code
1000
0967
0368
Page 14
Appendix B of the Recording and Coding Guide provides the procedure and formulae to
perform these calculations. An outline of the sufficiency rating factors is provided in Figure 2-1.
One final performance parameter that is not reported in the NBI but was calculated from NBI
data is roadway area.
Roadway Area: Roadway area is not a specific entry in NBI record item; however, it serves as an
important performance parameter in evaluating bridge resilience. The bridge roadway area
was calculated by multiplying the Structure Length (item 49) by the Bridge Roadway Width
(item 51).
Presented below are examples of roadway area:
Structure Length
2,490.2 meters
1,574.9 meters
1,945.0 meters
UDUTC Final Report
x
x
x
Bridges Roadway Width
23.7 meters
29.3 meters
26.8 meters
=
=
=
Roadway Area
59,017.7 meters2
46,144.6 meters2
52,126.0 meters2
Page 15
Figure 2.1 Summary of sufficiency rating factors (Recording, 1995)
2.3 Data Collection
2.3.1 Downloading records
Multiple steps were necessary to collect the data. The NBI data are organized by state and by
year and are available for download from the FHWA
(http://www.fhwa.dot.gov/bridge/nbi.htm). The files were downloaded as text files containing
alphanumeric characters. Each row of letters and numbers is structured to match the required
FHWA coding guidelines. The coding guide explicitly defines the format of the records; every
data item is assigned a position, length, and type in the record. Figure 2.2 shows an example of
a NBI text file.
UDUTC Final Report
Page 16
Figure 2.2 Example of NBI bridge records in text file.
2.3.2 Importing into Microsoft Access
The BOSFOLK-NBI database was first created in Microsoft Access. Access is well suited to
handle the many bridge records necessary for analyzing the BOSFOLK corridor. The FHWA files
were downloaded and saved as text in the same format and with the same name as used by the
FHWA (the state and year the data were collected). To create the database the state files were
imported into Access using an import specification defined in accordance with the Recording
and Coding Guide’s format. Each Access table of records had 117 columns, one for each data
item. Each year of each state’s data was imported into Access and saved as a separate table. In
the end each state’s data was saved in a unique Access database file.
2.3.3 Sorting the NBI Data
Once in Access a state’s NBI bridge file could be sorted to exclude records that were not to
become part of the BOSFOLK database. The records were filtered by selecting criteria for each
data item. This sorting action was performed using an Access “query,” which is a feature that
can simultaneously filter the records using criteria for multiple data items. NBI records were
most commonly sorted using data items Item 3 – County (Parish) Code, and Item 5A – Record
Type. These items were most useful for extracting BOSFOLK-related records because all bridges
contained within a county could be extracted at one time. Identifying the bridges located
within any given county allowed the selection of bridges geographically on or near the BOSFOLK
corridor. Records of bridges outside the influence of the BOSFOLK corridor were excluded.
UDUTC Final Report
Page 17
Likewise, by filtering on item 5A=”1” only actual bridge records would be included and any
“under” records would be excluded from the database.
Sorting using county and record type ensured that the records isolated using the query were
both the correct type of record and in the desired region. The number of counties included in
the BOSFOLK database was determined by how far the influence of the corridor extended
beyond Interstate-95, which formed the corridor’s “spine.” The most definitive way to select
the counties for the macroview and microview BOSFOLK databases was to use road atlases.
These road maps featured each state’s highway routes and county boundaries. Once the
desired highway routes were located on the maps, the counties through which these highways
passed were identified. Next, the county codes were identified using the FIPS data available
from FHWA; each county has a unique 3-digit code that identified it by name. After each state’s
county codes were collected, the bridge records corresponding to those selected counties were
identified in the query. Then these records were extracted from the full NBI state databases
and transferred into the BOSFOLK database.
Structure Length (item 49) also played a role in creating the BOSFOLK database. The National
Bridge Inspection Standards (NBIS) stipulate the collection of data from bridge inspections
every two years, for bridges spanning 20 feet or more. Records for bridges spanning less than
20 feet do exist in the NBI, but they do not need to be inspected every 2 years. The BOSFOLK
database contains records only for bridges with spans greater than 20 feet (6.1 meters). This
was done by excluding any records with a structure length was less than 6.1 meters.
Databases of individual states’ records were created based on the filtering criteria. Each state’s
tables were organized in the same way they were by the FHWA: by state and year. Each state
now had its own database containing 18 tables of records, one table for each of the 18 years of
bridge data. Then the tables of state records were stitched together in succession to create the
BOSFOLK database. This database now contained records for all the bridges on the BOSFOLK
corridor, and organized by the year for which the data were submitted. The 18 tables in the
BOSFOLK databases contained only those bridge records pertinent to the BOSFOLK corridor.
These databases were then further filtered to create the macroview on- and off-corridor
databases, and the microview on- and off-corridor databases. These are described in more
detail in Chapter 3 and 4, respectively.
2.3.4 Transfer to Excel
Because Microsoft Excel is better suited to performing calculations, statistical analyses, and
plotting of data, the databases were then imported into Excel. In addition to the bridge
records, each spreadsheet had the results of various calculations used to “mine” the data for
trends. The Excel files typically contained data for an entire state, with the file’s individual
UDUTC Final Report
Page 18
sheets organized by year. New columns were added as necessary for the calculations on one or
more data items and helped form the basis for the charts.
Because of the large amounts of data, some of the Excel files became too large to handle
efficiently. Excel files sizes greater than 530 Mb of disk space rendered the program
unresponsive. This problem was observed when analyzing the complete records for the
BOLSFOLK corridor. This problem was solved by compiling results one year at a time, instead of
handling all 18 years’ worth of records at once. Each year’s resulting calculations were then
copied to a separate Excel file where only the results of each year’s calculations were stored.
Graphs were then created based on these compiled results.
2.4 Analysis of Historical Bridge Performance
Presented below is a discussion of how the data was analyzed to assess the performance of the
bridges on the corridor. Statistical analyses were done for selected data items so that historical
trends in bridge performance could be studied. Data in the NBI is organized by the year in
which the data was submitted to the FHWA. This made it logical to group the records by year
and helped identify trends in historic bridge performance. Results were visually analyzed by
displaying the data as either a line plot or a column plot, depending on the type of data. It was
common to calculate the mean and standard deviation for a data set, and to note the maximum
and minimum values observed.
The data items used to evaluate bridge performance for each year, and the types of statistical
analysis used for each item, are detailed in the following list:
Number of Bridges: timeline plot of the total number of bridges in a year
Age: timeline plot of the average age of the bridges
Roadway Area: – timeline plot of the average bridge roadway area
Total roadway area is a useful parameter to know when examining the performance of a large
group of bridges. The roadway area of each bridge was calculated by multiplying the Structure
Length (item 49) by the Bridge Roadway Width, Curb-to-Curb (item 51). With this calculated,
the total roadway area could have been calculated by simply summing the individual bridge
areas. However, it was discovered that some NBI records were missing either item 49 or item
51, which precluded calculating the roadway area of all bridges in the database, and therefore
also an estimate of the total roadway area. A method was developed to estimate the total
roadway area, which was to multiply the average roadway area obtained from the inventory of
bridges for which complete data was available, by the total number of bridges. Provided the
average roadway area was representative of the entire population (i.e., based on a reasonable
fraction of the total number of bridges in the database), the estimated total roadway area could
UDUTC Final Report
Page 19
be assumed to be valid. The same process was used to estimate the total roadway area of
posted bridges, by multiplying the average roadway area of posted bridges by the total number
of posted bridges. These calculations made it possible to study the influence of roadway area.
Estimated Total Roadway Area: timeline plot of the estimated total roadway areas, accounting
for missing data for all bridges
Average Daily Traffic: timeline plot of the average daily traffic
Average Daily Truck Traffic: timeline plot of the average daily truck traffic
Sufficiency Rating: timeline plot of the average sufficiency rating of the bridges in the inventory
The operational status (item 41) assigns one of 8 letter type codes to describe a bridge’s
availability for use. Two of these 8 codes were helpful in determining bridge performance: “A”
(Open, no restrictions) and “P” (Posted for load). A higher percentage of bridges designated “P”
indicates less carrying capacity than the state legal limit. The other 6 codes also indicate some
type of situation of limitation that precludes an “A” designation. This information was used to
generate 3 column plots to study bridge operational status: the percentage of total bridges that
are designated any letter other than “A,” the percentage of total bridges designated “A,” and
the percentage of total bridges designated “P.” High percentages of “A” and low percentages
of “P” indicated more optimal bridge performance.
Operational Status: various column plots of percentage occurrence of item 41 codings
Bridge Posting: column plot of percentage of bridges posted for load
Condition Ratings: – timeline plot of the average deck, superstructure, and substructure
condition ratings.
The operating and inventory ratings measure a bridge’s load carrying capacity in metric tons.
These values were normalized by the MS18 design truck load of 32.2 metric tons. Values
greater than “1” are a satisfactory rating, values less than “1” are an unsatisfactory rating
indicating the bridge cannot carry the legal load.
Operating Rating: timeline plot of the average normalized operating rating of the inventory.
Inventory Rating: timeline plot of the average normalized inventory rating of the inventory.
Posted Roadway Area: timeline plot of the average posted roadway area.
Estimated Total Posted Roadway Area: timeline plot of the estimated total posted roadway
area.
UDUTC Final Report
Page 20
The results of these statistical analyses were graphed to identify trends over the 18 year period
of available data. These analyses created a profile of historic bridge performance for each
state. After results were generated for individual states’ performance, the records and analyses
were compiled to produce a synopsis of performance for the entire corridor. Historic
performance of the corridor could be studied to identify patterns.
UDUTC Final Report
Page 21
UDUTC Final Report
Page 22
3 Macroview Results
The Macroview BOSFOLK-NBI database was the first of these two methods used to study the
resilience of bridges on the corridor. This chapter details the approach used to define the
macroview version of the corridor, the steps to create the macroview database, and the results
of analyzing the performance parameters. The macroview database “painted with a broad
brush” to define the physical extent of the corridor. The proximity of states’ counties to the
BOSFOLK corridor determined whether the bridges were “on” the corridor or “off” the corridor.
3.1 The Macroview BOSFOLK-NBI Corridor
3.1.1 Defining the Macroview Corridor
The path of Interstate-95 determined which states were included as part of the BOSFOLK
corridor. The macroview database was based on the list of 11 states and DC, between Boston
and Norfolk which I95 passes through. Table 3.1 shows the number of bridges in each state on
the macroview BOSFOLK corridor in 2009, the total number of bridges in the state, and the
percentage of the state total that was included in the macroview database. This highlights the
fact that the macroview is a very inclusive visualization of the corridor.
Table 3.1 Number of bridges in macroview BOSFOLK-NBI database
State
New Hampshire
Massachusetts
Rhode Island
Connecticut
New York
New Jersey
Pennsylvania
Delaware
Maryland
District of Columbia
Virginia
Total
Bridges in Macroview
2,505
5,043
768
4,187
17,372
6,486
22,283
862
5,149
246
13,528
78,429
Total Bridges in State
2,509
5,043
768
4,187
17,375
6,486
22,313
862
5,205
246
13,537
78,531
% of State Total
99.8
100
100
100
100
100
99.9
100
98.9
100
99.9
99.9
The database contained all or nearly all the bridges in each state that carried the corridor. This
was done to investigate what effect the BOSFOLK corridor may have on bridge performance at
some distance away from I-95.
UDUTC Final Report
Page 23
3.1.2 Classification of Bridges: On-corridor and Off-corridor
The macroview database bridge records were split into two categories. The first contained
records for bridges that were in close proximity to the path of the BOSFOLK corridor; these
were defined as “on-corridor” bridges. The second category defined bridges located outside
the influence zone of the BOSFOLK corridor; these were defined as the “off-corridor” bridges.
