1. Report No.
2. Government Accession No.
3. Recipient's Catalog No.
FHWA/OH-2008/14
4. Title and subtitle
5. Report Date
Crash Base Rates for Freeways/Reduction Strategies for Rear End
Crashes - Volume 2: Reduction Strategies for Rear End Crashes in
Ohio
January 2009
7. Author(s)
8. Performing Organization Report No.
6. Performing Organization Code
Prahlad D. Pant, Ph.D.
Subarna Panta
10. Work Unit No. (TRAIS)
9. Performing Organization Name and Address
PDP Associates Inc.
P.O. Box 888264
Atlanta, GA 30356
11. Contract or Grant No.
134230
13. Type of Report and Period Covered
12. Sponsoring Agency Name and Address
Ohio Department of Transportation
1980 West Broad Street
Columbus, Ohio 43223
14. Sponsoring Agency Code
15. Supplementary Notes
16. Abstract
The primary objective of this research was to systematically review past studies on rear end crashes,
examine strategies for reducing rear end crashes on both freeway and non freeway facilities, and develop a
set of rear end crash reduction strategies for use in Ohio, which will be appropriate for various traffic
engineering solutions, operations and ITS improvements. Accordingly, this study conducted an extensive
review of past literature related to rear end crashes and strategies to reduce them. A determination of
specific strategies for a road safety improvement program requires an understanding of probable crash
reduction capabilities for various geometric, operational and environmental factors on the roadways.
Studies of crash reduction strategies have usually focused on before-and-after comparisons of specific
locations or conditions. Based on the data provided by the Ohio Department of Transportation, this study
attempted to examine the crash reduction capabilities for signalized intersections, unsignalized
intersections, freeways and non-freeways where countermeasures were implemented. An attempt was made
to compute crash reduction factors for rear end collisions for these roadway facilities. However, this task
could not be performed because of the severe limitations in the ODOT countermeasure and roadway site
data. In response to the researchers’ request for additional data, ODOT decided not to proceed ahead with
this research as it required the dedication of district resources that were not currently available. It was
believed that breaking the project into smaller, more manageable pieces, would not yield results that would
be statistically significant. There were also several national projects underway which would limit this
project’s benefits. In view of these circumstances, ODOT decided to terminate the contract for this project
and all work stopped.
17. Key Words
18. Distribution Statement
Rear End Crashes, Rear End Accidents, Crash Base Rate,
Accident Base Rate, Freeways, Crash Density, Crash Rate,
Accident Density, Accident Rate.
No restrictions. This document is available to
the public through the National Technical
Information Service, Springfield, Virginia 22161
19. Security Classif. (of this report)
20. Security Classif. (of this page)
Unclassified
Unclassified
21. No. of Pages
Form DOT F 1700.7 (8-72)
Reproduction of completed pages authorized
22. Price
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2
Crash Base Rates for Freeways/Reduction Strategies for Rear End Crashes
Volume 2: Reduction Strategies for Rear End Crashes in Ohio
Prepared by
Prahlad D. Pant, Ph.D.
Principal Investigator
and
Subarna Panta
Systems Analyst
Research Performed By
PDP Associates Inc.
P.O.Box 888264
Atlanta, GA 30356
Research Performed Under
State Job No.: 134230
Agreement No.: 20819
Prepared in cooperation with
Ohio Department of Transportation
and
U.S. Department of Transportation,
Federal Highway Administration.
January 2009
3
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4
Disclaimer Statement
The contents of this report reflect the views of the authors who are responsible for the facts
and accuracy of the data presented herein. The contents do not necessarily reflect the official
views or policies of the Ohio Department of Transportation or the Federal Highway
Administration. This report does not constitute a standard, specification, or regulation.
5
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6
ACKNOWLEDGEMENT
The researchers thank the following officials of the Ohio Department of Transportation for
their assistance in the conduct of this research study.
• Ms. Monique Evans P.E., Administrator, Office of Research & Development;
• Ms. Jennifer Townley P.E., Administrator, Office of Systems Planning and Program
Management;
• Mr. Don P. Fisher P.E., Manager, Office of Systems Planning and Program
Management;
• Mr. Jonathan Hughes P.E., Manager, Office of Systems Planning and Program
Management;
• Mr. Tom Ramsay, Office of Systems Planning and Program Management
7
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8
TABLE OF CONTENTS
1.0 Statement of the problem
-
-
-
- 15
2.0 Objectives
-
-
-
- 19
3.0 Background and Significance of work
-
-
-
- 21
4.0 Further Review of Crash Reduction Factors
with Medium to High Level of Predictive
Certainty for Rear End Collision Reduction
Strategies
-
-
-
- 35
5.0 Possible Causes of Rear End Crashes
and their Reduction Strategies
5.1 Possible Causes of Rear-End Crashes
5.2 Reduction Strategies for Rear-End Crashes -
-
-
- 37
- 37
- 38
6.0 Data Collection and Analysis
6.1 Data Collection
6.2 Data Compilation
6.3 Request for Data
-
-
-
- 49
- 49
- 49
- 53
7.0 Conclusions
-
-
-
- 57
Reference
-
-
-
- 59
Appendix I Simple Before and After Comparison Appendix II AID Tree Diagram for
Rear End Crashes
-
-
-
- 63
-
-
- 85
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10
LIST OF TABLES
Table 1. Rear End Crashes in Ohio from 1998 – 2007
…………………….. 15
Table 2. Rear End Crash reduction Factors – Ohio 1997
…………………….. 16
Table 3. Reduction Strategies for Rear End Crashes at Signalized
Intersections
…………………….. 39
Table 4. Reduction Strategies for Rear End Crashes at Unsignalized
Intersections
…………………….. 42
Table 5. Reduction Strategies for Rear End Crashes at NonFreeways
…………………….. 44
Table 6. Reduction Strategies for Rear End Crashes at Freeways
…………………….. 46
Table 7. Simple Before Study for Countermeasures employed on
intersections in year 2004
…………………….. 50
Table 8. Countermeasures Listed in ODOT Data
…………………….. 54
Table 1.1: Simple Before and After Comparison for
Countermeasures employed in Intersections from year 2001 – 2004
…………………….. 65
Table 1.2: Simple Before and After Comparison for
Countermeasures employed in Interstate from year 2001 – 2004
…………………….. 67
Table 1.3: Simple Before and After Comparison for
Countermeasures employed in Non-Interstate from year 2001 –
2004.
…………………….. 71
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12
LIST OF FIGURES
Figure 1. AID Tree diagram for rear end accident density for
all 12 districts of rural highways without intersection.
…………………….. 89
Figure 2. AID Tree diagram for intersections With One Way
Stop Sign - No Control Legs - Rear end Crashes
…………………….. 90
Figure 3. AID Tree diagram for T Intersections with One Way
Stop Sign - Stop Control Legs - Rear end Crashes
…………………….. 91
Figure 4. AID Tree diagram for Two Way Stop Control
Intersections- No Control Legs - Rear end Crashes
…………………….. 91
Figure 5. AID Tree diagram for Two Way Stop Control
Intersections- Stop Control Legs - Rear end Crashes
…………………….. 92
Figure 6. AID Tree diagram for Flashing Beacon Control
Intersections- No Control Legs - Rear end Crashes
…………………….. 92
Figure 7. is for AID Tree diagram For Flashing Beacon
Control Intersections- Stop Control Legs - Rear end Crashes
…………………….. 93
Figure 8. AID Tree diagram for Signalized Intersection Legs Rear end Crashes
…………………….. 94
Figure 9.AID Tree diagram for rear end accident density for
statewide freeways.
…………………….. 95
Figure 10. AID Tree diagram for rear end accident rate for
statewide freeways.
…………………….. 96
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14
VOLUME 2. REDUCTION STRATEGIES FOR REAR END CRASHES
1.0
Statement of the Problem
The US Department of Transportation reports that 5.97 million crashes occurred in the
United States in 2006 (1). The damages and injuries from these crashes cost the United States
billions of dollars each year. A Federal Highway Administration (FHWA) publication
indicates the cost of crashes at 230 billion dollars each year (2). The National Highway
Traffic Safety Administration (NHTSA) 2003 General Estimates System data suggests rear
end crashes at 28 percent of the total crashes (3).
The Ohio Department of Public Safety has reported that a total of 328,742 traffic accidents
occurred in 2007. Of these, 87,976 or 26.76 percent of the total accidents were rear end
collisions. Statistics show that the proportion of the rear end collision to the total traffic
accident has remained almost constant over the last ten years. The data for rear end crashes
over the last decade is given below (4).
Table 1: Rear End Crashes in Ohio from 1998 - 2007
Year
Total
Crashes
Rear End
Collision
Percentage of
Rear End
Collision
2007
328,742
87,976
26.76
2006
334,206
90,933
27.21
2005
358,127
94,077
26.27
2004
381,639
101,682
26.64
2003
392,683
102,199
26.03
2002
386,076
101,619
26.32
2001
387,075
102,714
26.54
2000
386,122
100,410
26.00
1999
385,704
103,445
26.82
1998
377,920
102,871
27.22
(Source- Traffic Crash Facts, Ohio Department of Public Safety,
http://www.publicsafety.ohio.gov/crashes/crash_facts.asp)
A conference presentation titled “Strategies for Improving Safety and Mobility on Ohio
Roads” points out that 43 percent of all freeway crashes occur on 12.5 percent of the freeway
system and 19.4 percent of all non-freeway crashes occur on 1.9 percent of the non- freeway
system. It also indicates that 31.3 percent of freeway rear end crashes occur on 4.3 percent of
the freeway system (5). Ohio DOT aims to reduce the total number of crashes 10 percent by
2010 and reduce rear end collision 25 percent by the year 2010 (6 ).
15
The Safety Core Business Unit of the Federal Highway Administration conducted a program
review of the Highway Safety Improvement Program in six states (Delaware, Oregon,
Connecticut, Florida, Ohio and Iowa) during 2001.The findings related to crash reduction
factors are as follows:
• Oregon extensively used customized crash reduction factors.
• Connecticut used both cost/benefit analysis and crash reduction factors in selecting
projects for implementation.
• Two districts of Florida DOT that were visited, used statewide crash reduction factors
to perform benefit/cost analysis (7).
• Ohio ranks second to California in terms of safety funding (6, 7).
In 1997, ODOT identified 12 crash reduction factors related to rear end crashes which are
shown in the table below (8).
Table 2: Rear End Crash reduction Factors – Ohio 1997
No.
1
2
3
4
5
6
7
8
9
10
11
12
Description
Lane use signs – overhead
Install PTSWF sign/flasher[for approach speeds > 45 mph]
Widen pavement to provide 2WLTL
Install left turn bay & extra pavement without signal
Install left turn bay & extra pavement with signal
Widen for left turn lane, including resurfacing
Widen for right turn lane, including resurfacing
Install traffic signal - all types
Add left turn phase with new left turn lane
Add left turn phase with existing left turn lane
Install optically programmed heads
Relocate driveway entrance
CRF
0.1
0.6
0.2
0.2
0.2
0.2
0.2
-0.1
0.2
0.1
0.1
0.2
A safety study generally focuses on “analysis of roadway and traffic related data to determine
the possible cause of identified crash pattern and provide alternative countermeasures to
mitigate the crash patterns” (10). For safety studies, ODOT uses crash data for a minimum of
three years. The crash data is reviewed for the following crash characteristics of a site and a
detailed analysis is done to identify the problems and their possible causes.
1. Crash Type - Angle, Backing, Fixed Object, Sideswipe, Head-On, Rear End
2. Time of Day – Day, Night
3. Pavement Condition –Wet, Dry
4. Severity – PDO, Injury/Fatalities
After possible causes are identified, every alternative measure of improvement including “do
nothing” is analyzed. The rate of return is calculated, which “determines the benefit expected
16
to be obtained by the improvements (10).” Crash reduction factors are used in computing the
rate of return for both PDO and Injury/Fatalities crashes. A user friendly Excel worksheet is
developed for this purpose (11). However, currently ODOT does not have a uniform and
complete set of statewide strategies for reducing rear end crashes.
17
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18
2.0
Objectives:
The primary objective of this research study is to systematically review past studies on rear
end crashes, examine strategies for reducing rear end crashes on both freeway and non
freeway facilities, and develop a set of rear end crash reduction strategies for use in Ohio,
which will be appropriate for various traffic engineering solutions, operations and ITS
improvements. The study was designed to perform the following tasks to fulfill the
objectives.
1. Conduct a thorough review of literature.
2. Obtain crash, traffic and roadway inventory data from ODOT, and prepare a master
database for use in this study.
3. Analyze the above mentioned ODOT data and determine crash reduction factors for
rear end collision reduction strategies.
4. Prepare a set of strategies for reducing rear end collisions and provide appropriate
recommendations.
19
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20
3.0
Background and Significance of Work
Different strategies could be adopted for cost effective safety improvements in all types of
roadways. Determination of specific countermeasures for the road safety improvement
program requires an understanding of probable crash reduction capabilities for various
geometric, operational and environmental factors on all types of roadways. Crash Reduction
Factors (CRFs) are such tools that many agencies use to estimate cost effective
countermeasures for safety improvement programs.
Crash reduction factors (CRFs) are used to determine probable crash reduction capabilities
for various geometric, operational and environmental factors associated with specific
improvements on different types of roadways including freeways, non-freeways and
signalized and unsignalized intersections. Studies of crash reduction factors have usually
focused on before-and-after comparisons of specific locations or conditions.
This research effort has conducted an extensive review of past literature related to rear end
crashes. The review of past literature includes countermeasures for the reduction of rear end
collisions, causes of rear end crashes and crash reduction factors related to rear end crashes.
One such research paper titled “Attention Based Model of Driver Performance in Rear End
Collisions” published in 2000 in the Transportation Research Record focuses on the attention
based model of driver performance in rear end collisions (12). This paper attempted to
introduce an attention based rear end collision avoidance model “that describes the driver’s
attention distribution, information extraction and judgment process”. The paper indicated that
the model components “provide a structure for interpreting conflicting reaction-time data and
also provide several important recommendations for the design of warning algorithms and
displays.”
Another research paper titled “Analysis of Design Attributes and Crashes on the Oregon
Highway System”, and published in August 2001, explores the relationship between crash
occurrence and roadway design characteristics (13). Studies were performed on both freeway
and non freeway roadway facilities that were located on both urban and rural areas. The
study findings indicated that numerous design characteristics and crash occurrence were
statistically related.