These two paired databases were titled “Macroview On-Corridor” and “Macroview OffCorridor.” In this way, it was possible to understand the behavior of bridges on the corridor
versus those off the corridor. Each subset of the macroview was studied individually, and the
results of these analyses were compared.
3.1.3 Selection of Counties and Bridges in the Macroview
A method was developed to define the region covered by the macroview definition of the
BOSFOLK corridor. Maps were obtained that showed both the major highway routes and the
boundaries of counties in selected BOSFOLK states. The path of I-95 was identified between
Boston and Norfolk. The boundary of the BOSFOLK corridor was extended, from the path of I95 outward through several counties in each state. Figure 3.1 shows the range of the
macroview organization scheme for the BOSFOLK corridor. The map was based on the county
boundaries of states carrying the BOSFOLK corridor. The counties highlighted in blue comprise
the on-corridor database, the counties highlighted in orange comprise the off-corridor
database.
Macroview bridges were selected based on a counties’ proximity to the BOSFOLK corridor. This
dictated that some states would contribute all of their counties to being on-corridor. Most of
the states bordering the Atlantic Ocean contributed all their counties to the path of the
BOSFOLK corridor. Larger states contributed smaller percentages of their counties, because
their borders typically extended farther from the path of I-95. Table 3.2 shows the number of
counties in each state that were classified on- and off-corridor in 2009. The percentage of
counties classified as on-corridor was calculated as well. This gave an understanding of the
interstate routes’ influence in the macroview definition of the BOSFOLK corridor.
Table 3.2 Number of counties for on- and off-corridor macroview BOSFOLK database
State
New Hampshire
Massachusetts
Rhode Island
Connecticut
New York
New Jersey
Pennsylvania
Delaware
UDUTC Final Report
Counties On-Corridor Counties Off-Corridor % On-Corridor
3
7
30
14
0
100
5
0
100
8
0
100
12
50
19.35
21
0
100
10
57
14.92
3
0
100
Page 24
State
Maryland
District of Columbia
Virginia
Total
Counties On-Corridor Counties Off-Corridor % On-Corridor
21
3
87.5
1
0
100
56
77
42.10
154
194
44.25
The composition of the macroview databases depended largely on the location of counties
within a state. Sometimes a significant portion of a state’s counties were included in the
macroview BOSFOLK corridor. Other states contributed less of their counties.
Figure 3.1 Map of selected counties in BOSFOLK macroview
UDUTC Final Report
Page 25
The selection of bridges for these databases was often dictated by the geometry of states’
boundaries. A state that was “tall” (i.e., its north and south borders extended proportionally
farther than it did east and west) had more counties in the influence zone of the principal
north-south interstate routes around I-95. Examples of this were New Jersey and Rhode Island.
Though different in size, the 2 states had a similar north-south orientation for the path of I-95.
This resulted in all the counties in New Jersey and Rhode Island being on-corridor. A total of 5
states and the sole district area (MA, RI, CT, NJ, DE, and DC) contributed all their counties to the
macroview. Other states had less of their counties on-corridor, such as New York and
Pennsylvania. These states carried I-95 through a small number of counties along their eastern
borders, and both states’ borders extended far west of I-95. The western counties were not
influenced by the BOSFOLK corridor’s interstate highways. This determined that most of these
states’ counties be classified as off-corridor.
Table 3.3 shows the number of bridges that were on-corridor and off-corridor for each state on
the macroview corridor in 2009. The percentage of all the states’ bridges that were on-corridor
is also listed.
Table 3.3 Number of bridges on- and off- corridor for BOSFOLK macroview
State
Bridges On-Corridor
Bridges Off-Corridor % On-Corridor
New Hampshire
868
1,637
34.65
Massachusetts
5,043
0
100
Rhode Island
768
0
100
Connecticut
4,187
0
100
New York
4,027
13,345
23.18
New Jersey
6,486
0
100
Pennsylvania
5,569
16,714
24.99
Delaware
862
0
100
Maryland
4,485
664
87.1
District of Columbia
246
0
100
Virginia
5,292
8,236
39.11
Total for Macroview
37,833
40,596
48.24
Note that approximately 44% of all counties were defined as on-corridor, and just over 48% of
the bridges in the macroview database were on-corridor.
Note that while only 15% and 20% of the counties in PA and NY, respectively, were included in
the database, almost 25% of the bridges in these two states were included. This illustrates the
high density of bridge in the eastern edges of these two states that are part of the corridor. The
macroview definition accounted for a higher number of bridges nearer the major interstate
routes. This increase in density was because of the counties’ proximity to bridges on the
UDUTC Final Report
Page 26
BOSFOLK interstate highways. This justified the selection of counties and bridges used to build
the macroview.
3.2 Creation of the Macroview Database
The process for creating the macroview on-corridor and macroview off-corridor databases was
as described in Chapter 2. Specific details are outlined below.
3.2.1 Creation of Macroview-Specific State Databases
The most important set of changes made to the macroview databases was the distribution of
records based on their state counties. The bridges had to be organized according to the oncorridor and off-corridor county selections detailed in Table 3.2 and Figure 3.1. This was done
using the Federal Information Processing Standards (FIPS) codes, which assigned a 3-digit code
to every county or specially designated area in a state. Some urban areas in Virginia and
Maryland were designated independent cities, but most BOSFOLK states used counties to
apportion their lands. The limits of the on-corridor and off-corridor macroview databases were
defined by states’ counties. The names of the counties in each group were identified and were
paired to their corresponding FIPS codes. The records in the states’ Access databases were split
according to the counties defined as on- and off-corridor. These records were used to create
new databases of macroview records.
3.2.2 Transferring Access Tables to Excel Files
The macroview databases of records were transferred to Excel files. These files kept the same
organization scheme of separate files for on-corridor records and off-corridor records. The
macroview database files were identical to the files created to individually analyze the states’
behaviors. Each file contained 18 spreadsheets, one for each year’s worth of bridges records.
Performance data was analyzed using columns of calculations added to the trailing edge of each
year’s data. Results of the yearly statistical analyses were compiled in a spreadsheet, which
was used to generate plots of the performance data. The files were organized by state and for
which part of the macroview database they accounted. These on- and off-corridor state files
were then compiled to create two files which contained a complete list of macroview bridges
records. This was done by copying the bridge records in the on- and off-corridor state files and
then pasting them into their corresponding macroview files. Note that the two-letter code of
“BF” was used to signify the BOSFOLK database bridges. This was done to maintain consistency
with the FHWA’s use of two-letter state codes (e.g.: DE for Delaware, PA for Pennsylvania, etc.).
3.2.3 Organization of Macroview Excel Files
There was too much information (i.e., too many bridges records) pertinent to the macroview
database for one Excel file to handle. The size of the Excel files became prohibitively large for
analyzing the data; consequently, the files had to be split into smaller files for analysis. This
necessary reorganization of the BOSFOLK records did not affect the analyses performed to
UDUTC Final Report
Page 27
determine performance trends for the bridges. Instead of one file containing all 18 years’ data,
the macroview analysis was organized into 4 separate files: 3 contained the records and
statistical analyses, and 1 contained the aggregate statistical analysis and plots of historic data.
The 3 files that held the records and results of yearly analysis were created by dividing the
database into 6-year periods for 1992-1997, 1998-2003, and 2004-2009. The final files
contained the compiled records and corresponding analyses for the total 18 years’ worth of
bridge records.
3.3 Results of Performance Analysis
Presented in this section are the results of the analyses of the data from the macroview
databases.
3.3.1 Number of Bridges
The on- and off-corridor macroview databases were not the same size. Figure 3.2 shows the
total number of bridges in the macroview on-corridor and off-corridor databases.
Number of Bridges, BF Bridges
42,000
41,000
Number of Bridges
40,000
39,000
38,000
37,000
36,000
35,000
No. of BF Bridges off corridor
34,000
No. of BF Bridges on corridor
33,000
32,000
92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09
Year
Figure 3.2 Total number of macroview bridges on- and off-corridor
The number of off-corridor bridges was always greater than the number of bridges on the
corridor. The number of bridges off-corridor remained relatively constant between 1992 and
2009, while the number of bridges on the corridor increased by almost 2400 over that period of
time. An interesting trend is that the difference between the number of bridges grew smaller
over time.
UDUTC Final Report
Page 28
3.3.2 Age of Bridges
Figure 3.3 shows the average age of the bridges on and off the BOSFOLK corridor.
Average Age, BF Bridges
50
Average Age (years)
48
46
44
42
Age, BF Bridges off corridor
Age, BF Bridges on corridor
40
38
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 3.3 Average age of macroview bridges on- and off-corridor
The average age of both groups increased steadily over time, indicating a gradual aging of the
inventory. The average age for the on- and off-corridor bridge was almost identical, until about
1999. After 1999, the age of on-corridor bridges increased, and began to increase at a faster
rate than the off-corridor bridges.
In 2009, the average age of the on-corridor bridges was almost 47, and the average age of the
off-corridor bridges was just over 48. The average rate of aging of the on-corridor group in 2009
was approximately 0.36 years-per-year; the average rate of aging of the off-corridor group in
2009 was approximately 0.30 years-per-year. At these rates the on-corridor group would reach
an average age of 50 years old (the design life of a bridge built some decades ago) in 2014; the
off-corridor group would reach an average age of 50 in 2019. This shows that the on-corridor
group will reach its design life earlier than the off-corridor group. The differences could be due
to more new bridges being build off of the corridor, and/or more older bridges being taken out
of service or being replaced off of the corridor, than on the corridor during that time.
UDUTC Final Report
Page 29
3.3.3 Average Roadway Area
Figure 3.4 shows the average roadway area for the bridges on the macroview definition of the
BOSFOLK corridor.
Average Roadway Area, BF Bridges
1,000
Average Roadway Area (m2)
900
800
700
600
500
400
300
Roadway Area, BF Bridges off corridor
Roadway Area, BF Bridges on corridor
200
100
0
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 3.4 Average roadway areas for macroview bridges on- and off-corridor
The average roadway area of bridges on the corridor was more than double the area of offcorridor bridges during this time. This indicates a great disparity between the two groups of
bridges. The results show that on average, bridges on the corridor are longer and/or wider
than bridges off of the corridor.
3.3.4 Estimate Total Roadway Area
In addition to the average bridge roadway area, the estimated total bridge roadway area was
calculated for on- and off-the corridor, as described previously in Chapter 2. As justification for
the calculation, Table 3.4 shows the percentage of records that were missing either the
structure length (item 49) or the roadway width (item 51) from the bridge record.
Table 3.4 Blank entries in calculating roadway area of on-and off-corridor macroview bridges
Year
92
93
94
On-Corridor Macroview Bridges
Records
Blanks
% Blank
35,411
2,788
7.87
35,550
2,959
8.32
35,830
3,123
8.72
UDUTC Final Report
Off-Corridor Macroview Bridges
Records
Blanks
% Blank
40,605
3,408
8.39
40,600
3,504
8.63
40,534
3,605
8.89
Page 30
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
36,269
36,251
36,408
36,353
36,559
36,669
36,786
36,827
37,045
37,245
37,192
37,424
37,632
37,729
37,788
3,188
3,219
3,174
3,104
3,138
3,153
3,210
3,210
3,244
3,345
3,472
3,526
3,580
3,601
3,665
8.79
8.88
8.72
8.54
8.58
8.60
8.73
8.72
8.76
8.98
9.34
9.42
9.51
9.54
9.70
40,750
40,450
40,344
40,103
40,163
40,228
40,272
40,394
40,435
40,468
40,631
40,642
40,635
40,607
40,596
3,676
3,693
3,714
3,629
3,663
3,704
3,754
3,787
3,789
3,766
3,774
3,819
3,813
3,797
3,810
9.02
9.13
9.21
9.05
9.12
9.21
9.32
9.38
9.37
9.31
9.29
9.40
9.38
9.35
9.39
The average percentage of records that were missing roadway area data was 8.87% for oncorridor bridges and 9.16% for off-corridor bridges. Thus in both cases more than 90% of the
records contained complete information which resulted in a good estimate of the average road
area, and consequently we can also assume a good estimate of the total roadway area. Figure
3.4 shows the estimated total roadway area for on- and off-corridor bridges in the BOSFOLK
macroview definition.
UDUTC Final Report
Page 31
Calculated Total Roadway Area (million m2)
Estimated Total Roadway Area, BF Bridges
40
35
30
25
20
15
Calculated Total Roadway Area, BF Bridges off corridor
10
Calculated Total Roadway Area, BF Bridges on corridor
5
0
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 3.5 Estimated total roadway area values for macroview bridges on- and off-corridor
The total roadway area for bridges on the corridor was consistently greater than the total area
of the off-corridor bridges, by a factor of almost 2. The difference between the trend lines did
not change significantly over time. This result shows that while the number of bridges on the
corridor was slightly less than off the corridor, the total bridge roadway area was almost twice
what it was off the corridor.
3.3.5 Average Daily Traffic
Figure 3.6 shows the average Average Daily Traffic (ADT) versus year for bridges on- and off- the
corridor.
UDUTC Final Report
Page 32
Average ADT, BF Bridges
25,000
Average ADT
20,000
15,000
ADT, BF Bridges off corridor
ADT, BF Bridges on corridor
10,000
5,000
0
92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09
Year
Figure 3.6 Average ADT values for macroview bridges on- and off-corridor
As one would expect, the average ADT for on-corridor bridges was much higher than for offcorridor bridges. The bridges on the macroview definition of the BOSFOLK corridor saw traffic
volumes between 3 and 4 times greater than the bridges off the corridor. The average ADT
increased slightly over time for both groups, showing a slight increase in traffic volume overall
with time. Higher traffic volumes expose bridges to a greater number of loading cycles, which
can be a concern if a bridge is prone to fatigue. One can see that bridges on the macroview
corridor experienced a greater number of loading cycles than the bridges off of the corridor.
3.3.6 Average Daily Truck Traffic
Figure 3.7 shows the ADTT for the bridges on the corridor and off the corridor.
UDUTC Final Report
Page 33
Average ADTT, BF Bridges
1,800
1,600
1,400
Average ADTT
1,200
ADTT, BF Bridges off corridor
1,000
ADTT, BF Bridges on corridor
800
600
400
200
0
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 3.7 Average ADTT values for macroview bridges on- and off-corridor
The average ADTT for bridges on the corridor was consistently more than 2 times the ADTT off
the corridor. Like the ADT volumes, the ADTT indicates that the bridges on the BOSFOLK
corridor experienced more heavy loading cycles due to trucks. Higher ADTT is usually associated
with more heavy load cycles, i.e., more higher stress levels, which can cause problems in
bridges.
3.3.7 Sufficiency Rating
Sufficiency rating is a gross indicator of overall bridge performance and takes into account
things other than the condition of the structure. The average sufficiency rating was calculated
for each year’s bridge records. This calculation was performed for the bridges both on-corridor
and off-corridor. These average sufficiency ratings are shown in Figure 3.8.
UDUTC Final Report
Page 34
Sufficiency Rating, BF Bridges
Sufficiency Rating (out of 100)
90
85
80
75
70
SR, BF Bridges off corridor
SR, BF Bridges on corridor
65
60
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 3.8 Average sufficiency ratings for macroview bridges on- and off-corridor
The average sufficiency rating for both groups of bridges varied within a close range of 65 to 80
over the 18 year period. The average for bridges on-corridor was consistently higher than for
bridges off-corridor. This indicates a higher degree of resilience for bridges on or near the
major interstate backbone of the BOSFOLK corridor. The average sufficiency rating for both
groups increased over time; values began in the upper 60s (off-corridor)/low 70s (on-corridor),
and ended in the upper 70s for both by 2009. By this indicator, the performance of both groups
of bridges overall improved over time.
3.3.8 Operationally Posted Bridges
Presented in Figure 3.9 is a plot of the percentage of operationally posted bridges for on- and
off-corridor. The results are derived from item 41, which defines a bridge as open, posted, or
closed to traffic. This item assigned each bridge one of 8 type codes to indicate the bridge’s
functional status. A type code “A” (Open, no restrictions) is most desirable in terms of
performance; a type code “P” (Posted for load) indicates a structure had a posting for a level of
load less than its full capacity. The number of bridges in each group was not significantly
different; in 2009 there were 37,833 on-corridor bridges and 40,596 off-corridor bridges. This
difference in total number of bridges was not large enough to affect the number of bridges
represented by the percentages shown in the plots. Three column plots were created to
identify trends. Figure 3.9 shows the percentage of all bridges that were assigned any type
code other than “A.”
UDUTC Final Report
Page 35
% of Operationally Posted BF Bridges
Percent of Total Bridges
25
% Oper. Posted, BF Bridges off corridor
% Oper. Posted, BF Bridges on corridor
20
15
10
5
0
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 3.9 Percentage of macroview bridges with an operational posting (other than “A”)
The percentage of bridges that had type codes other than “A” decreased over time. This
decrease occurred for both the on-corridor and off-corridor bridges. The percentages for both
groups also converged slightly. Based on this parameter, the performance of both groups of
bridges can be said to have improved over time. The percentage of off-corridor bridges without
an “A” type code was consistently higher than for on-corridor bridges. By this measure there
were a greater percentage of bridges off of the corridor that were for some reason in a poorer
state, than those on the corridor. Stated another way, the on-corridor bridges showed better
performance than the bridges off of the corridor.
3.3.9 Operationally “A” Posted Bridges
The column plot in Figure 3.10 shows the percentage of all bridges assigned a type code of “A”
(note that Figure 3.10 is just the compliment of Figure 3.9).
UDUTC Final Report
Page 36
% of Operationally "A" Posted BF Bridges
Percent of Total Bridges
92
90
88
% of A Oper. Posted, BF Bridges off corridor
% of A Oper. Posted, BF Bridges on corridor
86
84
82
80
78
76
74
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 3.10 Percentage of macroview bridges posted “A” (Open, no restriction)
The results presented in Figure 3.10 show that over time there was a gradual increase in the
number of bridges classified as type “A”, which indicates an overall improvement in the
condition of the inventory. The percentage of operationally “A” posted bridges on the corridor
was always greater than those off the corridor. These results again illustrate that in general the
bridges on the corridor were in better condition than those off of the corridor, and that as a
percentage more bridges on the corridor were “open” than were bridges off of the corridor.
3.3.10 Operationally “P” Posted Bridges
Figure 3.11 presents the “% of Operationally “P” Posted,” which shows the percentage of all
bridges that had a load posting (worst of the eight designations). This distinguished the
percentage of bridges posted” P” from the percentage bridges with a type code other than “A.”
Bridges posted for load were of special interest, because this indicates a diminished capacity to
carry load.
UDUTC Final Report
Page 37
Percent of Total Bridges
% of Operationally "P" Posted BF Bridges
18
16
14
12
10
8
6
4
2
0
% of P Oper. Posted, BF Bridges off corridor
% of P Oper. Posted, BF Bridges on corridor
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 3.11 Percentage of macroview bridges posted “P” (Posted for load)
Comparing Figure 3.11 with Figure 3.9 one can see that the percentage of bridges posted for
load comprised nearly the total percentage of bridges that had some designation other than
“A” (Open, no restriction), i.e., most bridges were either type “A” or type “P”. Both groups of
bridges showed a decrease in the percentage of bridges posted for load, which by this measure
suggests an overall improvement in the condition of the inventory. The difference between the
percentages also decreased over time, with both being less than 10% by 2005.
The percentage of bridges posted for load on the corridor was consistently lower than that of
the bridges off of the corridor. This finding is not surprising since a load posting on a major
interstate like I-95 or one of its major tributaries would be very undesirable. This result
indicates that the on-corridor bridge performance was consistently better than it was for the
bridges off-corridor.
3.3.11 Bridges Posted for Load
The percentage of posted bridges was derived from Item 70 – Bridge Posting. This item is
similar to Item 41 because it identifies bridges that had been posted for load. The difference
between the two is that item 41 only indicates that a bridge has been posted, whereas item 70
classifies the load level of the posting. This quantitative appraisal of a bridge’s posting indicates
how much load a bridge could legally carry. One of 6 type codes is assigned to each bridge in
the database; the code type describes the relationship between a bridge’s posting and its
maximum allowable load level. The type code “5” (Equal to or above legal loads) means a
structure does not require posting to be in service. Values ranging from “4” (0.1-9.9% below) to
“0” (>39.9% below) indicates the load level for which a structure has been posted.
UDUTC Final Report
Page 38
One can assume that the condition of a bridge is very closely tied to its posting, i.e., if a bridge is
posted there is a very good chance that it has experienced some deterioration or damage that
is restricting its load carrying capacity. Thus, this measure is very indicative of the condition of a
bridge, and besides the structure condition ratings, is perhaps the most direct indicator of
performance.
Presented in Figure 3.12 is a column plot of the sum total number of bridges with a type code
“0”, “1”, “2”, “3”, or “4” for item 70, presented as a percentage of the total number of bridges.
Percent of Total Bridges
% Posted, BF Bridges
20
18
16
14
12
10
8
6
4
2
0
% Posted, BF Bridges off corridor
% Posted, BF Bridges on corridor
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 3.12 Percentage of load postings (item 70) for macroview bridges on- and off-corridor
The trend is very similar to that seen in Figure 3.11: there was a gradual decrease in the fraction
of posted bridges with time, and a greater percentage of bridges off the corridor were posted
than on the corridor. This indicates that as a percentage, more bridges on the corridor could be
loaded to their maximum operating load levels than bridges off the corridor. Both groups of
bridges showed a decrease in the percentage of bridges posted, which again, by this measure
suggests an overall improvement in the condition of the inventory. The performance of both
groups improved at about the same rate.
Comparing Figure 3.11 and Figure 3.12 one might expect the plots to be identical, since Figure
3.11 indicates the fraction of bridges that were operationally posted “P”, and Figure 3.12
indicates the load level of bridges that have been posted due to limited load carrying capacity.
Differences can be noted, particularly on the non-corridor results between 1992 and 1998. The
coding items, however, are not identical and there can be differences in the way the items are
recorded in the NBI. The differences are alluded to in the Coding Guide (Recording, 1995).
UDUTC Final Report
Page 39
3.3.12 Condition Ratings
As discussed in Chapter 2, condition ratings are numeric values between 0 and 9 that are
assigned to the bridge deck, superstructure, and substructure that provide an overall
assessment of the condition of these major components of a bridge. A condition rating of 0 is a
failed condition, out of service, a condition rating of 9 is excellent condition. A condition rating
of 5 is fair condition, implying that all primary structural components are sound but may have
minor section loss, cracking, deterioration, spalling or scour. A condition rating of 6 is
satisfactory condition, implying structural elements show some minor deterioration. A
condition rating of 7 is good condition, implying some minor problems.
The average condition ratings for the on-corridor and off-corridor groups were calculated for
the 18 years; these results are shown in Figure 3.13, Figure 3.14 and Figure 3.15.