Another research paper titled, “Taking Tire Slip Ratio into Account and Estimating Friction
Coefficients in Rear-End Collisions on Winter Roads” was published in the Transportation
Research Record in 2001 (14). The primary focus of the study was to estimate the road
surface friction coefficient in rear end collisions on winter road conditions in Japan. The
study indicated that the friction ratio is dependent on tire slip ratio, particularly of a specific
type of tire and also attempted to evaluate the relationship between improvement in traffic
safety and increment in friction coefficient. The findings of the study suggested that
accidents could be reduced by improving winter road conditions and increasing the friction
coefficient. The study indicated that the rate of accidents in icy road conditions decreased by
21
50 percent if the friction coefficient increased by 0.1. The study, however, concluded that
more research is required to obtain most favorable friction coefficient threshold.
Another research paper titled “Rear-End Collision–Warning System Design and Evaluation
via Simulation” focuses on a rear end collision warning system that is built in a vehicle
(15). A rear end collision warning system was designed and evaluated. In this system, a lead
vehicle is able to warn the following vehicle if the later is coming close too rapidly. A
warning algorithm was developed based on an appropriate warning distance. The factors
considered, while designing the algorithm were minimizing the occurrence and severity of
crashes and reducing the frequency of nuisance alarms. The findings showed that it was
possible to design an effective rear end collision system which could minimize the
occurrence and severity of crashes. The study recommended field studies to derive optimum
values for design parameters.
The Crash Reduction Information approved by the North Carolina DOT in 2002 (16) shows
the following countermeasures listed for rear end crashes:
ƒ New traffic signal
ƒ Closed loop signal system
ƒ Left turn lane at intersection
ƒ Right turn lane at intersection
ƒ Increase turn lane length
ƒ Continuous left turn lane
ƒ Widening for additional lane
ƒ Vertical realignment
ƒ Improve skew angle
ƒ Skid treatment
ƒ Remove traffic signal
ƒ Dynamic message sign
A research paper related to crash reduction factors, titled “Development of Crash Reduction
Factors: Methods, Problems, and Research Needs” was presented at the 82nd annual meeting
of the Transportation Research Board in 2003 (17). This paper examined the method,
problems and research needs for the development of crash reduction factors. The emphasis
was placed on the before-and-after study method as it is the predominant method of choice
for development of crash reduction factors. The paper introduced and reviewed three
different before-and-after methods:
ƒ The simple before-and-after method,
ƒ The before-and-after study with comparison group method, and
ƒ The before-and-after study with the empirical Bayes method.
A paper titled “Configuration Analysis of Two-Vehicle Rear-End Crashes” was presented at
the 82nd annual meeting of the Transportation Research Board in Washington D.C on Jan 1216, 2003 (18). This paper examined the role of light trucks in rear-end accidents. Light
trucks are vehicles bigger and heavier than passenger cars and are more likely to affect the
visibility of the passenger car driver. The study indicated that due to distraction and limited
22
visibility there is a higher chance of rear end crashes when a regular passenger car follows a
light truck vehicle.
A paper titled “Driver Attributes and Rear-End Crash Involvement Propensity” was
published by the National Highway Traffic Safety Administration (NHTSA) in March 2003
(19). This study explores statistical relationship between the crashes and the drivers who are
involved in crashes. The primary sources of information for this study were General
Estimates Systems (GES) and the Fatality Analysis Reporting System (FARS), both
compiled by the National Highway Traffic Safety Administration (NHTSA). The findings of
this study suggested a strong statistical relationship between the sex of the driver and the type
of rear end crash and also between the age of the driver and the type of rear end crash. Some
of the inferences made by the studies are:
ƒ Drivers under 18 have highest rate of rear end striking crashes.
ƒ Probability of striking rear end crashes decreases with age.
ƒ Young male drivers are more likely to be involved in rear end crashes than young
female drivers.
Another research paper titled “Examination of Crash Contributing Factors Using National
Crash Databases” was published in October 2003 (20). This study was prepared by the
National Highway Traffic Safety Administration (NHTSA) to examine the factors that
contribute to some specific types of vehicle crashes. The research was based on crash data
obtained from various sources. The research was divided into three phases.
a) Phase one - comparison of the contributing factor distributions from different data sources
in order to assess which database contains more information about the selected factors.
b) Phase two – investigation of the issues of crash severity to see if the contributing factors
varied depending on the severity of the crash.
c) Phase three - determination of the contributing factors based on the pre-crash scenarios for
each crash type.
The findings included analysis of three different scenarios – single vehicle off road, lane
change and rear end crashes. Inattention, alcohol/drugs, and speeding were found to be the
major factors for all types of crashes. In the rear end crash analysis, three different scenarios
were selected – lead vehicle decelerating, lead vehicle moving and lead vehicle stopping. The
crash contributing factors for the later two scenarios were similar to all types of crashes.
Inattention and speeding were the top two primary contributing factors for both scenarios.
Findings from the rear end crash scenario analysis suggested that alcohol and drugs were
higher contributing factors for the lead vehicle moving than the lead vehicle decelerating and
lead vehicle stopping scenarios. Rear end collisions were found to be more likely to occur in
situations involving the lead vehicle moving when the driver of the striking vehicle was
under the influence of alcohol/drugs rather than if the striking vehicle was speeding.
Intersections
A project on development of crash reduction factors was done by Kentucky Transportation
Institute in 1996 (21). This study was primarily based on surveys of other states that were
using some form of crash reduction factors. This study extensively used data provided by 37
states. It indicated that 19 states had developed their own accident reduction factors and that
23
18 states used reduction factors developed by other states. Based on the survey and review of
past literature, this study recommended nine groups of accident reduction factors. The study
also listed percent reduction of accidents for certain types of improvements. The reported
improvement category for intersection that are related to rear end crashes are:
ƒ Channelization of left –turn lanes at no-signal intersection
ƒ Additional left turn at signalized intersection
ƒ Additional left –turn lanes at no-signal intersection
A report titled “Strategic Highway Safety Plan for Vermont” published in December 2001
(22) states its goal to minimize the occurrence and severity of crashes by identifying and
implementing achievable and effective education, enforcement, engineering and emergency
response initiatives. The report focuses on seven critical emphasis areas and has identified
specific crash reduction strategies for each of them. The critical emphasis areas are as
follows:
ƒ Keeping vehicles on the roadway and minimizing the consequences of leaving the
road
ƒ Young drivers
ƒ Improving the design and operation of highway interactions
ƒ Increasing seat belt use and improving airbag effectiveness
ƒ Reduced impaired driving
ƒ Curbing speeding and aggressive driving
ƒ Keeping drivers alert
The crash reduction strategies listed in the fourth critical emphasis area also targets the rear
end crashes which occur in the intersections. The following strategies are listed in this area:
ƒ Improve visibility by providing enhanced signing and delineations
ƒ Improve maintenance and visibility of signs and markings
ƒ Improve geometry at intersections
ƒ Implement physical changes on the approaches to and at intersections
ƒ Improve driver compliance with traffic control devices and traffic laws at
intersections through increased enforcement
ƒ Reduce speed at intersections
ƒ Increase public awareness at High Crash Locations
ƒ Implement a local program for identifying and prioritizing High Crash Locations
NCHRP Synthesis 310, Impact of Red Light Camera Enforcement on Crash Experience A
Synthesis of Highway Practice was published in 2003 (23). The primary objective of this
synthesis was to determine the impact of red light camera on crashes and their severity. The
findings of the research suggest that the red light cameras could bring about slight increase in
the rear end crashes and decrease in angle crashes. The synthesis however, cautions that more
research is needed to reach a conclusive finding.
NCHRP Report 500, Guidance for Implementation of the AASTHO Strategic Highway
Safety Plan was published in 2003 (24). Volume 5 of this report outlines guidelines for
addressing unsignalized intersection collisions and Volume 12 deals with the signalized
intersection collisions. Intersections represent only a small part of the overall roadway
system but intersection related crashes account for more than 50 of all crashes in urban areas
24
and 20 percent in the rural areas. Rear end crashes constitute 6 percent of the crashes at
signalized intersection and 1 percent at unsignalized intersection. Most of the objectives of
this guidance relate to the physical improvement of signalized and unsignalized intersections.
Though the strategies relate to all type of crashes many strategies are appropriate for rear end
crashes. The guidance “provides a classification of strategies according to the expected time
frame and relative cost.” The guidance also provides description of strategies and classifies
the strategies into three types – proven, tried and experimental. Many of the strategies relate
to rear end crashes.
A research study titled “An Evaluation of Red Light Camera (Photo-Red) Enforcement
Programs in Virginia: A Report in Response to a Request by Virginia’s Secretary of
Transportation” and published in 2005 (25) focused on seven Virginia red light camera
programs. The researchers claim that there was a ‘definite’ increase in rear end crashes after
red light cameras were installed. The study also confirms that there was an increase in total
injury after the camera was installed.
A focus group study titled “Driver Attitudes and Behaviors at Intersections and Potential
Effectiveness of Engineering Countermeasures” was published in 2005 (26). This research
effort focused on identifying driver attitudes and behaviors with respect to four different
intersection scenarios including rear end crashes. The engineering countermeasures discussed
are intersection rumble strip and improved skid resistance or a combination of both.
The report “Update of Florida Crash Reduction Factors and Countermeasures to Improve the
Development of District Safety improvement Projects” was published in April, 2005 (27).
The main objective of this study was to update the Florida DOT’s CRFs “and to develop a
computer system to systematically maintain safety improvement projects implemented by its
districts to facilitate regular CRF updates” The study also conducted survey of state DOTs.
The improvement programs for rear end crashes being utilized by various DOTs include
ƒ Channelization intersection
ƒ Painted Lane
ƒ Protected lane with curb or raised bars
ƒ Install two-way left-turn lane in median
ƒ Channelize two-lane to three lane
ƒ Channelize four lane to five lane
ƒ Add left and right turning lanes with signal
ƒ Provide right-turn lane
ƒ Add left turn lane with physical separation
ƒ Add left turn lane with painted separation
ƒ Add turning lanes
ƒ Add double left turn lanes
ƒ Add T-intersection turn and bypass lane
ƒ Detached left-turn lane
ƒ Increase turning radii
ƒ Improve sight distance
ƒ Change all way stop sign from two-way stop sign
ƒ Install lane use sign
25
ƒ
ƒ
Remove unwarranted signal
Install flashing beacon
Though most DOTs have used simple before-and-after and cross sectional methods for
developing CRFs, this research study used Empirical Bayes method to overcome a statistical
vulnerability. Crash reduction Analysis System Hub(CRASH), a web-based application
system was developed as a part of this research effort to allow recording and maintaining
projects, updating CRFs based on the latest available improvement project and crash data and
applying CRFs in the benefit-cost analyses of specific projects.
A research results digest 299 titled “Crash Reduction Factors for Traffic Engineering and
Intelligent Transportation System (ITS) Improvements: State of Knowledge Report” was
published in November 2005 by NCHRP (28). This digest provides an overview of the
current status of the crash reduction factors for a variety of treatments and provides an
outline of the “best available” crash reduction factors. This digest uses AMF (Accident
Modification Factors) as the standard terminology as a means of being uniform with other
continuing researches being done by NCHRP. AMFs or CMFs (Crash Modification Factors)
are expressed as (1 – CRF). A CRF of 10% would be equal to 0.90 AMF. “CRFs are the
quantitative results from research studies, indicating the percentage reduction in crashes that
can be expected after implementing a treatment or program. AMF are derived from crash
reduction factors and are used in predictive technologies to estimate the reduction of crashes
that can be expected for a specific treatment or installation.”
The report emphasizes the importance of AMFs in the decision making process of the states
and addresses the “ impediments that prevent more extensive use of AMFs” which affects
the quality of the factors which is being used by many states. The issues addressed in the
report are:
ƒ Origins/Transferability of AMFs
ƒ Methodological issues
ƒ Variability
ƒ Crash Migration and spillover issue
ƒ Lack of information in effectiveness
ƒ Combinations of treatments
ƒ Publication/Citation issues
This digest lists 100 specific treatments which include both traditional and ITS
countermeasures. Out of these 100 treatments 20 were found to be credible with high to
medium level of predictive certainty. This digest gives a summary of the research study from
which the AMF was developed. The crash reduction strategies that were included in the
summaries of the research studies that developed AMFs for intersections and which are
related to the rear end crashes are follows:
ƒ Install roundabout
ƒ Add exclusive left-turn lane
ƒ Add exclusive right-turn lane
ƒ Install a traffic signal
ƒ Remove a traffic signal
ƒ Modify signal change interval
26
ƒ
ƒ
Convert to all-way stop control
Install red light camera
The final report of this project will include a comprehensive summary of the best AMFs that
are available at that time.
A research study titled “Update and Enhancement of ODOT's Crash Reduction Factors” was
published in June 2006 (29). The main objective of this study was to update the list of crash
reduction factors for Oregon Department of Transportation. ODOT has been using the
current list of countermeasures since early 1990’s. The study lists the three distinct types of
countermeasures and their crash reduction factors:
1. which are backed by robust research
2. with limited research and
3. discussion only (no research)
The countermeasures include design improvements, Operations/ITS and markings and signs.
The listed countermeasures for intersection that are backed by robust research and that relate
to rear end crashes are:
ƒ Add left-turn-bay, signalized intersection
ƒ Add left-turn-bay, unsignalized intersection
ƒ Add right-turn lane on major road, signalized intersection
ƒ Add right-turn lane on major road, unsignalized intersection
ƒ Add two way left turn lane
ƒ Install automated enforcement of red light violations
ƒ Lengthen the yellow change interval to ITE guidelines
ƒ Remove traffic signal from one way street
The countermeasures include design improvements, Operations/ITS and markings and signs.
The listed countermeasures for intersection with limited research and that relate to rear end
crashes are:
ƒ Convert 4-lane into 3-lane
ƒ Improve intersection sight distance/clear sight triangles
ƒ Provide illumination for intersection
The Illinois Department of Transportation has published a Highway Safety Improvement
Program under Illinois Comprehensive Highway Safety Plan. The program includes
Guidelines to Counter Measure Effectiveness & Crash Reduction Factor effective November
2006 (30). The countermeasures and CRFs that concern intersection rear end crashes are
ƒ Channelization
ƒ Lane Addition Left turn Lane,
ƒ Right Turn Lane Bidirectional
ƒ Install roundabout,
ƒ Overhead sign tuss,
ƒ Advance warning signs,
ƒ Signal modernization,
ƒ Advance warning with flasher,
ƒ Add traffic actuation,
ƒ Curb Parking removal.