Average Deck Condition Ratings, BF Bridges
Average Deck Rating
7
6.5
6
Cond. Rating, BF Bridges off
corridor
Cond. Rating, BF Bridges on
corridor
5.5
5
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 3.13 Average deck condition ratings for macroview bridges on- and off-corridor
UDUTC Final Report
Page 40
Average Superstructure Condition
Ratings, BF Bridges
Average Superstructure Rating
7
6.5
6
Cond. Rating, BF Bridges off
corridor
Cond. Rating, BF Bridges on
corridor
5.5
5
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 3.14 Average superstructure condition ratings for macroview bridges on- and offcorridor
Average Substructure Condition
Ratings, BF Bridges
Average Substructure Rating
7
6.5
6
Cond. Rating, BF Bridges off
corridor
Cond. Rating, BF Bridges on
corridor
5.5
5
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 3.15 Average substructure condition ratings for macroview bridges on- and off-corridor
UDUTC Final Report
Page 41
The average condition ratings for all three major components were higher for the on-corridor
group than for the off-corridor group, over the entire 18 years. This suggests better overall
performance of the on-corridor group versus the off-corridor group. The ratings were fairly
stable for the on-corridor group and varied between 6 and 6.5, implying an average condition of
somewhere between satisfactory and good for that group. The average condition ratings were
less than satisfactory for the off-corridor group until 1999 when they increased slightly to just
above 6. Since 1999 the average condition rating of all three major components was
satisfactory for the off-corridor group.
3.3.13 Normalized Operating Rating
A bridge’s operating rating defines the maximum allowable load level that the bridge may be
subjected to. Every NBI bridge record has a value for operating rating. The values were
normalized by the MS18 design truck load, which weighs 32.4 metric tons. In this way,
normalized values greater than 1.0 indicate a rating greater than 32.4 metric tons. It is ideal for
bridges to have operating ratings above the MS18 design load; values above 1.0 were
considered to indicate resilience. Figure 3.16 shows the average normalized operating ratings
for bridges on and off the macroview BOSFOLK corridor.
Normalized Operating Ratings, BF Bridges
Rating, normalized for MS18 (32.4 metric tons)
2
1.9
1.8
1.7
1.6
1.5
Op. Rat., BF Bridges off corridor
Op. Rat., BF Bridges on corridor
1.4
1.3
1.2
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 3.16 Average normalized operating ratings for macroview bridges on- and off-corridor
UDUTC Final Report
Page 42
For both groups the average operating rating increased over the 18 years, from between 1.4
and 1.5 to just over 1.8 in 2009. The off-corridor bridges historically had a slightly higher
average operating rating than the bridges on-corridor. The on-corridor bridges did not meet or
exceed the off-corridor average rating until 2004. A larger average operating rating means that
the bridges could withstand a higher maximum load level. This trend indicates an overall
improvement in performance of the inventory over time.
3.3.14 Normalized Inventory Rating
A bridge’s inventory rating is a measure of bridge load capacity. The inventory rating defines
the load level to which a bridge may be safely subjected for an indefinite period of time. The
NBI values for inventory rating are also reported in metric tons. These values were normalized
by the MS18 design truck load value of 32.4 metric tons. Values greater than 1.0 are a positive
indicator of performance. Bridges with higher acceptable long-term load levels were deemed
more resilient than bridges rated for lower inventory load levels. Figure 3.17 shows the
average normalized inventory ratings for bridges on and off the macroview BOSFOLK corridor.
Normalized Inventory Ratings, BF Bridges
Rating, normalized for MS18 (32.4 metric tons)
1.3
1.2
1.1
1
Inv. Rat., BF Bridges off corridor
Inv. Rat., BF Bridges on corridor
0.9
0.8
0.7
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 3.17 Average normalized inventory ratings for macroview bridges on- and off-corridor
Much like the operating rating results, the average inventory rating increased over time, which
suggests an overall gradual improvement in the condition of the inventories in recent years.
The average ratings were both below 1 in 1992 indicating that on average the inventory
UDUTC Final Report
Page 43
capacity was below the legal limit. The on-corridor ratings were initially lower than the offcorridor ratings, but exceed the off-corridor rating from 1996 on. After that the on-corridor
average rating is higher than the off-corridor.
3.3.15 Average Posted Roadway Area
Presented in Figure 3.18 is the average roadway area for posted bridges on- and off the
corridor. This plot includes data for any bridge for which Item 70 – Bridge Posting, is anything
other than a 5.
Average Posted Roadway Area, BF Bridges
Average Posted Roadway Area (m2)
450
400
350
300
250
200
150
100
Posted Roadway Area, BF Bridges off corridor
Posted Roadway Area, BF Bridges on corridor
50
0
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 3.18 Average posted roadway area for macroview bridges on- and off-corridor
The average posted roadway area was greater for the on-corridor bridges than it was for
bridges off-corridor, over the entire 18 year period. The average posted area off-corridor was
just under 150 m2, while on-corridor it varied between 300 and 400 m2. The sudden change in
the on-corridor average does not seem to correlate with any changes off-corridor for
corresponding years. Referring to Figure 3.4, which shows that the average roadway area of
the on-corridor bridges is greater than that of the off-corridor bridges, it is not surprising that
the average posted roadway for on-corridor is also greater than that of the off-corridor bridges.
3.3.16 Estimated Total Posted Roadway Area
Similar to the method used to estimate the total roadway area, the total posted roadway area
was estimated. Table 3.5 shows the number of records for posted bridges for each year, and
the percentage of records that were deemed “blank” due to missing information.
UDUTC Final Report
Page 44
Table 3.5 Blank entries in calculating roadway area of on- and off-corridor macroview posted
bridges
Year
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
On-Corridor
Records
Blanks
% Blank
4,131
55
1.33
3,946
64
1.62
3,242
59
1.82
3,190
55
1.72
3,123
74
2.37
2,960
82
2.77
3,942
80
2.03
3,110
57
1.83
2,919
45
1.54
2,813
48
1.71
2,676
51
1.91
2,619
58
2.21
2,591
44
1.70
2,416
43
1.78
2,351
54
2.30
2,326
59
2.54
2,260
52
2.30
2,214
50
2.26
Off-Corridor
Records
Blanks
% Blank
7,074
45
0.64
6,779
49
0.72
6,531
49
0.75
6,353
52
0.82
6,139
49
0.80
5,945
51
0.86
5,718
51
0.89
5,466
52
0.95
5,226
51
0.98
5,071
65
1.28
4,874
61
1.25
4,687
60
1.28
4,473
41
0.92
4,329
34
0.79
4,179
43
1.03
4,153
46
1.11
4,069
42
1.03
3,924
36
0.92
The fraction of records for posted bridges with missing data was very small, and well below the
fraction shown earlier for the entire bridge population. Less than 2.8% were missing data for
on-corridor and less than 1.3% for off-corridor. Thus the calculation of the estimated total
posted roadway area should be very accurate. Figure 3.19 shows the estimated total posted
roadway area for macroview bridges on and off the BOSFOLK corridor.
UDUTC Final Report
Page 45
Estimated Total Posted Roadway Area (million m2)
Estimated Total Posted Roadway Area, BF Bridges
1.8
1.6
1.4
1.2
1
0.8
0.6
Calculated Total Posted Roadway Area, BF Bridges off corridor
0.4
Calculated Total Posted Roadway Area, BF Bridges on corridor
0.2
0
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 3.19 Estimated total posted roadway area for macroview bridges on- and off-corridor
The total posted roadway area for both groups decreased over time, which again suggests a
general improvement of condition of the inventory over time. The large “spike” of the oncorridor trend line in 1998 was attributed to an atypically large number of records for posted
bridges (there were 2,960 records of posted bridges in 1997; this number increased to 3,942 in
1998). The trend lines converged over time, which meant the total roadway area of on-corridor
posted bridges had diminished. This change indicated better performance for the bridges on
the BOSOFLK corridor. The on-corridor bridges were said to have improved as a result of
smaller total posted roadway area. Thus, while the average posted roadway area for the oncorridor bridges is almost twice that of the off-corridor bridges, the total posted is only slightly
higher for the on-corridor group.
3.4 Summary of Findings for Macroview Corridor
The macroview BOSFOLK database compared the aggregate performance of two groups of
bridges. The groups were defined as being on-corridor or off-corridor. The bridges defined as
on-corridor were in a wide area surrounding the main interstate arterial routes of the BOSFOLK
corridor; the off-corridor bridges were those remaining bridges in the selected counties of the
states carrying the corridor. Approximately 44% of the counties and just over 48% of the
bridges in the macroview database were on-corridor, yielding a very well balanced database of
on-corridor and off-corridor bridges. Table 3.6 shows a concise summary of the parameter
UDUTC Final Report
Page 46
comparisons made between the on- and off-corridor inventories. The key findings and
conclusions from the analysis of the macroview database are as follows:
1. The number of bridges in the on-corridor inventory was slightly less than the number in
the off-corridor inventory. The number in the on-corridor inventory increased slightly
over time; however, the number in the off-corridor inventory remained about the same.
2. The average age of bridges on- and off- of the corridor increased with time, with the
average age of the bridges on-corridor being slightly greater than those off-corridor in
2009. The on-corridor group aged at a slightly faster rate than the off-corridor group.
The difference in average age means that a larger fraction of new bridges were being
introduced to the off-corridor inventory, or more older bridges were being removed and
not being replaced than for the on-corridor inventory.
3. The average roadway area of bridges on the corridor was more than twice that of the
bridges off of the corridor. The estimated total roadway area of bridges on the corridor
was approximately 2 times the total area of bridges off of the corridor. The average
areas increased only slightly over the 18 year period; the total area of both groups
increased gradually over the 18 year period.
4. As would be expected, the general traffic and truck traffic on bridges on the corridor
was greater than the traffic on the bridges off of the corridor. The on-corridor ADT was
more than 3 times the off-corridor ADT, and the on-corridor ADTT was more than 2
times the off-corridor ADTT. Higher traffic volumes imply a larger number of load cycles
and a larger number of high load cycles for the on-corridor bridges, as compared to the
off-corridor bridges. Thus there is clearly higher demand on the on-corridor bridges than
there is on the off-corridor bridges.
5. The average sufficiency rating for on-corridor bridges was greater than that for the offcorridor bridges over the 18 year period. The average sufficiency rating increased
slightly over time, indicating a gradual overall improvement in the condition of both
inventories. The on-corridor average was always larger than the off-corridor average,
indicating slightly better performance of the on-corridor bridges.
6. Both inventories showed a gradual decrease in the number of operationally posted
bridges over the 18 year period, indicating a gradual improvement in condition of both
inventories. A slightly larger fraction of bridges off-corridor was posted, as compared to
the bridges on-corridor. The majority of the postings were due to limited load carrying
capacity.
7. The average condition ratings of the on-corridor group were consistently higher (better)
than the off-corridor group. This suggests better overall condition of the on-corridor
group versus than the off-corridor group. The average condition ratings of the oncorridor group remained fairly stable over the 18 year period, with the average
condition falling somewhere between satisfactory and good. The average condition
UDUTC Final Report
Page 47
rating of the off-corridor group was less than satisfactory before 1999. After 1999 the
average rating increased into the satisfactory range.
8. The average operating and inventory ratings for both inventories increased over time,
indicating a gradual improvement in condition of both inventories. The average
operating rating of the off-corridor group was slightly higher than the on-corridor group,
at least up until 2004, when they converged. The average inventory rating of the oncorridor group was slightly higher than the off-corridor group for most of the 18 years.
9. The percentage of posted bridges on and off of the corridor decreased from 1992 to
2009, indicating an overall improvement of condition of the inventories over time. The
fraction of bridges on-corridor posted was consistently lower than the fraction off of the
corridor.
10. The average posted roadway area of the on-corridor bridges was approximately twice
that of the off-corridor bridges, for the entire 18 years. However, the total posted
roadway area was just slightly higher for the on-corridor inventory. The total posted
roadway area decreased over time for both groups, indicating a gradual improvement of
condition of the both inventories.
Table 3.6 Summary comparison of macroview results
Parameter
Number of bridges
Age
Average roadway area
Total roadway area
ADT
ADTT
SR
# posted
Condition ratings
Operating rating
Inventory rating
Average posted roadway area
Total posted roadway area
On-corridor
On <
On ~=
On (2x) >
On (2x) >
On (3-4x) >
On (2x) >
On >
On <
On >
On ~=
On ~=
On (2x) >
On ~=>
Off-corridor
Off
Off
Off
Off
Off
Off
Off
Off
Off
Off
Off
Off
Off
In summary, the macroview analysis revealed that the on-corridor inventory of bridges, while
only slightly fewer in number and older than the off-corridor inventory, accounted for more
bridge roadway area and was exposed to higher traffic volumes than the off-corridor inventory.
However, by most of the tangible performance measures, which includes sufficiency rating,
postings, and condition ratings, the on-corridor inventory performed better than the offcorridor inventory: the operating and inventory ratings were similar for both inventories. In
UDUTC Final Report
Page 48
addition, the total posted roadway area for the on-corridor inventory was only slightly higher
than that of the off-corridor inventory. Thus, while there was more demand on the on-corridor
inventory, the inventory performed better overall, than the off-corridor inventory. It should be
noted that every performance measure, for both inventories, either improved or remained
about the same during the 18 year period, indicating general overall improvement of the entire
inventory over time
UDUTC Final Report
Page 49
UDUTC Final Report
Page 50
4 Microview Results
The Microview BOSFOLK-NBI database was the second of the two methods used to study the
resilience of bridges on the corridor. This chapter outlines the approach used to define the
microview version of the corridor, the steps to create the microview database, and the results
of analyzing the performance parameters. The microview database used a much more
narrowly defined view of the physical extent of the corridor, that is more closely tied to
Interstate 95 and the major arterial roads that connect to it. Note that the macroview oncorridor database was the basis, i.e., starting point, for the microview databases.
4.1 The Microview BOSFOLK-NBI Corridor
4.1.1 Defining the Microview Corridor
The path of I-95 determined which states were selected as part of the BOSFOLK corridor. The
microview database was based on the same 11 states and the District of Columbia, used in the
macroview. Table 4.1 shows the number of bridges (combined, on- and off-corridor) that were
part of the microview database and the total number of bridges in each state. The percentages
of microview bridges compared to the total number in each state for 2009 is also shown.
Table 4.1 Number of bridges in microview BOSFOLK-NBI database in 2009
State
New Hampshire
Massachusetts
Rhode Island
Connecticut
New York
New Jersey
Pennsylvania
Delaware
Maryland
District of Columbia
Virginia
Total
Bridges in Microview Total Bridges in State % of State Total
676
2,509
26.9
5,043
5,043
100
768
768
100
4,187
4,187
100
4,027
17,375
23.2
6,486
6,486
100
5,569
22,313
25.0
862
862
100
4,485
5,205
86.2
246
246
100
5,292
13,537
39.1
37,641
78,531
47.9
The microview contained fewer bridges mostly because the states of greater size did not
contribute all of their bridges to the off-corridor portion of the database. The same six states
that included all of their bridges in the macroview database again contributed all of their
bridges to the microview. This was done to simplify the creation of the microview database by
selecting bridges by counties, instead of selecting them individually.
UDUTC Final Report
Page 51
4.1.2 Classification of Bridges: On-corridor and Off-corridor
As was done for the macroview database, the microview bridge records were split into two
categories. The first contained records for bridges that were on I-95 and the major arteries that
connect to it or are in close proximity to it; these were defined as “on-corridor” bridges. The
second category defined bridges located outside the influence zone of I-95; these were defined
as the “off-corridor” bridges. These two paired databases were titled “Microview On-Corridor”
and “Microview Off-Corridor.”
4.1.3 Selection of Counties and Bridges in the Microview
A method was developed to delineate the region defined by the microview definition of the
BOSFOLK corridor. The basis of the microview definition was formed by selecting the counties
to be used in creating this more exclusive view of the BOSFOLK corridor. The same counties
selected for the “Macroview On-Corridor” database now formed the pool from which the
microview database would be created. This formed the outermost boundary of the microview
database; the extent of this database was restricted to a much smaller area than what was used
to define the larger macroview database. Maps were obtained that show both the major
highway routes and the boundaries of counties in selected BOSFOLK states. The path of I-95
was identified between Boston and Norfolk. The selection of I-95 formed the basis for the oncorridor sub-database. It was decided that selecting bridges carrying only I-95 would discount
the influence of other interstate routes along the corridor. The influence of interstate highways
was important to determining on-corridor performance, and their inclusion provided a more
accurate representation of the roadway network affected by the BOSFOLK corridor. So it was
decided that other interstate routes should be included as part of the microview on-corridor
definition. Additional interstate bridges were selected based on their route and proximity to I95, the backbone of the BOSFOLK corridor. Interstates that coincided with the path of I-95
were included. Also included were highways that parallel but do not cross I-95, or those
highways that “feed” coinciding highways but do not cross I-95. The length of these selected
interstate routes affected the number of bridges each route contributed to the on-corridor
microview database. The inclusion of a long stretch of interstate meant more bridges were
considered on-corridor. No bridges beyond the edges of the microview-defined area were
selected as part of the on-corridor group of bridges. This method produced a web of interstate
routes that was centric to I-95. These highways’ bridge records established the microview oncorridor database. The off-corridor database was comprised of all remaining records in the
counties selected to map the microview. Table 4.2 shows the number of state counties
selected for use in the microview, as well as the percentages of total counties represented in
the microview.
UDUTC Final Report
Page 52
Table 4.2 Number of counties for microview BOSFOLK database in 2009
State
New Hampshire
Massachusetts
Rhode Island
Connecticut
New York
New Jersey
Pennsylvania
Delaware
Maryland
District of Columbia
Virginia
Total
Microview Counties Total State Counties % of Total State Counties
3
10
30
14
14
100
5
5
100
8
8
100
12
62
19.35
21
21
100
10
67
14.92
3
3
100
21
24
87.5
1
1
100
56
133
42.10
154
348
44.25
The microview database includes about 44% of all BOSFOLK state counties; recall from Section
3.1.3 that, compared to the total number of BOSFOLK states’ counties, the percentages of
macroview counties on-corridor match the percentages of counties that make up the entire
microview database. This highlighted the fact that extent of the microview definition was
created from only the on-corridor section of the macroview database. Both the on-corridor
macroview and the entire microview database comprised about 44% of all BOSFOLK states’
counties. The 100% inclusion of a state’s counties to the microview corridor did not dictate
that 100% of that state’s interstate bridges would be included in the on-corridor database. The
number of interstate bridges included in each state’s on-corridor database depended on those
interstate routes’ length, geographic orientation, and coincidence with I-95.
Presented in Figure 4.1 is a map of the region and highways included in the microview
database. The counties included are shown in blue on the map. The highways included in the
on-corridor database are shown in red on the map. Regions shown in gray were not part of the
microview database.
UDUTC Final Report
Page 53
Figure 4.1 Map of selected counties in the BOSFOLK microview
Table 4.3 shows the number of bridges defined as on- and off-corridor for the microview
database in 2009. This excluded any bridges that were less than 20 feet (6.1 meters) in length.
The low percentage of bridges on-corridor versus off-corridor is an indication of the “narrow”
definition of the BOSFOLK-NBI Microview database.
UDUTC Final Report
Page 54
Table 4.3 Number of bridges on- and off-corridor for BOSFOLK microview database in 2009
State
New Hampshire
Massachusetts
Rhode Island
Connecticut
New York
New Jersey
Pennsylvania
Delaware
Maryland
District of Columbia
Virginia
Total
On-Corridor Off-Corridor % On-Corridor
95
581
14.1
396
4,647
7.9
132
636
17.2
359
3,828
8.6
334
3,693
8.3
880
5,606
13.6
410
5,159
7.4
89
773
10.3
587
3,898
13.1
65
181
26.4
985
4,307
18.6
4,332
33,309
11.5
The number of on-corridor bridges represented just 11.5% of the total number of bridges in the
microview database. This was indicative of the small number of interstate bridges compared to
the much greater number of off-corridor bridges in the microview database. The on-corridor
database was relatively small, even with the extension of the on-corridor definition to include
the larger network of interstate highways. The percentage of bridges on-corridor was not
widely varied in the individual states. The area with the highest percent of bridges on-corridor
was the District of Columbia; just over 26% of its bridges being interstates in connection with I95. This high percentage was attributed to the relatively small size of this region, and the fact
that several major interstate highways exist not far from Washington, D.C. This was the only
state/district with more than 20% of its bridges in the on-corridor database.
4.2 Creation of the Microview Database
The process for creating the microview on-corridor and microview off-corridor databases was
as described in Chapter 2. Specific details are outlined below.
4.2.1 Creation of Microview-Specific State Databases
Certain data needed to be excluded to create the microview databases. The bridge “under”
records were excluded. Also, records for bridges less than 20 ft in length were deleted.
Two important sets of criteria were used to filter the growing microview databases; the first
was the identification of states’ counties, which were then used to collect selected geographic
groups of bridges as was done for the creation of the macroview database; the second sorting
criteria were the route identifier and route number, which were used to isolate the interstate
bridges in the microview corridor. The microview definition of the BOSFOLK corridor
necessitated that all states have their records split into two databases: one for the interstate
UDUTC Final Report
Page 55
bridges on-corridor and one for those that were off-corridor. The bridges needed to be
organized according to the on-corridor and off-corridor organization schemes detailed in Table
4.3 and Figure 4.1. This was done using the Federal Information Processing Standards (FIPS)
codes, which assigned a 3-digit code to every county or specially designated area in a state.
Some urban areas in Virginia and Maryland were designated independent cities, but most
BOSFOLK states used counties to apportion their lands. The FIPS codes could select entire
counties of bridges, in any desired combination. The names of these counties were identified
and paired to their corresponding FIPS codes. In this way, the limits of the off-corridor
microview database were defined by selecting the desired counties. The records in each
BOSFOLK states’ Access databases were split according to these county codes and route
identifiers. The records that resulted from these sorting procedures were defined as on- and
off-corridor.
4.2.2 Transferring Access Tables to Excel Files
The microview databases of records were transferred to Excel files. On-corridor and offcorridor records were kept in separate Excel files, in keeping with the organization scheme of
the Access databases. The files of compiled records of the microview database were identical
to the files created to individually analyze bridges’ behavior. Each file contained 18
spreadsheets, one for each year’s worth of bridge records. Performance data was analyzed
using columns of calculations, located at the trailing edge of each year’s data. Results of the
yearly statistical analyses were compiled in a spreadsheet of results, which was used to
generate plots of the performance data. The files were organized by state and which microview
corridor group (on- or off-corridor) they represented; the spreadsheets in each file were
organized by which year of the microview database they accounted. These on- and off-corridor
files for each state were then compiled to create two files that contained a complete list of
macroview bridges records; one file contained the bridge records and performance analyses for
bridges on BOSFOLK corridor, while the other contained the off-corridor records. This was
done by copying the bridge records in the on- and off-corridor state files and pasting them into
their corresponding microview files. Note that the two-letter code of “BF” was used to signify
the BOSFOLK database bridges. This was done to maintain consistency with the FHWA’s use of
two-letter state codes (e.g.: DE for Delaware, PA for Pennsylvania, etc.).