27
Freeways
A project on development of crash reduction factors was done by Kentucky Transportation
Institute in 1996 (21). This study was primarily based on surveys of other states that were
using some form of crash reduction factors. This study extensively used data provided by 37
states. It indicated that 19 states had developed their own accident reduction factors and that
18 states used reduction factors developed by other states. Based on the survey and review of
past literature, this study recommended nine groups of accident reduction factors. The study
also listed percent reduction of accidents for certain types of improvements. The
improvement category related to for all types of crashes in the freeway are:
ƒ Construct interchange
ƒ Modify Entrance/Exit Ramp
ƒ Frontage Road
ƒ Glare Screen for night accidents
The countermeasures include design improvements, Operations/ITS and markings and signs.
The listed countermeasures for freeway with limited research and that relate to rear end
crashes are:
ƒ Provide illumination on highway sections
ƒ Install ramp metering
ƒ Provide illumination for freeway
A research study titled “Advance Warning of Stopped Traffic on Freeways: Current Practices
and Field Studies of Queue Propagation Speeds” was published by the Texas Transportation
Institute in June 2003 (31). This study focused on the following three major causes of
slow/stopped traffic conditions:
ƒ Congestion related to recurrent traffic conditions
ƒ Congestion related to work zones
ƒ Congestion related to incidents
The following significant findings related to rear ends collision are summarized in the report.
ƒ Most frequent type of collision in the United States especially at work zones is rearend collisions
ƒ Rear-end crashes on freeways are caused by normal speed traffic encountering
slow/stopped traffic on main lanes or ramps
The following significant findings related to driver behavior approaching slow/stopped traffic
are summarized in the report
ƒ Hard braking maneuvers between 1 and 16 per 1000 approaching vehicles observed at
two work zone sites.
ƒ 5% of vehicles rapidly approached end of queue despite advance warning
The study summarizes several studies that claims to have estimated the benefits of advance
warning of slow/stopped traffic on freeways
ƒ 0.5 seconds of an additional warning time of slow/stopped vehicle could reduce rear
end collisions by 60 % and an extra second of warning time could reduce rear end
collisions by as much as 90%.
28
ƒ
Queue warning systems in Netherlands, Germany and England were found to
significantly lower the rate of rear end collisions on freeways
A report titled “Advance Warning of Stopped Traffic on Freeways: Field Studies of
Congestion Warning Signs” was published by the Texas Transportation Institute On March
2005 (32). This research study addresses a major safety concern leading to rear end
collisions on freeways, which is traffic flowing at normal speed encountering unexpected
slow or stopped traffic. The main objective of this study in the first phase was to conduct a
literature review to determine current practices for advance warning for stopped traffic and in
the second phase was to test two advance warning techniques using static warning signs on
the Dallas area freeway. The research study identified the following four basic problem areas
where advance warning of slow of stopped traffic are recommended.
ƒ Sight distance constraints
ƒ Recurrent congestion
ƒ Construction/maintenance zones
ƒ Incidents
The research study observes that no standard for advance warning exists and further studies
are needed to address other areas including, desirable messages for various conditions and
assessment of the prevalence of rear-end crashes where congestion and horizontal or vertical
alignment visibility constraints exist.
The Research Results Digest 299 titled “Crash Reduction Factors for Traffic Engineering and
Intelligent Transportation System (ITS) Improvements: State of Knowledge Report”
published in November 2005 by NCHRP (28) and discussed earlier under the section of
Intersection lists two countermeasures exclusively for freeways for all types of crashes with
medium-high predictive certainty. They are:
ƒ Narrow lane widths to add lanes (applicable to urban freeway)
ƒ Add shoulder rumble strips (applicable to both rural and urban freeway)
The digest mentions that no AMF exists for safety service patrol, which has become a very
common countermeasure on many freeways as a way to reduce incidents and secondary
crashes.
The final report of this project will include a comprehensive summary of the best AMFs that
are available at that time.
A research titled “A Comprehensive Analysis of the Relationship between Real-Time Traffic
Surveillance Data and Rear-End Crashes on Freeways” was prepared for the presentation at
the TRB 2006 annual meeting (33). This paper attempts to develop a strategy to identify realtime traffic conditions prone to rear-end crashes using freeway loop detector data. The paper
concludes that the rear end crashes may be grouped into two different segments/groups. The
first group consists of rear end crashes that occur under extended congestion and the second
group of crashes occurs with relatively free-flow conditions prevailing 5-10 minutes before
the crash. The data comparison between two different groups revealed that group one crashes
was associated with extended congestion indicated by high occupancy while group two
crashes were associated with downstream speed differential and downstream on ramp traffic.
The paper claims that 75 percent of the rear end crashes may be identified 5-10 minutes
before their occurrence
29
The University of Minnesota published a report titled “Identification and Simulation of a
Common Freeway Accident Mechanism: Collective Responsibility in Freeway Rear-end
Collisions” in April 2006 (34). In this study the researchers have obtained trajectory
information of vehicles involved in rear end crash from video records. These trajectories
were used to ascertain each driver’s speed, following distance, reaction time and braking rate.
The researchers claim to have simulated what would have happened if certain driver reaction
had been different, other variables remaining constant. The researchers claim to have
established the following findings:
“1. Short following headways by the colliding drivers were probable casual factors for the
collisions,
2. for each collision at least one driver ahead of the colliding vehicles probably had a reaction
time that was longer than his or her following headway, and
3. had the driver’s reaction time been equal to his or her following headway, the rear-end
collision probably would not have happened.”
A research study titled” Modeling the Probability of Freeway Rear-End Crash Occurrence’
published June 2006 (35) claims to have developed a model of freeway rear-end crash risk
based on a modified negative binomial regression. The model considers a drivers response
time distribution and applies a dual-impact structure accounting for the probability of a
vehicle becoming an obstacle and the following vehicle’s reaction failure. The findings of
this study include:
ƒ Higher VMT which is a generalized AADT was found to decrease the probability of a
leading vehicle becoming an obstacle
ƒ Higher truck percentage per mile was found increase the probability of lead vehicle
becoming an obstacle
ƒ Higher posted speed limit was found to decrease the probability of rear end collisions
ƒ Narrow shoulder width was found to increase the probability of rear end crashes
ƒ Probability of rear end crash is higher in the merge sections of the freeways.
A research study titled “Update and Enhancement of ODOT's Crash reduction Factors” was
published in June 2006 (31). The main objective of this study was to update the list of crash
reduction factors for Oregon Department of Transportation. ODOT has been using the
current list of countermeasures since early 1990’s. The study lists the three distinct types of
countermeasures and their crash reduction factors:
1. which are backed by robust research
2. with limited research and
3. discussion only (no research)
The Illinois DOT’s Guidelines to Counter Measure Effectiveness & Crash Reduction Factor
effective November 2006 (29) has listed Raised Reflective Markers as countermeasure for
nighttime freeway crashes of all types. The CRF is negative for ADT less than 20000 and is
positive for ADT greater that 20000
30
Ohio
The Ohio Department of Transportation’s countermeasure effectiveness reduction factor was
published in September, 1997, which was later revised in July, 2007 (9). The
countermeasures for rear end crashes are listed as follows:
ƒ Lane use signs – overhead
ƒ Install PTSWF sign/flasher [for approach speeds > 45 mph]
ƒ Install left turn bay & extra pavement without signal
ƒ Install left turn bay & extra pavement with signal
ƒ Widen for left turn lane, including resurfacing
ƒ Widen for right turn lane, including resurfacing
ƒ Add left turn phase with new left turn lane
ƒ Add left turn phase with existing left turn lane
ƒ Install optically programmed heads
ƒ Relocate driveway entrance
All the above listed had positive crash reduction factors for rear end crashes. The
countermeasure - Install traffic signal - all types, had a negative crash reduction factor for
rear end crashes though it was positive for other types of crashes
Ohio Department of transportation published “Development of Crash Reduction Factors” in
September 2005 (36). The report states that the main objective of the research effort was to
develop CRFs for the seven types of improvements ranked by the ODOT as most important.
They are as follows:
ƒ Add two-way left turn lane
ƒ Install median barriers
ƒ Remove/relocate fixed object
ƒ Flatten slope, remove guardrail
ƒ Flatten vertical curve
ƒ Provide interchange lighting
ƒ Close median opening
The CRFs were computed for only total crashes and injury/fatal crashes for all the above
types of countermeasures. Rear end crashes were not specifically considered.
The Ohio Department of Transportation, in an effort to develop a set of reliable base crash
rates initiated a research project in 1998 with the University of Cincinnati. The study was
titled “Rational Schedule of Base Accident Rates for rural Highways in Ohio, Phase I” (37).
The researchers successfully developed a set of mathematical models to estimate base
accident density/rate for non-intersections in rural highways in ODOT District 8. Phase II
study (38) was completed in 2003 to develop a set of mathematical models to estimate base
accident density/rate for non-intersections in rural highways in the remaining eleven ODOT
districts. Crash base rate were developed for density and rate of different types of crashes
including rear end crashes. Appropriate dependent variables were used in the development of
the base rates. AID technique was employed in identifying a set of independent variables that
had significant relationship with each dependent variable. The studies recommended means
and standard deviations for each type of accidents type to be used as the method for
31
calculating cash base rate. Regression equation was also developed in each of the research
study which could be used as an additional tool for predicting the crash base rate. The results
showed a strong relationship between rear end crash density and ADT. A small number of
rear end crashes were also found to be associated with speed and population density. The
AID tree is given in Appendix II.
Another study to develop a set of mathematical models to estimate base crash rates for
intersections in Ohio has been completed in December 2006(39). This study also employed
similar methodologies that were used in the study to develop crash base rate for rural
highways. Crash density was calculated for different types of intersections. A summary of
the results showing the relationship between rear end crash density for different types of
intersections and the independent variables is as follows:
ƒ Intersections With One Way Stop Sign - No Control Legs: Strong relationship
between rear end crash density and ADT. A small number of rear end crashes were
also found to be associated with number of left and through lanes
ƒ T Intersections with One Way Stop Sign - Stop Controlled Legs: Strong relationship
between rear end crash density and ADT.
ƒ Two Way Stop Control Intersections- No Control Legs: Strong relationship between
rear end crash density and ADT.
ƒ Two Way Stop Control Intersections- Stop Controlled Legs: Strong relationship
between rear end crash density and ADT.
ƒ Flashing Beacon Control Intersections- No Control Legs: Strong relationship
between rear end crash density and ADT.
ƒ For Flashing Beacon Control Intersections- Stop Controlled Legs: Strong
relationship between rear end crash density and ADT.
ƒ Signalized Intersection Legs: Strong relationship between rear end crash density and
ADT.
The AID Trees for each of the above mentioned intersections is given in Appendix II.
Another research study to develop a set of crash base rate for freeways was completed in
March 2007 (40). This study also employed similar methodologies that were used in the
study to develop crash base rates for rural highways and intersections.
The result showed a strong relationship between statewide freeway rear end crash density
and ADT. A small number of rear end crash densities were also found to be associated with
distance to interchange. Similarly, The result showed that a strong relationship existed
between statewide freeway rear end crash rate and population density. A small number of
rear end crash rate were also found to be associated with distance to interchange.
The AID trees for statewide rear end crash density and rate are given in Appendix II.
Summary
Significant amount of research has been performed to understand rear end crashes on
different types of roadways. Behavioral variables such as driver inattention influence of drug
and alcohol, aggressive driving have been attributed to rear end crashes. Geometric and
32
design variables such as number of lanes, curve characteristics, vertical grade, surface type,
median type, turning lanes, shoulder width, lane width have been ascribed to have significant
relationship with rear end crashes. Operation characteristics such as traffic control, red light
camera, visibility of signs and markings have been recognized as having strong association
with rear end crashes. Other roadway characteristics such as high congestion, work zones,
slow or stopped traffic due to incidents also are found to have strong correlation with
occurrence of rear end crashes.
Several reduction strategies/factors exist, that address behavioral, geometric and design and
operations characteristics of rear end crashes in different types of roadways such as
intersections, rural and urban freeways and rural and urban highways. The condition of every
state and every roadway segment within a state is inimitable. At the same time changes in
roadway conditions could be very rapid. Many of the strategies that are being implemented
by several agencies have been proven to have a high or medium level of certainty. There are
also ongoing researches that look promising. Those strategies need to be examined and
recommended if they are found compatible with the overall rear end collision strategy in
Ohio.
33
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34
4.0
Further Review of Crash Reduction Factors with Medium to High
Level of Predictive Certainty for Rear End Collision Reduction
Strategies
The NCHRP Report 617 titled “Accident Modification Factors for Traffic Engineering and
ITS improvements” published in 2008 includes a comprehensive summary of the best AMFs
that are available (41).
“Remove a traffic signal” is one of the specific treatments with high level of predictive
certainty for rear end crashes at intersections. The AMF for all types of crashes is calculated
at 0.76 and the AMF for rear end crashes is calculated at 0.71 (41).
Another specific treatment that has medium-high level of predictive certainty for different
types of crashes which includes rear-end crash is “Convert to All-Way Stop Control.” The
AMF for rear end crashes is 0.87 (41).
“Add Exclusive left turn lanes” and “Add Exclusive right turn lanes” are two treatments that
are defined as high level of AMF predictive certainty. This study does not specifically
discuss about the percent reduction in rear end crashes or AMFs for rear end crashes.
Numerous previous studies have indicated that rear end crashes constitute a high percentage
of intersection crashes. The treatment discussed in this study, therefore could be as useful for
rear end crashes. Further research targeted specific to rear end crashes may be warranted to
gain a better insight.