4.2.3 Organization of Microview Excel Files
Recall from Section 3.2.4 that the macroview database and performance analyses contained
too many bridge records to be stored in one complete Excel file. Instead, the BOSFOLK-NBI
Macroview files were split into 3 separate files, each one of which accounted for 6 years’ data
out of the total 18 years. These files were limited strictly by the number of records contained in
each set of spreadsheets. A similar situation arose when compiling the microview off-corridor
database. This group of bridges was too numerous to store in one Excel file. The solution was
UDUTC Final Report
Page 56
to apportion the data into 3 separate files, just as was done for the macroview file. The 3 files
that held the off-corridor records and results of yearly analyses were created by dividing the
database into 6-year periods for 1992-1997, 1998-2003, and 2004-2009. The decision was
made to split these records and statistical analyses into the smaller files. This necessary
reorganization of the BOSFOLK microview records did not affect the analyses performed to
determine performance trends for the bridges. Instead of one file containing all data for the 18
years, the macroview analysis was organized into 4 separate files: 3 contained the records and
statistical analyses, and 1 contained the aggregate statistical analysis and plots of historic data.
The series of plots in Section 4.3 was the result of these statistical analyses. The plots
compared performance parameter data for microview on-corridor and off-corridor bridges.
4.3 Results of Performance Analysis
Presented in this section are the results of the analyses of the data from the microview
databases.
4.3.1 Number of Bridges
Figure 4.2 shows the total number of bridges in the on-corridor and off-corridor microview
databases between 1992 and 2009.
Number of Bridges, BF Bridges
35,000
Number of Bridges
30,000
25,000
No. of BF Bridges not on corridor
20,000
No. of BF Bridges on corridor
15,000
10,000
5,000
0
92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09
Year
Figure 4.2 Total numbers of microview bridges on- and off-corridor
UDUTC Final Report
Page 57
The number of bridges in the off-corridor inventory was more than 6 times the number of
bridges in the on-corridor inventory. The number of bridges off-corridor increased slightly over
the 18 years, while the number on-corridor remained nearly constant.
Compared to the macroview results (Figure 3.2), there is a marked difference in the number of
on-corridor and off-corridor bridges in the microview database.
4.3.2 Age of Bridges
Figure 4.3 shows the average age of the on- and off-corridor bridges in the microview database.
Average Age, BF Bridges
50
Average Age (years)
45
40
35
Age, BF Bridges not on corridor
30
25
Age, BF Bridges on corridor
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 4.3 Average ages of microview bridges on- and off-corridor
Compared to the macroview results (Figure 3.3), which recall were very similar, there are
distinct differences in the aging pattern of the on-corridor and off-corridor groups. The average
age of the off-corridor inventory was consistently higher than the on-corridor inventory;
however, the difference decreased over the years. In 2009, the average age of the on-corridor
bridges was almost 40, and the average age of the off-corridor bridges was just over 49. The
average rate of aging of the on-corridor group in 2009 was approximately 0.75 years-per-year;
the average rate of aging of the off-corridor group in 2009 was approximately 0.39 years-peryear. At these rates the on-corridor group would reach an average age of 50 years old (the
design life of a bridge built some decades ago) in 2035; the off-corridor group would have
reached an average age of 50 in 2011.
UDUTC Final Report
Page 58
4.3.3 Average Roadway Area
Figure 4.4 shows the average roadway area for the bridges on the microview definition of the
corridor.
Average Roadway Area, BF Bridges
Average Roadway Area (m2)
3,000
2,500
2,000
Roadway Area, BF Bridges not on corridor
Roadway Area, BF Bridges on corridor
1,500
1,000
500
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 4.4 Average roadway areas of microview bridges on- and off-corridor
The average roadway area of the on-corridor bridges is almost 4 times the area of the offcorridor bridges, this compared to twice in the macroview (Figure 3.4). The difference is nearly
constant over the study period. Here again, this demonstrates that on average bridges on the
corridor are longer and/or wider than bridges off of the corridor.
4.3.4 Estimated Total Roadway Area
The total roadway area was estimated using the same approach described previously for the
macroview database: the average roadway area times the number of bridges. This was again
necessary because some NBI records were missing data for structure length or roadway width,
which precluded calculating the total roadway area by summing the individual roadway areas.
Table 4.4 shows the number of records in the on-corridor and off-corridor databases with one
or more blank entries for structure length or roadway width.
Table 4.4 Blank entries in calculating roadway area of on-and off-corridor microview bridges
Year
92
On-Corridor Microview Bridges
Records
Blanks
% Blank
3,862
370
9.58
UDUTC Final Report
Off-Corridor Microview Bridges
Records
Blanks
% Blank
31,378
2,395
7.63
Page 59
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
On-Corridor Microview Bridges
4,018
364
9.06
4,111
383
9.32
4,129
391
9.47
4,198
399
9.50
4,272
417
9.76
4,295
393
9.15
4,296
396
9.22
4,317
400
9.27
4,324
401
9.27
4,310
399
9.26
4,331
399
9.21
4,302
400
9.30
4,288
402
9.38
4,309
403
9.35
4,320
400
9.26
4,333
398
9.19
4,332
396
9.14
Off-Corridor Microview Bridges
31,354
2,570
8.20
31,548
2,712
8.60
31,962
2,766
8.65
31,877
2,790
8.75
32,296
2,884
8.93
32,220
2,837
8.81
32,418
2,867
8.84
32,509
2,879
8.86
32,600
2,922
8.96
32,672
2,937
8.99
32,878
2,972
9.04
33,112
3,077
9.29
33,077
3,203
9.68
33,306
3,259
9.79
33,505
3,313
9.89
33,573
3,334
9.93
33,638
3,403
10.12
Similar to the results for the macroview database, the fraction of records with missing data
varied between 7.6% and 10.1% for the microview database. Here again, more than 90% of the
records contained complete information which resulted in a good estimate of the average road
area, and therefore a good estimate of the total roadway area. Figure 4.5 shows the estimated
total roadway area for on- and off-corridor bridges in the microview definition.
UDUTC Final Report
Page 60
Calculated Total Roadway Area (million m2)
Estimated Total Roadway Area, BF Bridges
24
22
20
18
Calculated Total Roadway Area, BF Bridges off corridor
16
Calculated Total Roadway Area, BF Bridges on corridor
14
12
10
8
6
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 4.5 Calculated total roadway area values of microview bridges on- and off-corridor
The total roadway area of the off-corridor bridges was always greater than the total area of the
on-corridor bridges. This is opposite of what was observed for the macroview database (Figure
3.5). The off-corridor total area was approximately twice the on-corridor area over the 18 year
period, despite the fact that the average roadway area of the on-corridor bridge was 4 times
that of the off-corridor bridge. The difference of course is due to the large difference in the
number of bridges. The total roadway area of both groups increased slightly over the 18 year
period, more so for the off-corridor group than for the on-corridor group.
4.3.5 Average Daily Traffic
Figure 4.6 shows the average Average Daily Traffic (ADT) versus year for bridges on- and off- the
corridor.
UDUTC Final Report
Page 61
Average ADT, BF Bridges
70,000
60,000
Average ADT
50,000
ADT, BF Bridges off corridor
40,000
ADT, BF Bridges on corridor
30,000
20,000
10,000
0
92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09
Year
Figure 4.6 Average ADT values of microview bridges on- and off-corridor
Once again, as would be expected, the traffic on the corridor was significantly higher than it
was off of the corridor. The ADT on-corridor was consistently more than 4 times greater than it
was off-corridor. This difference is about the same as that observed for the macroview
database (Figure 3.6). The average ADT increased slightly over time for the on-corridor group
but remained nearly constant off-corridor. As mentioned previously, higher traffic volumes
expose bridges to a greater number of loading cycles, which can be a concern if a bridge is
prone to fatigue. One can see that bridges on the microview corridor experienced a greater
number of loading cycles than the bridges off of the corridor.
UDUTC Final Report
Page 62
4.3.6 Average Daily Truck Traffic
Figure 4.7 shows average ADTT for both groups of bridges.
Average ADTT, BF Bridges
7,000
6,000
Average ADTT
5,000
4,000
ADTT, BF Bridges off corridor
3,000
ADTT, BF Bridges on corridor
2,000
1,000
0
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 4.7 Average ADTT values of microview bridges on- and off-corridor
The average ADTT for bridges on the corridor was consistently more than 4 times the offcorridor ADTT, and in many years was more than 5 times the off-corridor ADTT. This is
significantly greater than what was observed in the macroview results (Figure 3.7). Another
important difference is that the on-corridor ADTT increased over the years, while the offcorridor ADTT decreased slightly: average truck traffic on interstate bridges increased over 8%
between 1992 and 2009, and the off-corridor ADTT values decreased almost 17% during this
time. This indicated a greater burden was placed on the on-corridor microview bridges at the
same time the off-corridor truck loads were alleviated somewhat. Like the ADT volumes, the
ADTT indicates that the bridges on the corridor experienced more heavy loading cycles due to
trucks, which usually are associated with higher stress levels, than the bridges off the corridor.
4.3.7 Sufficiency Rating
The average sufficiency ratings are shown in Figure 4.8.
UDUTC Final Report
Page 63
Sufficiency Rating, BF Bridges
Sufficiency Rating (out of 100)
90
85
80
75
SR, BF Bridges off corridor
SR, BF Bridges on corridor
70
65
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 4.8 Average sufficiency ratings of microview bridges on- and off-corridor
The average on-corridor sufficiency rating was higher than the off-corridor rating over the
entire 18 years. This suggests that the overall condition of the on-corridor inventory is better
than that of the off-corridor inventory. Also, the sufficiency rating increased slightly for both
groups over the years, indicating an overall improvement in condition of both inventories over
the 18 year period. The trends and values shown here are slightly higher/better than those
observed for the macroview database: by this definition the sufficiency rating of the on-corridor
inventory was greater than 80% for most of the years – it never exceeded 80% in the
macroview definition.
UDUTC Final Report
Page 64
4.3.8 Operationally Posted Bridges
Presented in Figure 4.9 is a plot of the percentage of operationally posted bridges for the oncorridor and off-corridor inventories.
% of Operationally Posted BF Bridges
Percent of Total Bridges
18
16
% Oper. Posted, BF Bridges off corridor
% Oper. Posted, BF Bridges on corridor
14
12
10
8
6
4
2
0
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 4.9 Percentages of microview bridges with an operational posting
The fraction of bridges with some type of operational posting was significantly higher for the
off-corridor inventory than for the on-corridor inventory. The fraction ranged from a high of
16% to a low of just under 10% for the on-corridor inventory; it was below 2% for the entire 18
years for the on-corridor inventory. This difference is not surprising since the impact of posting
an on-corridor bridge would be much more significant than a posting of an off-corridor bridge.
The percentage of bridge that were posted decreased over time for both inventories. These
findings (greater fraction on the corridor versus off the corridor and a decrease over time) are
similar to what was observed for the macroview database. This result suggests that overall the
on-corridor bridges performed better than the off-corridor bridges.
4.3.9 Operationally “A” Posted Bridges
Presented in Figure 4.10 is the fraction of bridges with an operational posting of “A”, i.e., open
with no restrictions. This plot is effectively the inverse, or balance, of the results shown in
Figure 4.9. It is useful, however, to see clearly the fraction that were unrestricted, particularly
for the on-corridor inventory.
UDUTC Final Report
Page 65
% of Operationally "A" Posted BF Bridges
Percent of Total Bridges
105
% of A Oper. Posted, BF Bridges off corridor
% of A Oper. Posted, BF Bridges on corridor
100
95
90
85
80
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 4.10 Percentages of microview bridges posted “A” (Open, no restriction)
The results show that the on-corridor inventory performed better than the off-corridor
inventory, having a much higher fraction of bridges with no restrictions. The on-corridor
inventory had over 98% of the bridges with no restrictions during that time, and this
approached 100% in some years. By comparison, the off-corridor inventory had at most 90%
with no restriction, but did improve over the years.
4.3.10 Operationally “P” Posted Bridges
Presented in Figure 4.11 are the fraction of bridges with an operational posting of “P”, i.e., were
posted because of a restricted load limit less than the state legal load.
% of Operationally "P" Posted BF Bridges
Percent of Total Bridges
14
% of P Oper. Posted, BF Bridges off corridor
% of P Oper. Posted, BF Bridges on corridor
12
10
8
6
4
2
0
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
UDUTC Final Report
Page 66
Figure 4.11 Percentages of microview bridges posted “P” (Posted for load)
The percentages shown in Figure 4.11 represented a portion of the total occurrence of bridges
which had a deficiency-indicating type code (Figure 4.9). The off-corridor bridges showed a
decrease in the occurrence of bridges posted for load between 1992 and 2009. Such a marked
decrease in load-posted bridges indicated the performance had improved for the bridges not
on the microview corridor. The on-corridor microview bridges showed a different trend in
performance. The on-corridor structures historically had very low incidences of interstate
bridges posted for load. Figure 4.11 shows the low values for on-corridor bridges. Incidence of
bridges posted for load was an average 0.09% (0.0009), and never exceeded 0.33% (0.0033).
This showed a remarkably low occurrence of load postings for the interstate bridges on the
microview corridor.
Stated another way, and comparing Figure 4.9 and Figure 4.11, one can see that a majority of
the postings off of the corridor are due to limited load (type “P”), whereas the majority of
postings on the corridor, while very small, are due to something other than limited load (some
type other than “P” or “A”).
4.3.11 Bridges Posted for Load
Presented in Figure 4.12 is a column plot of the fraction of bridges posted for load, as identified
by item 70 – Bridge Posting. As described earlier in Chapter 3, the difference between the data
items is item 41 only indicates that a bridge has been posted, whereas item 70 classifies the
level to which the bridge was posted. This item applied a type code to posted bridges to
indicate the allowable load level of the posting. This quantitative appraisal of a bridge’s posting
indicates how much load a bridge could legally carry. Figure 4.12 shows the percentages of
bridges that were assigned a type code between “4” (0.1-9.9% below the legal limit) and “0”
((>39.9% below the legal limit) for Item 70 – Bridge Posting.
UDUTC Final Report
Page 67
% Posted BF Bridges
Percent of Total Bridges
14
% Posted, BF Bridges off corridor
% Posted, BF Bridges on corridor
12
10
8
6
4
2
0
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 4.12 Percentages of load postings of microview bridges on- and off-corridor
Consistent with the results shown in Figure 4.11, the fraction of bridges with a load posting is
much higher for the off-corridor inventory than for the on-corridor inventory. The fraction did
decrease over time for the off-corridor inventory, but varied over the same period for the oncorridor inventory. The consistently low levels of posted on-corridor bridges indicated positive
performance for the on-corridor/interstate bridges. Both on- and off-corridor groups
experienced a “spike” in the percentages of posted bridges in 1998; accounting for this sudden
increase was difficult, and an explanation for this spike could not be determined.
Once again, as discussed previously in Chapter 3, one might expect the plots in Figure 4.11 and
Figure 4.12 to be identical; differences, however, can be noted. The differences are due to the
way the data was originally coded by the states.
The results for the microview are similar to that of the macroview (Figure 3.12), with the
exception that the fraction of posted bridges on-corridor in the microview was significantly less
than that seen for the macroview database.
4.3.12 Condition Ratings
Presented in Figure 4.13, Figure 4.14, and Figure 4.15 are the average deck, superstructure, and
substructure condition ratings for the 18 year period. As was observed in the macroview
comparison, the ratings for the on-corridor inventory are consistently greater than those for
the off-corridor inventory. Once again, this suggests better overall condition/performance of
the on-corridor group. The average deck and substructure condition rating for the on-corridor
group varied between approximately 6.25 and 6.5 for the entire time, which corresponds to
satisfactory condition. The average superstructure rating is greater than 6.5 for most of the 18
UDUTC Final Report
Page 68
years. Note, however, that the average superstructure and substructure ratings for the oncorridor group decrease slightly between 1992 and 2009, which does indicate a slow
degradation in performance over time. The average ratings for the off-corridor group vary
between 6 and 6.5 the entire time, and show a slight increase after 1999.
Average Deck Condition Ratings, BF Bridges
Average Deck Rating
7
6.5
6
Cond. Rating, BF Bridges off
corridor
5.5
5
Cond. Rating, BF Bridges on
corridor
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 4.13 Average deck condition ratings for microview bridges on- and off-corridor
UDUTC Final Report
Page 69
Average Superstructure Condition
Ratings, BF Bridges
Average Superstructure Rating
7
6.5
6
Cond. Rating, BF Bridges off
corridor
5.5
5
Cond. Rating, BF Bridges on
corridor
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 4.14 Average superstructure condition ratings for microview bridges on- and offcorridor
Average Substructure Condition
Ratings, BF Bridges
Average Substructure Rating
7
6.5
6
Cond. Rating, BF Bridges off
corridor
5.5
5
Cond. Rating, BF Bridges on
corridor
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 4.15 Average substructure condition ratings for microview bridges on- and off-corridor
UDUTC Final Report
Page 70
4.3.13 Normalized Operating Rating
Presented in Figure 4.16 is the average Normalized Operating Rating for the microview
inventory. Normalized values above 1.0 were greater than 32.4 metric tons.
Normalized Operating Ratings, BF Bridges
Rating, normalized for MS18 (32.4 metric tons)
2.4
2.2
2
1.8
1.6
Op. Rat., BF Bridges off corridor
Op. Rat., BF Bridges on corridor
1.4
1.2
1
0.8
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 4.16 Average normalized operating ratings of microview bridges on- and off-corridor
The average normalized operating ratings were above 1 for both groups over the entire 18 year
period. The average for the on-corridor was consistently higher than that of the off-corridor
inventory. Both increased gradually over the 18 year time period. If operating rating is an
indication of performance, than the on-corridor inventory in general performed better or was
in better condition than the off-corridor inventory. And the condition of both inventories
gradually improved over time.
4.3.14 Normalized Inventory Rating
Figure 4.17 shows the yearly average values for microview bridges’ normalized inventory
ratings. Similar to the operating rating, the inventory rating was normalized by the MS18 design
truck load of 32.4 metric tons. Normalized inventory rating values greater than 1.0 indicate
positive performance.
UDUTC Final Report
Page 71
Normalized Inventory Ratings, BF Bridges
Rating, normalized for MS18 (32.4 metric tons)
1.4
1.3
1.2
1.1
1
Inv. Rat., BF Bridges off corridor
Inv. Rat., BF Bridges on corridor
0.9
0.8
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 4.17 Average normalized inventory ratings of microview bridges on- and off-corridor
The average normalized inventory rating of the on-corridor bridges was always greater than
1.0, was always greater than the off-corridor average, and increased gradually over time. The
average normalized inventory rating for off-corridor was less than 1.0 until 1997 when it
exceeded 1.0, but also gradually increased over time. Here again, the fact that the average
rating on-corridor was consistently higher than the off-corridor average indicates a better
overall condition of the on-corridor inventory.
The results shown here are clearly different compared to the macroview results (Figure 3.14), in
which there was no clear difference between the on-corridor and off-corridor views.
4.3.15 Average Posted Roadway Area
Figure 4.18 shows the yearly average posted roadway areas. Bridge roadway areas contributed
to this measure only if Item 70 – Bridge Posting was between “4” and “0”, meaning the bridge
was posted for load.
UDUTC Final Report
Page 72
Average Posted Roadway Area, BF Bridges
Average Posted Roadway Area (m2)
9,000
8,000
7,000
6,000
Posted Roadway Area, BF Bridges off corridor
Posted Roadway Area, BF Bridges on corridor
5,000
4,000
3,000
2,000
1,000
0
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 4.18 Average posted roadway areas of microview bridges on- and off-corridor
The average roadway area of posted bridges on the corridor was consistently greater than that
of the bridges off of the corridor. Between 1992 and 1995 the difference was significant. It was
discovered that these large values were the result of contributions from a very small number of
load-posted bridge records. During this time, no more than 30 bridge records were responsible
for the on-corridor posted bridge area values; the highest contribution to which this
corresponded was 0.77% (0.0077) of all yearly bridge records. The reason for the large posted
roadway areas was the sheer size of the posted bridges that were posted. In 1995, the largest
posted roadway area was 56,944 m2 (612,940 ft2), which was equivalent to more than 14 acres
of bridge area; this was observed for a bridge with an Item 70 – Bridge Posting type code of “4,”
which meant the bridge’s operating rating was not more than 10% below the state maximum
allowable load level. From 1996 on, the average on-corridor area was 3 to 9 times the offcorridor posted roadway area. The average off-corridor remained fairly constant over the entire
18 year period; after 1996 the average on-corridor varied between 1300 m2 and 1900 m2.
4.3.16 Estimated Total Posted Roadway Area
Similar to the method used to estimate the total roadway area, the total posted roadway area
was estimated. Table 4.5 shows the number of records for posted bridges for each year, and
the percentage of the years’ records that were deemed “blank” due to missing information.
UDUTC Final Report
Page 73
Table 4.5 Blank entries in calculating roadway area of posted on-and off-corridor microview
bridges
Year
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
On-Corridor Bridges
Records
Blanks
% Blank
31
1
3.23
28
2
7.14
16
1
6.25
18
4
22.22
48
16
33.33
43
25
58.14
122
1
0.82
47
1
2.13
41
0
0
36
0
0
26
0
0
26
0
0
17
0
0
6
0
0
11
0
0
21
0
0
20
0
0
24
0
0
Off-Corridor Bridges
Records
Blanks
% Blank
4,057
55
1.36
3,876
62
1.60
3,188
58
1.82
3,130
51
1.63
3,035
58
1.91
2,929
75
2.56
3,829
90
2.35
3,069
68
2.22
2,885
56
1.94
2,789
62
2.22
2,657
61
2.30
2,604
69
2.65
2,582
55
2.13
2,416
53
2.19
2,351
69
2.93
2,317
74
3.19
2,250
67
2.98
2,199
64
2.91
The percentages of records missing data in the off-corridor group varied between 1.4% and
3.2%, a small fraction; therefore, the estimated total posted roadway area for it should be
accurate. The percentages of records missing data in the on-corridor group was much more
variable, with a low of 0% for all years after 2000, and a high of 58% missing in 1997. The
overall fraction, however, is still less than 10%. Figure 4.19 shows the estimated total posted
roadway area for microview inventories.
UDUTC Final Report
Page 74
Calculated Total Posted Roadway Area (million m2)
Estimated Total Posted Roadway Area, BF Bridges
1.4
1.2
1
0.8
Calculated Total Posted Roadway Area, BF Bridges off corridor
Calculated Total Posted Roadway Area, BF Bridges on corridor
0.6
0.4
0.2
0
92
93
94
95
96
97
98
99
00
01
02
03
04
05
06
07
08
09
Year
Figure 4.19 Estimated total posted roadway areas of microview bridges on- and off-corridor
The total posted area off-corridor was consistently greater than the area on the corridor, by a
factor of about 5. However, the total posted roadway area for both groups decreased over
time, indicating a general improvement in condition of the inventory over time. The total area
off of the corridor decreased at a faster rate then that of the on-corridor inventory.