The AMFs given for different types of geometry for left-and right-turn crashes are as
follows:
Left-Turn Crashes:
One
Approach
Both
Approaches
Rural Stop-Controlled Intersection (4-legs)
Rural Stop-Controlled Intersection (3-legs)
Rural Signalized Intersection (4-legs)
Rural Signalized Intersection (3-legs)
Urban Stop-Controlled Intersection (4-legs)
Urban Stop-Controlled Intersection (3-legs)
Urban Signalized Intersection (4-legs)
Urban Signalized Intersection (3-legs)
0.72
0.56
0.82
0.85
0.73
0.67
0.90
0.93
0.52
—
0.67
—
0.53
0.86
0.96
0.74
0.92
0.81
Right Turn Crashes:
Rural Stop-Controlled Intersection (4-legs)
Urban Signalized Intersection (4-legs)
35
Fatal and Injury Intersection Accidents (all accident types)
Rural Stop-Controlled Intersection (4-legs)
Urban Signalized Intersection (4-legs)
0.77
0.91
0.59
0.83
“Install Roundabouts” is another treatment that is defined as high level AMF predictive
certainty. The AMFs for all types of accidents are calculated as followings:
Roadway Type
Single Lane - Urban (prior control – two way stop control)
Single Lane - Rural (prior control – two way stop control)
Multilane – Urban (prior control – stop sign)
Single/Multilane – Urban (prior control - signal)
All sites All Crashes
AMF
0.44
0.29
0.82
0.52
0.65
“Convert Stop- Control to Yield Control” is one of the specific treatments with high level of
predictive certainty for rear end crashes at intersections. The AMF for all types of crashes is
given at 2.37 (41).
“Install traffic signal at urban intersection” and “Install traffic signal at rural intersection” are
two of the specific treatments with high level of predictive certainty for rear end crashes at
intersections. The AMFs for “Install traffic signal at urban intersection” and “Install traffic
signal at rural intersection” are given at 1.50 and 1.58 respectively. (41).
“Install red light cameras” is another treatment with high level of predictive certainty. The
AMF for rear end crashes with all type of severity is given at 1.15 and AMF for rear end
crash with injury type severity is given at 1.24 (41).
36
5.0: Possible Causes of Rear End Crashes and Their Reduction Strategies
It seems that ODOT would greatly benefit if a “standard” set of possible causes of rear end
crashes and corresponding general reduction strategies for these crashes could be developed
and implemented on a statewide basis. Rear end crashes have exhibited different
characteristics in different types of roadways and the causes of rear end crashes for these
roadways may vary within a large number of contributing factors. Thus it is important to (a)
determine the possible cause(s) for rear end crashes for the roadway or intersection under
study and (b) to develop general strategies for reducing rear end crashes for each possible
cause. Based on the authors’ research (44), a list of possible causes for rear end collisions for
all types of roadways is provided below.
5.1
Possible Causes of Rear-End Crashes
• Absence of turning lanes
• Inadequate advance warning intersection warning signs
• Following too closely
• Crossing pedestrians
• Improper channelization
• Improper passing maneuvers
• Improper speed perception of right turning vehicles
• Inadequate delineation
• Inadequate directional guidance
• Inadequate shoulders/shoulder drop-off
• Insufficient left-turn storage length
• Large number of turning vehicles
• Lane drop
• Lack of adequate gaps
ƒ -for side road traffic
ƒ -for main line left turn
• Narrow lane width
• Obstruction in or too close to roadway
• Parking too close to intersection
• Pavement condition
• Restricted sight distance
• Slippery pavement
• Short turning radius
• Stop & start condition at slip ramps of yield- merge condition
• Drivers not aware of access points
• Uncontrolled access
• Yield sign control
• Improper/Illegal parking
ƒ Improper/absent signal coordination
• Railroad crossing
37
•
•
•
•
•
•
5.2
Inadequate intersection identification
Inadequate signal timing or phasing
Lack of dilemma zone protection
Poor visibility of signals
Truck drivers hesitant to stop
Unwarranted signal
Reduction Strategies for Rear End Crashes
Strategies for reducing rear end crashes can only be determined after possible causes of rear
end crashes for specific sites are identified. The highway facility under study can be
classified into the following groups:
1. Signalized intersections
2. Unsignalized intersections
3. Non-freeways and
4. Freeways
In the following tables, strategies for reducing rear end crashes are listed for each possible
cause of the crash for each highway facility as described above.
38
Table 3: Reduction Strategies for Rear End Crashes at Signalized Intersections
Possible Causes of Rear
End Crashes
Slippery pavement
Absence of Turning Lanes
Crossing pedestrians
Improper speed perception of
right turning vehicles
Improper/absent signal
coordination
Inadequate directional
guidance
Reduction Strategies for Rear End Crashes
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Inadequate intersection
identification
Inadequate signal timing or
phasing
Insufficient left-turn storage
length
Lack of dilemma zone
protection
Lack of improper vehicle
detection or malfunctioning
loop detectors
Large number of turning
vehicles
•
•
•
•
Overlay pavement
Provide adequate drainage
Groove pavement
Provide “slippery when wet” signs
Clean up road surface i.e. gravel, sand, soil, etc
Improve snow and ice control measures
Provide turning lanes
Increase turning radii
Install/improve signing or marking for pedestrian
crosswalks
Reroute/prohibit pedestrian traffic
Construct pedestrian bypass/overpass
Install heads and buttons if warranted
Install pedestrian phase
Prohibit/right turns on red from side streets
Install/Improve acceleration lane
Install/improve pavement markings
Coordinate signals
Optimize signal coordination
Install additional pavement markings(dotted
lines)/channel lines
Install/improve lane use control signs
Improve turn radii
Increase enforcement
Install/improve directional signing
•
•
•
Install/improve road name signs
Install advance road name signs
Adjust amber phase
Provide progression through a set of signalized
intersections, if available
Provide/adjust all-red clearance
Adjust signal timing or phasing
Lengthen left-turn storage
•
Provide dilemma zone protection
•
•
•
•
•
•
•
•
•
•
•
Relocate/modify vehicle detectors
Provide adequate maintenance of loop detectors
Install/improve dilemma zone loop detector configuration
Provide vehicle detection
Create left or right turn lanes
Prohibit turns
Increase turn radii
Provide special phase for turning traffic
Widen roadway
Channelize intersection
Retime signal
39
Poor visibility of signals
Restricted sight distance
Short turning radius
Stop & start condition at slip
ramps of yield- merge
condition
Truck drivers hesitant to stop
Unwarranted Signal
Improper channelization
Improper passing maneuvers
Inadequate advance warning
intersection warning signs
Inadequate delineation
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Provide turning guidelines
Provide dual turning lanes
Channelize intersection
Retime signal
Install/ improve advance warning signs
Install/improve overhead signals
Install/improve visors
Install/improve back plates
Relocate signals
Add additional signal heads
Remove obstacles
Provide flashers on advance warning devices
Use programmable heads
Provide dilemma zone protection
Adjust/re-aim signal head
Install higher watt signal
Remove obstacles
Provide adequate channelization
Provide phase for left turning traffic
Install/improve warning signs
Provide adequate sight distance
Restrict parking near intersection
Restrict/prohibit turns
Optimize stop bar placement to accommodate turning
traffic
Install supplemental heads
Provide adequate turning radii
Locate stop bars to accommodate turning traffic
Widen intersection
Install “Stop here on Red Signs”
Change to stop condition
Provide/improve acceleration lane
Remove ramp
Provide adequate roadway geometry
Provide/adjust dilemma zone protection
Add delay to side road detection to minimize frequency
of signal changing
Provide additional all red clearance
Remove signal
Improve channelization
Install/improve no-passing markings
Extend/modify existing passing zones
Increase enforcement
Install/upgrade warning signs
Install/upgrade advance intersection warning signs
Install flashers on advance warning devices
Optimize stop bar placement to accommodate turning
traffic
Install/improve raised pavement markers
Refurbish markings
Provide double-painting
Improve/install pavement markings
Install/upgrade delineation
40
Inadequate
shoulders/shoulder drop-off
Lane drop beyond
Intersection
Narrow lane width
Obstruction in or too close to
roadway
Parking too close to
intersection
Pavement condition
Uncontrolled access at
intersection
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Install/upgrade advance warning signs
Correct shoulder drop-off
Improve roadway shoulders
Install/improve advance warning signs(interim)
Drop lane at or before intersection
Add complete lane beyond intersection
Install/improve signing
Install improve pavement markings
Provide adequate lane width
Install/widen paved shoulder
Remove obstacles
Warn of obstructions
Mark obstructions
Install barrier curbing
Install breakaway features to light poles, sign post etc
Project objects with guard rail (if warranted)
Install crash cushioning device
Post parking restrictions near intersections
•
•
•
•
•
Perform road surface repair
Install warning sign (interim)
Eliminate, consolidate or relocate drives
Install service roads
Provide curb & gutter section to control/define access
points
Reduce width of access
•
41
Table 4: Reduction Strategies for Rear End Crashes at Unsignalized Intersections
Possible Causes of Rear
End Crashes
Absence of Turning Lanes
Crossing pedestrians
Improper channelization
Improper passing maneuvers
Improper speed perception of
right turning vehicles
Inadequate advance warning
intersection warning signs
Inadequate delineation
Inadequate directional
guidance
Inadequate
shoulders/shoulder drop-off
Insufficient left-turn storage
length
Lack of adequate gaps
-for side road traffic
-for main line left turn
Lane drop beyond
Intersection
Large number of turning
vehicles
Reduction Strategies for Rear End Crashes
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Provide turning lanes
Increase dual turning lanes
Install/improve additional signing
Improve horizontal/vertical alignment
Install/improve intersection control beacons
Install/improve road name signs
Improve sight distance and/or remove sight
obstruction(s)
Install/improve rumble strips
Install/improve street lighting
Improve channelization
Install/improve no-passing markings
Extend/modify existing passing zones
Increase enforcement
Install/upgrade warning signs
Install/Improve acceleration lane
Install/improve pavement markings
Install/upgrade advance intersection warning signs
Install flashers on advance warning devices
Optimize stop bar placement to accommodate turning
traffic
Install/improve raised pavement markers
Refurbish markings
Provide double-painting
Improve/install pavement markings
Install/upgrade delineation
Install/upgrade advance warning signs
Install/improve directional signing
Install additional pavement markings
Install/improve lane use control signs
Increase enforcement
Improve turn radii
Correct shoulder drop-off
Improve roadway shoulders
Install/improve advance warning signs (interim)
Lengthen left-turn storage
Improve lane use signs
Provide traffic signal if warranted
Provide multi-way stop signs
•
•
•
•
•
•
•
•
Drop lane at or before intersection
Add complete lane beyond intersection
Install/improve signing
Install improve pavement markings
Create left or right turn lanes
Prohibit turns
Increase turn radii
Provide traffic signal
•
•
•
•
•
•
•
•
•
•
•
•
42
Narrow lane width
Obstruction in or too close to
roadway
Parking too close to
intersection
Pavement condition
Restricted sight distance
Short turning radius
Slippery pavement
Stop & start condition at slip
ramps of yield- merge
condition
Uncontrolled access at
intersection
Yield Sign Control
•
•
•
•
•
•
•
•
•
•
•
•
•
Provide multi-way stop signs
Widen roadway
Channelize intersection
Provide adequate lane width
Install/widen paved shoulder
Remove obstacles
Warn of obstructions
Mark obstructions
Install barrier curbing
Install breakaway features to light poles, sign post etc
Project objects with guard rail(if warranted)
Install crash cushioning device
Post parking restrictions near intersections
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Perform road surface repair
Install warning sign (interim)
Remove obstacles
Provide adequate channelization
Install/improve active warning signs
Provide adequate sight distance
Restrict parking
Restrict/prohibit turns
Provide turn lanes
Provide adequate turning radii
Locate stop bars to accommodate turning traffic
Widen intersection
Overlay pavement
Provide adequate drainage
Groove pavement
Provide “slippery when wet” signs
Clean up road surface i.e. gravel, sand, soil, etc
Improve snow and ice control measures
Flatten steep grades
Change to stop condition
Provide/improve acceleration lane
Provide overlap phase
Remove ramp
Add right turn lane
Provide adequate roadway geometry
Eliminate, consolidate or relocate drives
Install service roads
Provide curb & gutter section to control/define access
points
Reduce width of access
Install stop signs
Change geometrics
Improve sight distance characteristics
•
•
•
•
43
Table 5: Reduction Strategies for Rear End Crashes at Non-Freeways
Possible Causes of Rear
End Crashes
Absence of Turning Lanes
Crossing pedestrians
Drivers not aware of access
points
Following too closely
Improper illegal parking
Improper/absent signal
coordination
Inadequate delineation
Uncontrolled access
Improper speed perception of
right turning vehicles
Inadequate
shoulders/shoulder drop-off
Lack of adequate gaps
-for side road traffic
-for main line left turn
Lane drop
Reduction Strategies for Rear End Crashes
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Provide turning lanes
Provide Two Way Left Turning Lane
Install/improve signing or marking for pedestrian
crosswalks
Reroute/prohibit pedestrian traffic
Construct pedestrian bypass/overpass
Install signal if warranted
Install/improve signing
Improve horizontal/vertical alignment
Install sight distance
Provide flashers on advance warning devices
Identify access points
Right in right out movements at access point
Close/relocate/consolidate drives
Driver education of safe driving practices –TV
commercials
Provide headway maintenance system
Increase capacity
Provide climbing lane
Increase enforcement
Prohibit parking
Create off street parking
Post parking restrictions
Coordinate signals
Optimize signal coordination
Improve/install pavement markings
Install/upgrade delineation
Install/upgrade advance warning signs
Optimize driveway stop bar placement to accommodate
turning traffic
Install/improve raised pavement markers
Refurbish markings
Provide double-painting
Close/ relocate drives
Provide curb & gutter section to control/define access
points
Reduce width of access
Install service roads
Install/Improve acceleration lane
Install/improve pavement markings
Correct shoulder drop-off
Improve roadway shoulders
Install/improve advance warning signs (interim)
Install/improve delineation
Provide traffic signal if warranted
Provide Lt lane or right side loop ramp at grade
separator
Drop lane at or before intersection
44
Large number of turning
vehicles
Narrow lane width
Railroad crossing
Restricted sight distance
Slippery pavement
Improper channelization
Improper passing maneuvers
Obstruction in or too close to
roadway
Pavement condition
Stop & start condition at slip
ramps of yield- merge
condition
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Add complete lane beyond intersection
Install/improve signing
Install improve pavement markings
Create left or right turn lanes
Prohibit turns
Increase turn radii
Change TWLTL to exclusive LT
Widen roadway
Provide adequate lane width
Install/widen paved shoulder
Lower speed limit
Advance warning of narrow lane
Install/improve warning signs
Provide adequate sight distance
Repair/replace crossing
Remove hump
Remove obstacles
Provide adequate channelization
Install/improve active warning signs
Provide adequate sight distance
Restrict parking near intersection
Restrict/prohibit turns
Optimize stop bar placement to accommodate turning
traffic
Overlay pavement
Provide adequate drainage
Groove pavement
Provide “slippery when wet” signs
Clean up road surface i.e. gravel, sand, soil, etc
Improve snow and ice control measures
Improve channelization
Install/improve no-passing markings
Extend/modify existing passing zones
Increase enforcement
Install/upgrade warning signs
Remove obstacles
Warn of obstructions
Mark obstructions
Install barrier curbing
Install breakaway features to light poles, sign post etc
Project objects with guard rail (if warranted)
Install crash cushioning device
Perform road surface repair
Install warning sign (interim)
Change to stop condition
Provide/improve acceleration lane
Provide overlap phase
Remove ramp
Add right turn lane
Provide adequate roadway geometry
45
Table 6: Reduction Strategies for Rear End Crashes at Freeways
Possible Causes of Rear
End Crashes
Drivers not aware of exit/entry
points
Following too closely
Inadequate delineation
Improper speed perception of
merging vehicles
Inadequate
shoulders/shoulder drop-off
Lack of adequate gaps
Large number of exiting
vehicles
Narrow lane width
Slippery pavement
Improper channelization
Pavement condition
Stop & start condition at slip
ramps of yield- merge
condition
Heavy congestion related to
recurrent traffic conditions,
incidents, or work zones
Improper perception of traffic
conditions at merge section of
Reduction Strategies for Rear End Crashes
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Install/improve signing
Improve horizontal/vertical alignment
Provide flashers on advance warning devices
Identify access points
Driver education of safe driving practices –TV
commercials
Provide headway maintenance system
Increase capacity
Provide climbing lane
Improve/install pavement markings
Install/upgrade delineation
Install/upgrade advance warning signs
Install/improve raised pavement markers
Refurbish markings
Provide double-painting
Install/Improve acceleration lane
Install/improve pavement markings
Correct shoulder drop-off
Improve roadway shoulders
Install/improve advance warning signs (interim)
Install/improve delineation
Provide ramp meters
Provide advance warning signs
Create left or right turn lanes
Increase turn radii
Widen roadway and exit ramps
Provide adequate lane width
Install/widen paved shoulder
Lower speed limit
Advance warning of narrow lane
Overlay pavement
Provide adequate drainage
Groove pavement
Provide “slippery when wet” signs
Clean up road surface i.e. gravel, sand, soil, etc
Improve snow and ice control measures
Improve channelization
Perform road surface repair
Install warning sign (interim)
Change to stop condition
Provide/improve acceleration lane
Remove ramp
Provide adequate roadway geometry
Provide advance real time traffic information
Provide advance warning signs with/without flashers
•
•
Provide advance real time traffic information
Install/Improve merge lane
46
freeway
Existence of vertical or
horizontal sight distance
constraint
Narrow shoulder width
•
•
•
•
Improve acceleration lane
Install ramp meter
Improve vertical or horizontal visibility/sight distance
Advance warning signs with/without flashers
•
Provide adequate shoulder width
47
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48
6.0: Data Collection and Analysis:
The primary objective of this task was to examine the required rear end crash data and the
data relating to countermeasures applied to signalized and unsignalized intersections,
freeways and non-freeways.
6.1: Data Collection:
At the request of the researchers, the Ohio DOT provided the following data:
1. Crash data (1997- 2006) – work zones were excluded.
2. Countermeasures completed at different types of roadways (1999 - 2004).
This study attempted to examine the above-mentioned data for all intersections, freeways and
non-freeways where the countermeasures were implemented.
6.2: Data Compilation:
The Excel file consisting of countermeasure data provided by ODOT contained both
individual and multiple countermeasures at roadway segments. Only sites with individual
countermeasures were chosen for this study as a review of past literature revealed (e.g.
NCHRP Research Digest 299) that no substantial research has yet been done on effect of
multiple countermeasures at a single location. The examination for the data was completed
in the following steps:
Task 1: The first task completed by the researchers was the separation of the rear end crash
data from the crash data of all types provided by the ODOT.
Task 2: The second task consisted of separating the rear end crash data for each year.
Task 3: During the third task, the rear end crash data was combined into intervals of three
year periods. For example, a single Microsoft Access file of combined rear end crash data
for 1997-1999 was created to analyze the “before” crash data for the countermeasures
completed in 2000. A single Microsoft Access file of combined rear end crash data for
2001-2003 was created to analyze the “after” crash data for the countermeasures completed
in 2000.
Task 4: The fourth task was to merge the “before” 3-year rear end crash data and “after” 3year rear end crash data with the rear end crash data for the corresponding year on which the
countermeasures were applied. Microsoft Access program, Structured Query Language and
Microsoft Excel were used.
Task 5: In the fifth task, the merged database was separated into three different subgroups:
intersections, freeways and non-freeways. A master file for each specific site on which the
countermeasure was implemented was created, which consisted of the “before” and “after”
rear end crash data for the year of implementation. An example of the master file for
countermeasures on interstate freeways implemented in 2004 is given in Table 7. A
complete set of the data is given in Appendix I.
49
Table 7. Simple Before Study for Countermeasures Employed on Intersections in 2004
Dist
NLF ID
Begin
Log
End
Log
Countermeasure
Before (# of
rear end
crashes 2002 and
2003)
2
4
SLUCIR00280**C
SSUMIR00076**C
4.91
10
5.1
12
7
SMOTIR00075**C
3.74
20.4
7
SMOTIR00075**C
10
12
8
SBUTIR00075**C
0
6.72
8
SHAMIR00071**C
7.53
8.03
8
SHAMIR00071**C
9.82
10.1
8
SHAMIR00071**C
12
14
8
SHAMIR00071**C
14
16
8
SHAMIR00071**C
16
18
8
SHAMIR00071**C
18
19.9
8
SHAMIR00074**C
5.73
6.26
8
SHAMIR00074**C
9.2
9.33
8
SHAMIR00074**C
16
18
8
SHAMIR00074**C
17.4
17.7
8
SHAMIR00074**C
18
18.8
8
SHAMIR00074**C
18.5
19
widen to six lanes
Extend channel line
for I-76 EB to I-77
SB ramp
2003 Added Thru75-Arrow
03 - Micro-surface
to correct skid
numbers.
Major widening PID
10751 and study
PID 75971 should
address issues
abb, Add signs on
Ramps and exit
panels
Add speed limit
signs
Rumble strips on
shoulders.
Rumble strips on
shoulders.
Rumble strips on
shoulders.
Rumble strips on
shoulders.
Signs/Turnarounds,
Signs up 7/13/99
PID 75730 to
reconstruct ramps
should address
issues
Rumble strips on
new pavement
PID 78082 ramp
meters should
address issues
PID 78082 to add
ramp meters
should address
issues
continue with
projects to redesign
interchange and
install ramp
metering
2
168
After (#
of rear
end
crashes
2005 and
2006)
0
173
100.00
-2.98
824
737
10.56
72
81
-12.50
453
352
22.30
21
23
-9.52
15
12
20.00
93
119
-27.96
186
183
1.61
180
97
46.11
187
141
24.60
2
2
0.00
2
3
-50.00
56
73
-30.36
10
10
0.00
34
33
2.94
52
44
15.38
Percent
Change
50
8
SHAMIR00074**C
19.2
19.5
8
SHAMIR00275**C
18.6
20.6
8
SHAMIR00275**C
23.4
29.8
8
SHAMIR00275**C
24
24.6
8
SHAMIR00275**C
30.7
31.6
8
SWARIR00075**C
10
12.2
12
SCUYIR00090**C
14.5
14.9
PID 76257 to
reconstruct
interchange and
PID 78082 to install
ramp meters
should address
issues
Remove unpaved
crossovers.
PID 77000 to
reconstruct ramps
should address
issues
widening project
PID 22386 should
address safety
issues
PID 20128 to add
aux lane from 42 to
RHH should
address issues
PID 10754
widening to the
MOT Co line
should address
issues
Install rumble strips
18
10
44.44
63
86
-36.51
499
375
24.85
60
69
-15.00
54
29
46.30
22
20
9.09
36
34
5.56
Task 6: This study attempted to perform comprehensive statistical tests for each file
consisting of the “before and “after” rear end crash data and countermeasures implemented at
the site. The objective of this task was to compute the crash reduction factors for rear end
collisions for these roadway facilities. However, this task could not be accurately performed
because of the limitations in the ODOT countermeasure data.
Before-and-after studies are primarily done for evaluating the effectiveness of
countermeasures and calculating crash reduction factors. Several Before-After designs are
available:
(1) Simple Before/After Design:
The basic before-and-after design is the Simple Before/After design. It evaluates a
situation before and after a countermeasure is implemented. This design is found to
have many drawbacks and is most often not used by safety researchers. The results,
particularly the crash reduction factors based on Simple Before/After Design, will
have low level of predictive certainty, if any, for collision strategies.
(2) Before/After with randomized control groups
In this design, sites with similar characteristics with likelihood of implementation of
countermeasures are assigned randomly to either control group or treatment group.
All the sites have thus, equal chance of falling into either of the groups. However, an
improvement measure is implemented only in the treatment group and no treatment is
done in the control group. Measurement before and after treatment is done in the
51
treatment group. Measurement before and after without treatment is done in the
control group and the results are evaluated. This design has been found to reduce
biasness and improve the accuracy of estimation.
(3) Before/After with comparison groups
The Before/After design with comparison group could be better suited to this study
since it could utilize ODOT historical data for roadway facilities where improvements
were completed in the past. The only difference between the preceding design and
this design is that the groups are not assigned on a random basis in this design. The
measurement criteria are the same. This design is more appealing and practical to this
study as sites with historical records (for example, ODOTs crash data for a particular
site) can be chosen even after countermeasures are implemented. The before and after
results in control groups are evaluated and compared with before and after results of
the treatment group. For each site that is selected for study, the traffic, roadway and
rear end crash data for 3 years prior to and 3 years after the improvement can be used
(42, 43). The roadways can be classified by different types, which include signalized
intersections, unsignalized intersections, non-freeways and freeways. The selection of
the sites can be based on the above criteria and can be grouped into control and
treatment groups. Data permitting, a sizable number of sites can be selected for each
group for minimizing statistical bias in the analysis.
Our examination of the ODOT data revealed that it was not possible to determine the
effectiveness of the countermeasures and calculate crash reduction factors by using the
Before/After Comparison Groups Design for several reasons:
1: In most case the countermeasures were not specific enough to be included in the study.
For example, the freeway countermeasures implemented in 2002 was follows:
• Add lanes
• Mill to improve skid resistance
• Epoxy pavement markings
• Improve Exit Ramp
• Enhance warning signs for exit loop ramp
• Interchange improvements
• Include Portable Message Board in construction plans to alert traffic to slower
moving traffic ahead
• Install YIELD sign for WB ramp
• Install 2 merge warning signs, relocate 3, install 1 Yield sign
• Section currently under total reconstruction
• Add Lane project to increase interstate capacity.
• Milled to improve skid resistance
• Improve signing and pavement markings
• Capacity addition
Another example of the intersection countermeasures employed in the year 2003 was as
follows:
• Rehabilitate roadway
52
•
•
•
•
•
•
Reconstruct intersection, installing LT lanes and RT lane and increasing approach
radii; Signal upgrade addition of turn phases.
New interchange
Construct offset LT lanes on SR82, LT lanes on SR7 and RT lane on SR7 SB
approach.
Widening and Increasing Intersection Radius
Replacing 2 Traffic Signals
Removal of parking on street
The above countermeasures are not uniform and lack precise definitions. Most of the
countermeasures suggest a broad range of treatments, thus limiting the execution of
quantitative analysis.
2: A reasonable number of sites with the same countermeasures implemented during the
analysis period are necessary for classifying them into control and treatment groups. The
ODOT data did not provide the possibility for grouping the available sites in this manner.
3: It was determined that any attempt to determine the effectiveness of countermeasures and
calculate crash reduction factors would only lead to misleading and inaccurate results. Hence,
the researchers requested ODOT to provide additional data that will be conducive to the
determination of crash reduction factors.
6.3 Request for Data
To summarize, the researchers worked on the following data that were previously received
from ODOT:
1. Crash data (1997- 2006) excluding work zone crashes
2. Countermeasures completed at different types of roadways (1999 - 2004).
Based on the data received from ODOT, the researchers had so far isolated the sites that were
applied with single treatments. Thereafter, the researchers categorized the sites into different
groups with sites that appeared to have been applied with similar countermeasures.
However, it should be noted that most of these countermeasures listed in ODOT data are
described in a broad manner without any specificity. It is necessary, therefore, to further
investigate these sites and countermeasures to determine if these data are suitable for
calculating crash reduction factors. The eighteen countermeasures listed in ODOT data are
shown in Table 8.
53
Table 8. Countermeasures Listed in ODOT Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Channelization and/or Turning Lanes
Access Management / Raised Median
Micro-surface to correct skid numbers or similar countermeasures
Resurface pavement or similar countermeasures
Lanes Added to Traveled Way
Sight Distance Improvements
Add speed limit signs or similar countermeasures
Signing improvements or similar countermeasures
Traffic Signal Installation or similar countermeasures
Improved signal coordination or similar countermeasures
Rumble strips on shoulders or similar countermeasures
Add lanes or similar countermeasures
Install 4-way stop and advance warning signage or similar
countermeasures
New interchange or similar countermeasures
Hill repaved for skid resistance or similar countermeasures
Widened Traveled Way or similar countermeasures
Reconstruct ramps should address issues or similar countermeasures
Add median should address issues or similar countermeasures
In order to further investigate the countermeasures and the sites where these countermeasures
were applied, the researchers generated the 18 tables (not included in this report) where each
table provided a list of sites where a countermeasure was applied. Each table contained the
following fields:
1. District
2. NLF_ID
3. County
4. Route
5. Begin Log
6. End Log
7. Countermeasure
8. Completion Date
Further investigation needed to be done to fully understand what specific countermeasure
was actually used at each site. For example, the countermeasure listed as “channelization
and/or turning lanes” did not fully explain what kind of channelization was used or if a left
turn lane, right turn lane or both right turn and left turn lanes were added. Without any
specific information, anything was open to assumption.