The “spikes” in the off-corridor trend line can be attributed to two separate causes: an
atypically high average posted roadway area in 1993, and an atypically high number of bridge
records in 1998. These two factors resulted in correspondingly high values for the total
roadway areas. The causes for these outliers could not be determined from the NBI data.
4.4 Summary of Findings for Microview Corridor
The Microview BOSFOLK database compared performance data for two groups of BOSFOLK
bridges. Bridges defined as on-corridor were those which carried interstate highway routes and
other major highways that intersect or are near I-95. The off-corridor bridge group consisted of
the macroview on-corridor database, minus all of the microview on-corridor bridges. The
microview database was mapped by selecting state counties that were adjacent to I-95 and the
other on-corridor interstate routes. Table 4.6 shows a concise summary of the parameter
comparisons made between the on- and off-corridor inventories. The key findings and
conclusions from the analysis of the microview database are as follows:
UDUTC Final Report
Page 75
1. The number of bridges in the on-corridor inventory was significantly less than the
number in off-corridor inventory. The number in the off-corridor inventory increased
slightly over time; however, the number in the on-corridor inventory remained about
the same.
2. The average age of bridges off of the corridor was greater than the age of those on the
corridor. The average age of both groups increased over time; the rate of increase was
slightly faster for the on-corridor group than for the off-corridor group. The average age
of neither group in 2009 was above 50 years old, the typical design life of a bridge in
these inventories.
3. The average roadway area of the bridges on the corridor was almost 4 times the
average area of the bridges off of the corridor. This shows that the on-corridor bridges
are on average larger (longer and/or wider) than the off-corridor bridges. The average
areas remained nearly constant for both groups over the 18 year period. The estimated
total roadway area for the off corridor group was approximately twice that of the oncorridor group. Thus while the number of bridges off of the corridor was approximately
6 times the number on the corridor, the total area was only twice that of the on-corridor
group.
4. Once again, as would be expected, the general traffic and truck traffic on the bridges on
the corridor was much greater than on the bridges off of the corridor. The ADT on the
corridor was about 4 times greater than that off of the corridor. Likewise, the truck
traffic was also much greater on the corridor than off of the corridor. Higher traffic
volumes imply a larger number of load cycles and a larger number of high load cycles for
the on-corridor bridges, as compared to the off-corridor bridges. Thus there is clearly
higher demand on the on-corridor bridges than there is on the off-corridor bridges.
5. The average sufficiency rating of the bridges on the corridor was greater than that of the
bridges off of the corridor, over the entire 18 year period. The average sufficiency rating
of the on-corridor inventory was above 80% for almost the entire 18 years. This
indicates better overall condition of the on-corridor inventory compared to the offcorridor inventory.
6. The on-corridor group had significantly fewer posted bridges, of any type, compared to
the off-corridor bridges: the on-corridor group had fewer than 2% of its bridges posted
for load in 17 of 18 years. This too suggests a better overall condition state for the oncorridor inventory as compared to the off-corridor inventory. The number of posted
bridges off of the corridor decreased over the 18 year period, indicating a gradual
improvement in the overall condition, but still not at the same level as the on-corridor
group.
7. The average condition ratings of the on-corridor group were consistently higher (better)
than the off-corridor group. This suggests better overall condition of the on-corridor
UDUTC Final Report
Page 76
group versus than the off-corridor group. The average superstructure and substructure
ratings for the on-corridor group did decrease slightly over time, indicating a slow
degradation in performance. The average condition ratings of both groups fall between
the satisfactory and good ranges.
8. The on-corridor average operating and inventory ratings were consistently greater than
the off-corridor ratings, indicating greater load carrying capacity on average by the oncorridor inventory. Both ratings increased over time, indicating a general overall
improvement of both groups over time.
9. The percentage of posted bridges off of the corridor decreased from 1992 to 2009,
indicating an overall improvement of condition of the off corridor inventory in that
regard. The fraction of posted on-corridor bridges was much more variable, but
significantly lower than the fraction off of the corridor.
10. The average posted roadway area of the on-corridor bridges was more than twice that
of the off-corridor bridges, for many of the years (it was much greater than that during
the early years but this is believed to be due a few very large posted bridges during
those years). However, the total posted roadway area of the off-corridor inventory was
approximately 5 times that of the on-corridor group. The total posted roadway area
decreased over time for both groups, indicating a gradual improvement of condition of
the both inventories.
Table 4.6 Summary comparison of microview results
Parameter
Number of bridges
Age
Average roadway area
Total roadway area
ADT
ADTT
SR
# posted
Condition ratings
Operating rating
Inventory rating
Average posted roadway area
Total posted roadway area
On-corridor
On
On
On (4x)
On
On (4-5x)
On (4-5x)
On
On
On
On
On
On (2x)
On
<<
<
>
<
>>
>>
>
<<
>
>
>
>
<<
Off-corridor
Off (5x)
Off
Off
Off (2x)
Off
Off
Off
Off
Off
Off
Off
Off
Off (5x)
In summary, the microview analysis revealed that the on-corridor inventory of bridges was
younger and significantly smaller, but aging at a faster rate than the off-corridor inventory. The
average roadway area of the on-corridor bridges is substantially larger than that of the average
UDUTC Final Report
Page 77
off-corridor bridge; however, the total bridge roadway area is greater off of the corridor. As was
observed for the macroview, the traffic on the corridor was significantly higher than off of the
corridor. Implied with this higher traffic are more load cycles and more heavy load cycles on the
corridor versus off of the corridor. However, by all of the tangible performance measures,
which includes sufficiency rating, postings, condition ratings, operating and inventory ratings,
the on-corridor inventory performed better than the off-corridor inventory. Thus, while there
was more demand on the on-corridor inventory, the inventory performed better overall, than
the off-corridor inventory. Some performance factors for the on-corridor inventory increased
over time, indicating a general overall improvement of the condition of the inventory; two
condition ratings decreased slightly over time, indicating a general decline in performance.
UDUTC Final Report
Page 78
5 Summary and Conclusions
Results of an investigation have been presented, the objective of which was to investigate and
assess the resiliency of the bridges on the BOSFOLK corridor. This was done through a
systematic analysis of historical data from the National Bridge Inventory. Two different
perspectives were taken in the analysis – the macroview perspective and the microview
perspective. The BOSFOLK corridor was defined in very broad terms in the macroview
perspective and included almost all of the bridges in the 11 states and DC that encompass the
BOSFOLK corridor. The microview perspective of the corridor was defined much more
specifically by the route of Interstate 95 and the other major roads and highways that connect
to it. In each instance databases were created from NBI data for the years 1992 through 2009.
The databases were then split into bridges on the corridor, and bridges off the corridor.
Descriptive parameters and performance parameters from the NBI were selected. The NBI data
files were then downloaded, filtered, and queried to create the final four databases. The
databases were then imported into Microsoft Excel for analysis and plotting. The results were
analyzed and presented in the form of timeline and column plots that illustrated the
performance over time.
Based on this analysis the following conclusions can be stated:
1. The macroview analysis revealed that the on-corridor inventory of bridges, while
somewhat fewer in number and older than the off-corridor inventory, accounted for
more bridge roadway area and was exposed to higher traffic volumes than the offcorridor inventory. However, by most of the tangible performance measures the oncorridor inventory performed better than the off-corridor inventory. Thus, while there
was more demand on the on-corridor inventory, the inventory performed better overall,
than the off-corridor inventory. Based on the macroview perspective, the bridges on the
corridor were more resilient than the bridges off of the corridor.
2. The macroview analysis showed that the performance of both inventories either
improved or remained about the same during the 18 year period, indicating general
overall improvement of the entire inventory over time.
3. The microview analysis revealed that the on-corridor inventory of bridges was younger,
smaller in number, but aging at a faster rate than the off-corridor inventory. The
average roadway area of the on-corridor bridges is substantially larger than that of the
average off-corridor bridge; however, the total bridge roadway area is greater off of the
corridor. The traffic on the corridor was significantly higher than off of the corridor.
Implied with this higher traffic are more load cycles and more heavy load cycles on the
corridor versus off of the corridor. However, by all of the tangible performance
measures, the on-corridor inventory performed better than the off-corridor inventory.
Thus, while there was more demand on the on-corridor inventory, the inventory
UDUTC Final Report
Page 79
performed better overall, than the off-corridor inventory. Based on the microview
perspective, the bridges on the corridor were more resilient than the bridges off of the
corridor.
4. Both the macroview and the microview perspectives provided evidence that bridges on
the corridor are exposed to more traffic, which implies more load cycles and more
heavy load cycles than for the bridges off of the corridor. However, in both instances the
on-corridor inventory has performed better than the off-corridor inventory. Thus, while
they both appear to be resilient, the on-corridor bridges have fared better and the thus
one can say were more resilient than the off corridor bridges.
Note that this study did not consider or take into account things such as differences in
maintenance practices of the states, different environmental and weather conditions, state
specific policies and practices, or allocation of funding and resources to the states. All of these
factors in some way have an impact on the long-term performance of the nation’s bridge
inventory. The NBI does not provide any information related to these issues that can be used to
correlate to the performance measures. Additional work would need to be conducted, and data
beyond the NBI collected, in order to study the correlation between performance and these
factors.
Results have been presented that show or would suggest an “improvement” in the overall or
average condition of the on-corridor or off-corridor inventories. It should be noted that an
apparent improvement could be due to any number of factors, such as – new bridges being
added to the inventory that are in better condition, older bridges being taken out of service, or
repairs being made to bridges that would change their posting level, condition ratings, or
operating and inventory ratings. No effort has been made to determine the cause for the
improvement from the NBI data, as this was viewed to be beyond the scope of this project, but
could be something for future work.
UDUTC Final Report
Page 80
Acknowledgements
The authors would like to thank the University of Delaware University Transportation Center for
the supporting this research.
References
1. Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation’s
Bridges, 1995, Federal Highway Administration, Report No. FHWA-PD-96-001,
Washington, DC 20590
2. Dunker, K. F., & Rabbat, B. G. (1990). Highway bridge type and performance patterns.
Journal of Performance of Constructed Facilities, 4(3), 161-173.
3. Farhey, D. N. (2006). Deficient bridge mobility performance measures. Advances in
Structural Engineering, 9(5), 603-610. ILL
4. Farhey, D. N. (2010). Performance of bridge materials by structural deficiency analysis.
Journal of Performance of Constructed Facilities, 24(4), 345-352.
5. Farhey, D. N. (2011). Operational structural performances of bridge types. Journal of
Performance of Constructed Facilities, 25(6), 554-563.
6. Farhey, D. N. (2012). Operational structural performances of bridge materials by areas.
Journal of Performance of Constructed Facilities, 26(4), 453-461.
7. Farhey, D. N. (2013). Operational structural performance of bridge types by areas.
Journal of Performance of Constructed Facilities, 27(3), 303-318.
8. Lee, S. (2012). Current state of bridge deterioration in the US-part 1. Materials
Performance, 51(1), 62-67.
9. Li, Z., & Burgueno, R. (2010). Using soft computing to analyze inspection results for
bridge evaluation and management. Journal of Bridge Engineering, 15(4), 430-438.
10. Sun, X., Zhang, Z., Wang, R., Wang, X., & Chapman, J. (2004). Analysis of past national
bridge inventory ratings for predicting bridge system preservation needs. Maintenance
and Management of Pavement and Structures, (1866), 36-43. Also TRR TE7.A1 H53
11. Tabatabai, H., Tabatabai, M., & Lee, C. (2011). Reliability of bridge decks in Wisconsin.
Journal of Bridge Engineering, 16(1), 53-62.
UDUTC Final Report
Page 81