To facilitate further research, we requested ODOT to help us in getting in-depth data for each
countermeasure and roadway site as listed in the above-mentioned tables. Our data needs
were summarized in Tasks 1 thru 5 as shown below.
54
1. Task 1. For each site listed in each table, we requested ODOT to help us in
determining in further specific terms and details what countermeasure was exactly
used at each site. This information needs to be reviewed and finalized for all sites.
2. Task 2. Based on the outcome of Task 1, the researchers would prepare a revised list
of countermeasures and sites for further investigation.
3. Task 3. For the sites included in the revised list, the researchers would request ODOT
to provide the geometric features of each site before and after the countermeasures
were applied. The researchers would also request ODOT to provide the AADT data
for each site before and after the countermeasures were applied.
4. Task 4. Based on the information in Task 3, the researchers would further revise the
list of countermeasures and sites so that sites with similar geometric features and
AADT were grouped together for each countermeasure.
5. Task 5. Based on the information in Task 4, the researchers would request ODOT to
provide them with a list of other sites in the State of Ohio that have similar geometric
features, AADT and crash experience but where no countermeasures were applied
during the before and after periods. The purpose of this effort is to create comparison
groups for further analysis which will allow the researchers to perform the remaining
work and calculate crash reduction factors.
In the researchers’ opinion, the most important item was to begin with Task 1, which
required a detailed investigation of the countermeasure performed at each site. The
knowledge gained from completing Task 1 would allow them to work on Task 2, Task 3 etc
leading them toward the calculation of accident reduction factors.
55
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56
7.0: Conclusions
This study performed a review of the past literature on reduction strategies for rear end
crashes. The review has shown that research on crash reduction factors and accident
modification factors for rear end collision strategies is quite limited.
The ODOT data received by the researchers had severe limitations for analyzing the
effectiveness of countermeasures for rear end collision strategies. To facilitate further
research, the researchers requested ODOT to help them in getting in-depth data for each
countermeasure and roadway site. The data needs were summarized in a letter dated August
19, 2008 to ODOT. ODOT, however, decided not to proceed ahead with this research as it
required the dedication of district resources that were not currently available. ODOT
internally discussed the possibility of breaking the project into smaller, more manageable
pieces, but believed this approach would not yield results that would be statistically
significant. In addition, there were also several national projects underway which would limit
this project’s benefits.
In view of the above circumstances, ODOT decided to terminate the contract for this project
and all work stopped.
57
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58
8.0: Reference
1. National Transportation Statistics 2007, Bureau of Transportation Statistics, Research
and Innovative Technology Administration.
http://www.bts.gov/publications/national_transportation_statistics/2007/index.htm,
Accessed Dec. 28, 2008.
2. Facts, Statistics and Data. Federal Highway Administration, U.S. Department of
Transportation. http://safety.fhwa.dot.gov/facts/ , Accessed Nov. 28, 2007.
3. Status of NHTSA’s Rear-End Crash Prevention Research Program. National
Highway Traffic and Safety Administration, U.S. Department of Transportation.
http://www-nrd.nhtsa.dot.gov/pdf/nrd-01/esv/esv19/05-0282-O.pdf, Accessed Nov.
28, 2007
4. Crash Information. Department of Public Safety.
http://www.publicsafety.ohio.gov/crashes/crash_facts.asp, Accessed Dec. 28, 2008
5. Greg Murphy & Jennifer Townley. Strategies for Improving Strategies Safety and
Mobility on Ohio Roads.
http://www.otecohio.org/presentations/OTECpresentations/Se15/JT_GM-Safety.pdf,
Accessed June 28, 2007
6. Road way Safety and Mobility. Ohio Department of Transportation
http://www.dot.state.oh.us/planning/Safety/GoalsandObjectives.htm, Accessed Nov.
28, 2007
7. National Review of Highway Safety Improvement Program, US Department of
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2007
8. Estimates of Countermeasure Effectiveness Reduction (CRF) Factors. Road way
Safety and Mobility. Ohio Department of Transportation
http://www.dot.state.oh.us/roadwaysafety/PDF_Files/Crash%20Reduction%20Factor
s%20Table%202004.pdf. Accessed Nov 28. 2004
9. Estimates of Countermeasure Effectiveness Reduction (CRF) Factors. Office of
Systems Planning and Program Management, The Ohio Department of
Transportation.
http://www.dot.state.oh.us/planning/Safety/2006data/Crash%20Reduction%20Factors
%20FY2008.PDF, Accessed Nov. 28, 2007
10. Safety Study Guidelines. Office of Systems Planning and Program Management, The
Ohio Department of Transportation. Accessed Nov. 28, 2007
http://www.dot.state.oh.us/planning/Safety/PDF_Files/SafetyStudyGuidlines.pdf
11. Rate of Return Analysis. Office of Systems Planning and Program Management, The
Ohio Department of Transportation. Accessed Nov. 28, 2007
http://www.dot.state.oh.us/planning/Safety/SafetyPrograms.htm
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Driver Performance in Rear End Collisions. In Safety and Human Performance.
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Jan 9-13, 2000.
13. James G. Strathman, Kenneth J. Duecker, Jihong Zhang and Timothy Williams.
Analysis of Design Attributes and Crashes on the Oregon Highway System. Oregon
Department of Transportation, August 2001.
59
http://www.oregon.gov/ODOT/TD/TP_RES/docs/Reports/AnalysisDesignAtt.pdf.
Accessed Nov. 28, 2007.
14. Takashi Nakatsuji, Mansour Hadji Hosseinlou, Akira Kawamura, and Yuki Onodera.
Taking Tire Slip Ratio into Account and Estimating Friction Coefficients in Rear-End
Collisions on Winter Roads. In Maintenance. CD ROM Transportation Research
Record, Transportation Research Board, Washington, D.C. 2001 pp. 97 -103.
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Collision–Warning System Design and Evaluation via Simulation. In Safety and
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Transportation, 2002.
http://www.ncdot.org/doh/PRECONSTRUCT/traffic/Safety/ses/project_guide/region
alfactors110206.pdf. Accessed Nov.28, 2007
17. Joan Shen and Albert Gan. Development of Crash Reduction Factors: Methods,
Problems, and Research Needs. Transportation Research Board 2003 Annual Meeting
CD ROM, Washington D.C., Jan 12-16, 2003.
18. Mohamed A. Abdel-Aty and Hassan T. Abdelwahab. Configuration Analysis of TwoVehicle Rear-End Crashes, Transportation Research Board 2003 Annual Meeting CD
ROM, Washington D.C., Jan 12-16, 2003.
19. Santokh Singh. Driver Attributes and Rear-end Crash Involvement Propensity,
Research and Development, NHTSA, US Department of Transportation, March 2003.
http://www-nrd.nhtsa.dot.gov/pdf/nrd-30/NCSA/Rpts/2003/809-540.pdf, Accessed
June 22,2004
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Contributing Factors Using National Crash Databases. Research and Development,
NHTSA, US Department of Transportation, October 2004. http://wwwnrd.nhtsa.dot.gov/pdf/nrd-12/HS809664.pdf, Accessed Nov. 28, 2007.
21. Agent, Kenneth R Agent and Stamatiadis, Nikiforos. Development of Crash
Reduction Factors. Kentucky Transportation Center, University of Kentucky, June
1997. http://www.ktc.uky.edu/Reports/KTC_96_13.pdf. Accessed Nov. 28, 2007.
22. Vermont Strategic Highway Safety Plan, Vermont. Gov, December 2006.
http://www.atssa.com/galleries/default-file/VT_SHSP.pdf, Accessed March 28,2007
23. NCHRP Synthesis 310, Impact of Red Light Camera Enforcement on Crash
Experience A Synthesis of Highway Practice. Transportation Research Board. 2003.
http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_syn_310.pdf. Accessed Nov. 28,
2007
24. Strategic Highway Safety Plan, National Cooperative Highway Research Program.
2003. http://safety.transportation.org/guides.aspx. Accessed Nov 28,2007
25. Garber, Nicholas J., Miller, John S., Eslambolchi, Saeed, Khandelwal, Rahul,
Mattingly, Kimberly M., Sprinkle, Kristin M., Wachendorf, Patrick L. An Evaluation
of Red Light Camera (Photo-Red) Enforcement Programs in Virginia: A Report in
Response to a Request by Virginia’s Secretary Of Transportation. Virginia
Department of Transportation, University of Virginia, January 2005.
http://www.thenewspaper.com/rlc/docs/05-vdot.pdf, Accessed Nov. 28, 2007
60
26. Richards, C.M., Michaels, E.F., Campbell, J. Attitudes and Behaviors at Intersections
and Potential Effectiveness of Engineering Countermeasures Publication FHWAHRT-05-078. Office of Safety Research and Development, Federal Highway
Administration, November 2005. http://www.tfhrc.gov/safety/pubs/05078/05078.pdf.
Accessed Nov. 28, 2007.
27. Gan, Albert and Shen, Joan. Update of Florida Crash Reduction Factors and
Countermeasures to Improve the Development of District Safety improvement
Projects Lehman Center of Transportation Research, Department of Civil and
environmental Engineering, Florida International University. April 2005.
http://lctr.eng.fiu.edu/Documents/CRFFinalReport.pdf. Accessed Nov. 28,2007
28. Research Results Digest 299, National Cooperative Highway Research Program,
November 2005. http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rrd_299.pdf,
Accessed Nov. 28, 2007
29. Monsere,, Christopher M., Bertini,, Robert L., Breakstone,Aaron, Bonner,Carolyn,
Bosa, Peter,de la Houssaye, David, Horowitz, Zachary, and Hunter-Zaworski, Kate.
Update and Enhancement of ODOT's Crash Reduction Factors, Oregon Department
of Transportation. June 2006.
http://www.oregon.gov/ODOT/TD/TP_RES/docs/Reports/Crash_Reduction_Factors.
pdf, Accessed Nov. 28, 2007
30. Guidelines to Counter Measure Effectiveness & Crash Reduction Factor Illinois
Comprehensive Highway Safety Plan, Illinois Department of Transportation.
November 2006. http://www.dot.state.il.us/safetyEng/Appendix%20E.pdf, Accessed
Nov. 28,2007
31. Wiles, Poonam B., Cooner, Scott A., Walters, Carol H. and Pultorak and Edward J.
Advance Warning Of Stopped Traffic On Freeways: Current Practices And Field
Studies Of Queue Propagation Speeds. Publication FHWA/TX -03/4413-1. Texas
Department of Transportation, June 2003.
32. Wiles, Poonam B., Cooner, Scott A., Rathod, Yatin and Wallace Diane G. Advance
Warning Of Stopped Traffic on Freeways: Field Studies of Congestion Warning
Signs. Publication FHWA/TX -05/0-4413-2. Texas Department of Transportation,
March 2005
33. Pande, Anurag and Abdel_Aty Mohamed. A Comprehensive Analysis of the
Relationship between Real-Time Traffic Surveillance Data and Rear-End Crashes On
Freeways. TRB 06-0016, Manuscript prepared for the presentation at the TRB annual
meeting. November 2005. http://www.mdt.mt.gov/research/docs/trb_cd/Files/060016.pdf .Accessed March 23, 2004
34. Davis, Gary A. Swenson, Tait. Identification and Simulation of a Common Freeway
Accident Mechanism: Collective Responsibility in Freeway Rear-end Collisions.
Department of Civil Engineering, University of Minnesota, April 2006.
http://www.cts.umn.edu/pdf/CTS-06-02.pdf. Accessed Nov. 28,2007
35. Kim, Joon-Ki, Wang Yinhai and Ulfarsson, Gudmundur F. Modeling The Probability
Of Freeway Rear-End Crash Occurrence. Paper Submitted to Journal of
Transportation Engineering. June 2006.
http://www.uwstarlab.org/STARLab_Papers/2006_JTE_FRE.pdf, Accessed Nov. 28,
2007
61
36. Hovey, Peter W.and Chowdhury, Mashrur. Development of Crash Reduction Factors.
Safety Research Document, Ohio Department of Transportation September 2005.
http://www.dot.state.oh.us/research/2005/Safety/14801-FR.pdf. Accessed Nov.28,
2007.
37. Pant, P.D., Liu Y. and Vasisht G. Rational Schedule of Base Accident Rates for Rural
Highways in Ohio (Phase-I). Publication FHWA/OH -2000/003. Ohio Department of
Transportation, January 2000.
38. Pant P.D., Rajagopal, A. and Cheng, Y. Rational Schedule of Base Accident Rates for
Rural Highways in Ohio (Phase-II). Publication FHWA/OH - 2003/008. Ohio
Department of Transportation, June 2003.
39. Pant P.D. and Kashayi, Nagaraju. Draft Final Report Crash Base Rates For
Intersections In Ohio. Research performed for the Ohio Department of Transportation
by University of Cincinnati, Ohio. December 2006
40. Pant P.D. and Panta, Subarna. Draft Final Report Crash Base Rates For Freeways In
Ohio. Research performed for the Ohio Department of Transportation by PDP
Associates Inc., Ohio. March 2007.\
41. Accident Modification Factors for Traffic Engineering and ITS Improvements,
NCHRP report 617, National Cooperative Highway Research Program, 2008.
http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_617.pdf, Accessed Dec. 28,
2008.
42. Joan Shen and Albert Gan. Development of Crash Reduction Factors: Methods,
Problems, and Research Needs. Transportation Research Board 2003 Annual Meeting
CD ROM, Washington D.C., Jan 12-16, 2003.
43. F.M Council, D.W. Reinfurt, B.J. Campbell, F.L.Roediger, L.Carroll, A.K.Dutta, &
J.R.Dunham. Accident Research Manual, Publication FHWA/RD-80/016, Federal
Highway Administration, US Department of Transportation, 1980
44. Expert System for Highway Safety Analysis Advising. Prepared by University of
Cincinnati for Ohio Department of Transportation, February 12, 1996.
62
Appendix I
Simple Before and After Comparison
63
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64
Table 1.1: Simple Before and After Comparison for Countermeasures employed in
Intersections from year 2001 – 2004.
Intersection
2001
Dist
NLF_ID
SHURSR00061**C
Begin
Log
2.6
End
Log
2.7
3
4
SPORSR00014**C
9.75
11.8
4
SSUMSR00241**C
4.55
4.65
7
8
SCLASR00041**C
SCLEUS00050**C
31
1.54
31.1
1.64
Countermeasure
Before
After
Percent
Channelization and/or Turning
Lanes
At SR44/Chestnut
intersection, upgraded signal
to box span; striped
SR44/Chestnut with LT
storage and added LT phases
on all approaches. Completed
FA 12/19/01
2
3
-50.00
26
54
-107.69
Channelization and/or Turning
Lanes
New Traffic Signal/Flashers
Lanes Added to Traveled Way
2
9
-350.00
0
8
1
22
-100.00
-175.00
Countermeasure
Before
After
Percent
Add lanes completed-monitor
results
Mill to improve skid resistance
duplicate location see above
Epoxy pavement markings,
completed 10/15/02; PID
#24177
18
3
83.33
402
175
56.47
65
25
61.54
Improve Exit Ramp at CleveMass
60
17
71.67
Countermeasure
Before
After
Percent
Left turn phase added
Rehabilitate Roadway
Reconstruct intersection,
installing LT lanes on SR164
and SB RT lane on SR 7 and
increasing approach radii;
Signal upgrade addition of
turn phases.
107
112
3
172
161
5
-60.75
-43.75
-66.67
2002
Dist
NLF_ID
SCUYIR00090**C
Begin
Log
3.56
End
Log
3.82
12
12
SCUYIR00090**C
16.2
18.2
4
SSUMIR00077**C
0
3.8
4
SSUMIR00077**C
20
21.5
2003
Dist
NLF_ID
12
10
4
SLAKSR00091**C
SATHUS00033**C
SMAHSR00007**C
Begin
Log
2
2.77
3.45
End
Log
4
4.81
3.45
65
12
SLAKSR00306**C
5.55
6.91
New interchange at SR 615
and-90 will help by reducing
traffic on SR 306 - monitor
229
300
-31.00
4
STRUSR00007**C
8.6
8.6
At SR82 intersection,
construct offset LT lanes on
SR82, LT lanes on SR7 and
RT lane on SR7 SB approach.
2
5
-150.00
7
SMIASR00055**C
9.79
11.8
HS - City of Troy Widening
and Increasing Intersection
Radius between SLM 10.50
and 11.15; Replacing 2
Traffic Signals; work to be
Completed Spring ‘03, monitor
crash frequency.
106
138
-30.19
7
SMIAUS00036**C
10.8
11.1
LS - Removal of parking on
street
21
27
-28.57
2004
Dist
NLF_ID
End
Log
20
Countermeasure
Before
After
Percent
SMEDSR00018**C
Begin
Log
18
3
This section is in a rural area
with a high number of Animal
accidents. Upgrade signing to
meet conditions.
26
36
-38.46
4
SMAHSR00007**C
8
12.1
139
112
19.42
7
SMOTSR00725**C
14.3
16.3
273
280
-2.56
8
SWARSR00048**C
23.1
23.1
Improve sign location and size
through section after
evaluation
2003 - Micro surface to
improve skid resistance
Widn4AprForLTLS/UpgrdSgns
1
0
100.00
12
SLAKSR00306**C
5.18
5.53
New interchange at I-90 and
SR 615 should alleviate
congestion along the SR 306
corridor
35
30
14.29
66
Table 1.2: Simple Before and After Comparison for Countermeasures employed in
Interstate from year 2001 – 2004.
Interstate
2001
Dist
NLF_ID
SSUMIR00076**C
Begin
Log
5.9
End
Log
6.59
4
7
SCLAIR00070**C
2.47
3.97
12
SCUYIR00071**C
5.37
5.85
Countermeasure
Before
After
Percent
Upgrade extrusheet signs,
supports, lighting; PID
#17965
Remove concrete curb/
fixed deficient radius ramp
E
Straighten loop ramps.
Remove right turn slip
ramps and T the exit ramp
into US 42. This work was
completed on the
southbound exit ramp as
part of CUY-71-0.00
project.
32
34
-6.25
10
14
-40.00
104
82
21.15
2002
Dist
NLF_ID
Begin
Log
End
Log
Countermeasure
Before
After
Percent
12
SCUYIR00090**C
3.56
3.82
18
3
600.00
12
SCUYIR00090**C
16.2
18.2
Add lanes completedmonitor results
Mill to improve skid
resistance duplicate
location see above
402
175
229.71
4
SSUMIR00077**C
0
3.8
Epoxy pavement
markings, completed
10/15/02; PID #24177
65
25
260.00
4
SSUMIR00077**C
20
21.5
Improve Exit Ramp at
Cleve-Mass
60
17
352.94
Countermeasure
before
after
percent
Enhance warning signs for
SB exit loop ramp
Interchange
improvements
5
17
-240.00
186
34
81.72
2003
Dist
NLF_ID
SHANIR00075**C
Begin
Log
15.1
End
Log
15.6
1
3
SLORIR00090**C
15.3
15.9
67
4
SSTAIR00077**C
14
18
Include Portable Message
Board in construction
plans to alert traffic to
slower moving traffic
ahead
Install YIELD sign for WB
ramp from US 422
Install 2 merge warning
signs, relocate 3, install 1
Yield sign (LS)
265
436
-64.53
4
STRUIR00080**C
1.57
3.14
20
16
20.00
6
SFRAIR00070**C
16
18
158
267
-68.99
6
SFRAIR00270**C
28
30
Install Watch For Stopped
Traffic signs EB 270, east
of SR 3 (LS) EVAL
107
130
-21.50
6
SFRAIR00670**C
3
5
133
342
-157.14
SCLAIR00070**C
5.51
6.07
8
5
37.50
7
SMIAIR00075**C
5.08
5.52
4
2
50.00
7
SMIAIR00075**C
6
8
89
31
65.17
7
SMIAIR00075**C
7.33
9.35
Section currently under
total reconstruction (HS)
HS - Add Lane Project
PID 17448, From 5.14 to
6.83
HS - Design Build Project
PID 11160, SLM 4.94 to
SLM 10.84 Add Lane,
Roadway work
substantially complete,
Open to Traffic.
HS - Add Lane project to
increase interstate
capacity.
Design build project to
add lane on I75, SLM 4.94
to SLM 10.84.
7
91
31
65.93
11
12
SBELIR00070**C
SCUYIR00090**C
20
12
20
14
14
170
13
211
7.14
-24.12
12
SCUYIR00090**C
18
20
110
208
-89.09
12
SLAKIR00090**C
6.6
7.67
Revise Traffic Signal
Milled to improve skid
resistance
Improve signing and
pavement markings
Capacity addition
completed in 9/15/03 (4 to
6 lanes) west of SR 306
42
36
14.29
Countermeasure
Before
After
Percent
widen to six lanes
Extend channel line for I76 EB to I-77 SB ramp
2003 Added Thru-75Arrow
03 - Micro-surface to
correct skid numbers.
2
168
0
173
100.00
-2.98
824
737
10.56
72
81
-12.50
2004
Dist
NLF_ID
SLUCIR00280**C
SSUMIR00076**C
Begin
Log
4.91
10
End
Log
5.1
12
2
4
7
SMOTIR00075**C
3.74
20.4
7
SMOTIR00075**C
10
12
68
8
SBUTIR00075**C
0
6.72
Major widening PID 10751
and study PID 75971
should address issues
453
352
22.30
8
SHAMIR00071**C
7.53
8.03
21
23
-9.52
8
8
SHAMIR00071**C
SHAMIR00071**C
9.82
12
10.1
14
15
93
12
119
20.00
-27.96
8
SHAMIR00071**C
14
16
186
183
1.61
8
SHAMIR00071**C
16
18
180
97
46.11
8
SHAMIR00071**C
18
19.9
187
141
24.60
8
SHAMIR00074**C
5.73
6.26
2
2
0.00
8
SHAMIR00074**C
9.2
9.33
2
3
-50.00
8
SHAMIR00074**C
16
18
56
73
-30.36
8
SHAMIR00074**C
17.4
17.7
10
10
0.00
8
SHAMIR00074**C
18
18.8
34
33
2.94
8
SHAMIR00074**C
18.5
19
abb, Add signs on Ramps
and exit panels
Add speed limit signs
Rumble strips on
shoulders.
Rumble strips on
shoulders.
Rumble strips on
shoulders.
Rumble strips on
shoulders.
Signs/Turnarounds, Signs
up 7/13/99
PID 75730 to reconstruct
ramps should address
issues
Rumble strips on new
pavement
PID 78082 ramp meters
should address issues
PID 78082 to add ramp
meters should address
issues
continue with projects to
redesign interchange and
install ramp metering
52
44
15.38
8
SHAMIR00074**C
19.2
19.5
18
10
44.44
8
SHAMIR00275**C
18.6
20.6
63
86
-36.51
8
SHAMIR00275**C
23.4
29.8
499
375
24.85
8
SHAMIR00275**C
24
24.6
60
69
-15.00
8
SHAMIR00275**C
30.7
31.6
PID 76257 to reconstruct
interchange and PID
78082 to install ramp
meters should address
issues
Remove unpaved
crossovers.
PID 77000 to reconstruct
ramps should address
issues
widening project PID
22386 should address
safety issues
PID 20128 to add aux
lane from 42 to RHH
should address issues
54
29
46.30
8
SWARIR00075**C
10
12.2
PID 10754 widening to the
MOT Co line should
address issues
22
20
9.09
12
SCUYIR00090**C
14.5
14.9
Install rumble strips
36
34
5.56
69
This page is intentionally left blank
70
Table 1.3: Simple Before and After Comparison for Countermeasures employed in
Non-Interstate from year 2001 – 2004.
Non-Interstate
1999
Dist
NLF_ID
4
SPORSR00059**C
Begin
Log
5.81
End
Log
7.81
Countermeasure
Before
After
Percent
Widen to 4 lanes from
Menough to Ravenna
West Corp Limit
111
83
25.23
Countermeasure
Before
After
Percent
New Traffic
Signal/Flashers
Widen to four std width
lanes with necessary
left turn lanes where
needed from State Rd
to SR 11
Traffic Signs, Pavement
Markings and/or
Delineators
Minor Structures
Replaced or Improved
for Safety
Lanes Added to
Traveled Way
Lanes Added to
Traveled Way
Channelization and/or
Turning Lanes
Channelization and/or
Turning Lanes
Roadway Realignment
Traffic Signs
12
6
50.00
77
94
-22.08
98
94
4.08
7
5
28.57
200
124
38.00
17
105
-517.65
77
49
36.36
13
7
46.15
183
15
141
9
22.95
40.00
Countermeasure
Before
After
Percent
Sight Distance
Improvements
1
1
0.00
2000
Dist
NLF_ID
SHANSR00037**C
Begin
Log
2.7
End
Log
3.23
1
4
SATBUS00020**C
13.5
14.5
4
SMAHSR00046**C
13.9
14.7
4
SPORSR00303**C
6.83
8.02
7
SMOTSR00741**C
4.28
7.37
8
SBUTSR00747**C
1.71
3.16
8
SCLESR00125**C
7.02
8.63
8
SCLESR00125**C
7.02
8.63
8
9
SCLEUS00052**C
SLAWSR00007**C
5.32
5.04
6.1
5.14
2001
Dist
NLF_ID
1
SDEFSR00066**C
Begin
Log
0.97
End
Log
2.06
71
4
SATBSR00045**C
19.3
19.9
4
SATBUS00020**C
12.8
13.3
4
SMAHSR00046**C
14.7
14.7
4
SMAHSR00046**C
14.7
14.9
4
SPORSR00014**C
9.01
10.3
4
SPORSR00043**C
8
10
4
SPORSR00043**C
13.5
14
4
SSTASR00687**C
2.46
2.46
4
SSUMSR00241**C
4.09
4.49
4
STRUSR00087**C
0
2.51
5
SFAISR00037**C
11.4
11.5
5
SFAISR00188**C
4.46
4.56
ATB-45-19.74, PID
#18703, Completed
Aug.01: Added SR45
center turn lane storage
and LT storage on I-90
exit ramps
ATB-20-20.921(M), PID
#8254, Completed July
01: Widen viaduct to
four std width lanes with
necessary left turn lanes
where needed from
Park Ave to State Rd.
Extended SR46 turn
lane storage lengths;
Signal upgrade; MAH46-14.52, PID #14974
Project completed 5-3101
Channelization and/or
Turning Lanes
S.R.44/Chestnut restriped to add LT lanes
on existg pavt. Signal
upgraded to box span
and LT phases added.
Resurfaced SLM 8.3015.51, PID 17880
Guardrail end
treatments upgraded
with project POR-438.300, #17880
STA-687-1.94, PID
#6256 Completed
10/31/01. Widened SR687 through
intersection. Everhard
widened by county
1998, STA-CR98-2.29,
PID #4276.
S.R. 241 @ S.R. 619
intersection widened for
turn lanes, added
intersection lightg and
sig. upgrade
Lanes Added to
Traveled Way
Channelization and/or
Turning Lanes
Sight Distance
Improvements
14
24
-71.43
29
51
-75.86
27
33
-22.22
15
6
60.00
22
22
0.00
105
102
2.86
10
4
60.00
12
16
-33.33
12
26
-116.67
17
5
70.59
6
5
16.67
1
5
-400.00
72
5
SKNOUS00036**C
18.2
19.1
5
SLICSR00161**C
2.14
2.24
7
SMOTSR00202**C
5.17
5.27
8
SCLEUS00050**C
4.72
5.84
8
8
SCLEUS00050**C
SHAMSR00264**C
7.66
6.85
8.26
6.95
10
SNOBSR00078**C
5.49
6.89
11
STUSUS00250**C
19.2
21.7
12
SLAKSR00608**C
0.3
0.96
12
SLAKSR00608**C
0.5
1
Make Division St. lef a
one-way which would
eliminate the left turn
from US 36. District will
meet with the city to
discuss this suggestion.
Channelization and/or
Turning Lanes
Lanes Added to
Traveled Way
Widen to 12ft lane and
4ft shoulders
Repaved
Channelization and/or
Turning Lanes
Widened Traveled Way
(No Lanes Added)
2. a. A construction
project at the
intersection of
McCauley Drive was
completed in October
2001. The project
added turn lanes, new
concrete pavement,
new signals, new signal
ahead signs w/flashers,
and new pavement
markings.
Hill repaved for skid
resistance
Hill repaved for skid
resistance
16
79
-393.75
13
16
-23.08
8
11
-37.50
27
12
55.56
2
15
1
33
50.00
-120.00
1
1
0.00
55
35
36.36
3
0
100.00
3
0
100.00
Countermeasure
Before
After
Percent
MAJOR
REHABILITATION OF
BRIDGE OVER IR 90.
ADD A 2WLTL,
INCLUDING A
CURBED TYPICAL
SECTION WITH A
CLOSED DRAINAGE
SY STEM.
CONSTRUCT
SIGNALIZED
INTERSECTION.
Added Turn Lanes on
Harper Road Exit Ramp
in 2002 to relieve
queuing onto Freeway -
21
6
71.43
16
5
68.75
91
28
69.23
2002
Dist
NLF_ID
SATBSR00534**C
Begin
Log
19.3
End
Log
20.4
4
11
SCOLSR00045**C
15.1
15.8
12
SCUYUS00422**C
15.2
17.2
73
monitor -skid test
pavement
3
9
SERIUS00250**C
SJACSR00093**C
9.75
7
10.4
9
9
SJACSR00093**C
14.9
15.4
9
SJACSR00093**C
15
15.4
9
SJACSR00093**C
15
15.4
12
SLAKSR00640**C
1.76
2.14
2
SLUCUS00020**C
18.9
19.2
4
SMAHSR00045**C
11.8
11.8
7
SMOTUS00040**C
3.13
3.13
4
SSUMSR00018**C
2.12
2.58
4
SSUMSR00018**C
8
10
4
SSUMSR00091**C
17.2
18.2
Widen to 5-lanes
Install large Arrow sign
with flashers, Overlay
pavement
Monitor, Pavement was
widened in June 2002 to
provide a center two
way left turn lane
9
2
0
0
100.00
100.00
25
6
76.00
WIDEN A SECTION OF
SR93 AND ADD A CEN
TER TWO-WAY LEFTTURN LANE FOR
SAFETY.
Widen pavement for two
way left turn lane
Widening project
completed
build new four lane
bridge
Warning sign relocation
on county route
approaches and signal
timing/phasing
operational evaluation.
Upgraded Stop Signs
and added Stop Lines.
Recent projects added
cap. via addtl lanes &
signal cood. (PID #7861
& #20697). Requires
correction of I value = 6,
slm 2.10-3.16 and
recalc. HSP rank. Refer
to SCWP.
Widen to standard lane
width with turn lanes
where needed;
drainage, curbs,
sidewalks, lighting;
access management,
signal
upgrade/coordination,
drainage improvements;
create off street parking
S.R. 91 widened to 5
lanes north of Old Mill,
installed signal at Old
Mill
22
6
72.73
22
6
72.73
25
4
84.00
21
2
90.48
4
1
75.00
1
0
100.00
72
27
62.50
108
43
60.19
25
10
60.00
74
4
SSUMSR00093**C
6.92
7.71
10
SVINUS00050**C
11.4
13.6
10
SVINUS00050**C
11.9
14
8
SWARSR00123**C
16.5
16.9
2
SWOOSR00065**C
5.91
6.62
Resurfaced 9/30/02;
PID#17949 (included
striping change NB at
Cormany)
Widen US 50 and
perform minor horizontal
and vertical
realignments.
ROAD REALIGNMENT,
WIDENING AND
PAVING SHOULDERS,
DRAINAGE, GRADING,
AND RESURFACING
WITH GUARDRAIL
INSTALLATION
sign improvements
28
23
17.86
3
1
66.67
3
0
100.00
1
0
100.00
3
0
100.00
Countermeasure
before
after
percent
Remove School
Crossing sign in front of
Thomas More
TRAC funded widening
project completed
build new four lane
bridge
Install Closed Loop
System
Install O.H. flasher at
Alabama Ave
intersection. Sign
upgrade & visibility
improvements via
foliage removal. Create
left turn lane on SR 172
on existing pavement no widnening
Resurface with skid
resistant material - PID
19850 FY 2003
387
669
-72.87
99
66
33.33
10
15
-50.00
49
74
-51.02
3
0
100.00
6
4
33.33
REALIGN TO PROVIDE
PROPER
SUPERELEVATION
BY CHANGING HORIZ.
& VERTICAL CURVES;
RELOCATE TR-22 &
SR-65 INTERSECTION
FOR PROPER SIGHT
DISTANCE; PERFORM
RELATED WORK.
2003
Dist
NLF_ID
SCLESR00125**C
Begin
Log
0
End
Log
2
8
12
SCUYSR00091**C
0
2.45
2
SWOOUS00020**C
0
0.46
4
STRUSR00193**C
0.2
1.48
4
SSTASR00172**C
0.9
0.9
4
STRUSR00046**C
1.7
2.6
75
8
SHAMSR00125**C
1.76
2.5
8
10
SCLESR00126**C
SWASSR00060**C
1.78
1.82
1.78
2.83
8
SCLESR00125**C
2
4
12
SLAKSR00002**C
2
4
7
SMIASR00202**C
2.03
2.03
10
SATHUS00033**C
3.29
3.88
8
SCLESR00125**C
3.31
3.31
8
SCLESR00125**C
3.44
3.44
4
STRUSR00046**C
3.72
5.52
12
SCUYSR00017**C
3.76
4.39
12
SCUYUS00020**C
3.99
3.99
12
SLAKSR00002**C
4
6
12
SLAKSR00306**C
4
4.74
7
SMOTSR00048**C
4
6
4
SATBUS00020**C
4.66
4.66
City creating 5 lane
section, under
construction.
Trim Trees, add signs
Permit Review to
Ensure Compliance
McMann-Gordon
intersection improved
2002
IR90 and SR615 new
interchange
construction to be
completed fall FY2003
will help SR 2 corridor
Re-alignment/ Traffic
Signal
Rehabilitate Roadway,
including Access
Management
(CONT: CLOSE
DRIVES/RELOCATE
DR
TurnLns/ReloMcMan&G
ordon/UpgrdSgnl
Upgrade and
interconnnect signals
via PID 22204, FY03
Realignment at Grayton
Road completed monitor results
New signal installed
November of
2003/recommend
monitoring and waiting
for 2004 and 2005
accident data to
reevaluate effectiveness
of improvements
IR90 and SR615 new
interchange
construction to be
completed fall FY2003
will help SR 2 corridor
New interchange at SR
615 and-90 will help by
reducing traffic on SR
306 - monitor
MM - Close (or RightIn/Right-Out) Access
Points,Access
Management
ATB-20-4.67, PID
#24093, FY03 CO:
Install 4-phase, fullyactuated signal at
73
79
-8.22
2
42
0
71
100.00
-69.05
100
143
-43.00
83
127
-53.01
6
5
16.67
33
50
-51.52
2
1
50.00
9
10
-11.11
90
70
22.22
2
20
-900.00
3
5
-66.67
142
153
-7.75
17
30
-76.47
123
151
-22.76
3
1
66.67
76
Meyers Road
intersection
3
SMEDSR00303**C
4.98
4.98
Signing improvements
3
4
-33.33
11
8
STUSSR00800**C
SHAMSR00125**C
5.17
5.39
5.79
7.39
1
182
1
474
0.00
-160.44
12
SLAKSR00002**C
6
8
86
110
-27.91
12
SGEASR00088**C
6.11
6.11
Add curve signing
County improving
Asbury, add lanes on
Asbury, drive
improvements on 125
IR90 and SR615 new
interchange
construction to be
completed fall FY2003
will help SR 2 corridor
Signalization
0
2
#DIV/0!
12
SLAKSR00306**C
6.15
6.91
186
252
-35.48
4
STRUSR00005**C
6.6
7.19
3
1
66.67
8
12
SBUTSR00747**C
SLAKSR00306**C
7.03
7.08
7.03
7.84
6
53
6
62
0.00
-16.98
5
SFAIUS00033**C
8
10
0
6
#DIV/0!
8
SHAMSR00264**C
8
10
274
431
-57.30
7
SMOTSR00202**C
8.57
8.87
56
68
-21.43
8
SHAMSR00264**C
8.64
8.64
15
12
20.00
7
SMIAUS00036**C
8.83
10.1
31
50
-61.29
3
SLORSR00082**C
9.05
9.05
10
1
90.00
New interchange at I-90
and SR 615 should
alleviate congestion
along the SR 306
corridor
Skid resistant paving of
W. Market interchange
CutHill,Radii,LTLs
New interchange at SR
615 and-90 will help by
reducing traffic on SR
306 - monitor
Coonpath Rd. signal is
being rebuilt and
upgraded as part of the
bypass construction.
Left turn lanes are being
constructed on all
approaches.
Adding protected lt.
phase at Westbourne
this year.
LS - Restrict turning
movements, Review
Signal Timing and
Coordination.
Improved signal
coordination,Westbourn
e/Law.
HS - City has widened
roadway and installed a
new traffic signal at US
36 and College St.
Upgrade crossroad
warning signs
77
7
SMOTSR00202**C
9.1
9.62
LS - Restrict turning
movements, Review
access management.
12
14
-16.67
9
SSCIUS00023**C
9.36
11.4
42
38
9.52
4
STRUSR00045**C
9.41
11.4
71
80
-12.68
5
SLICSR00013**C
9.88
10.1
39
33
15.38
5
SFAIUS00033**C
10
12
1
4
-300.00
4
SSUMSR00261**C
11.6
12
76
67
11.84
12
SCUYSR00087**C
11.8
13.8
Install Watch For
Stopped Traffic signs
and Thru Traffic Keep
Right signs / Request
Increased enforcement
of speed limit,
Signal head blocking
NB O.H. advance
signing for 5/82 WB Entr
ramp. Improve location
of sign - advance
ground mount
City of Newark
completed signal
upgrades Jan 03.
ODOT will work with the
city to monitor, optimize,
and coordinate signal
timing.
As a low cost, short
term countermeasure,
ODOT will better
interconnect the signals
at Collins Rd. and Victor
Dr.
Adjust signal timing letter to city
Restripe narrow 4 lanes
to 3 lanes with center
two way left turn lane
89
131
-47.19
8
SHAMUS00022**C
12.5
12.5
32
35
-9.38
4
SMAHSR00046**C
12.8
14.8
122
122
0.00
:LO)
SCUYSR00014**C
13.1
13.1
1
12
-1100.00
9
SROSSR00104**C
14.2
14.4
21
19
9.52
4
SSUMSR00008**C
16
18
171
320
-87.13
8
SHAMUS00022**C
18
19.3
100
173
-73.00
Remove signs /
vegetation
Perform semi-annual
striping
New signal installed
May of
2003/recommend
monitoring and waiting
for 2004 and 2005
accident data to
reevaluate effectiveness
of improvements
Widen off ramp to add
right turn lane, move
signal pole for widening
Install advance street
name signs
Developer adding
TWLTL between Union
Cemetery and Enyart.
78
9
SROSUS00035**C
20.1
20.5
8
SCLIUS00068**C
20.4
20.8
10
SWASSR00007**C
21.5
21.9
10
SWASSR00007**C
22.8
22.8
Revise signal timing,
Install Through Traffic
Keep Left signs
Work to be done by
developer, add turn
lanes at intersection
Coordinate and
Optimize Signals
Optimize Signal Timing
4
SSTAUS00062**C
24
28
Install / replace RPMs
8
2
75.00
6
8
-33.33
25
20
20.00
13
20
-53.85
283
470
-66.08
Countermeasure
Before
After
Percent
Modify signal clearance
(y & all red) times.
review time-lapse video
to identify current traffic
patterns
Install flashers on night
arrow sign
Install edgeline rumble
strips from slm 3.48 to
8.0 (Rumble strips
already installed from
slm 8.0 to slm 11.14 (I90).)
Optimize traffic signal
operation at SR 57 and
IR 90.
Optimize traffic signal
operation at SR 57 and
SR 254.
4
9
-125.00
19
20
-5.26
3
1
66.67
23
12
47.83
234
209
10.68
90
95
-5.56
26
36
-38.46
9
3
66.67
97
58
40.21
10
5
50.00
2004
Dist
NLF_ID
SALLSR00309**C
Begin
Log
10.9
End
Log
10.9
1
2
SLUCSR00025**C
8.2
8.47
3
SERIUS00006**C
0.88
1.41
3
SLORSR00002**C
7.97
9.97
3
SLORSR00057**C
18.2
20.2
3
SLORSR00057**C
20.2
22.2
3
SMEDSR00018**C
18
20
3
SMEDSR00083**C
0.01
0.51
3
SMEDUS00042**C
18
20
3
SMEDUS00042**C
20.8
21.3
This section is in a rural
area with a high number
of Animal accidents.
Upgrade signing to
meet conditions.
Replace existing signal
ahead signs with
flourescent yellow signal
ahead signs.
Improve pavement
markings and lane use
signing.
Install 45mph speed
zone from end of exist.
35mph speed zone to
Sleepy Hollow Road.
79
3
SRICUS00042**C
12
14
3
SRICUS00042**C
14
16
4
SMAHSR00007**C
8
12.1
4
SMAHSR00626**C
0.4
0.9
4
SMAHUS00224**C
17.9
19.1
4
SPORSR00261**C
3.85
3.85
4
SSTASR00173**C
1.85
1.85
4
SSUMSR00091**C
9.59
9.59
4
STRUSR00046**C
10.5
10.5
4
STRUSR00082**C
16.8
18.8
4
STRUUS00422**C
9.92
11.4
6
SFRASR00317**C
5.18
5.18
6
SFRAUS00033**C
26
28
7
SMIASR00041**C
9.49
9.49
Evaluate signing and
pavement markings for
improvements.
Implement any indicated
changes.
Evaluate speed limits
for possible
adjustments.
Improve sign location
and size through section
after evaluation
Improve lane and
shoulder width and
degree of curvature
and/or superelevation of
the curve between slm
0.40 and slm 0.70.
Skid Resistant Overlay,
slm 18.22 - 20.72
_Add
protected_permissive
left turn phases to signal
operation. WB and SB
left turns heaviest
Intersection
realignment/relocation
to create standard 2way stop condition on
the Columbus (CR67)
approaches
Add second 5-unit
signal head for EB left
turn
Realign intersection of
McCleary-Jacoby with
SR 46, Add NB LT lane
on SR 46
Restripe EB ramp from
E. Market to one lane to
reduce number of lanes
merging onto SR 82 Not Performed: See
Comments
Upgrade and
interconnect signals
along section. Included
in citywide closed loop
project. PID 22694
FY03
add left and right turn
lanes at Rohr Road
intersection
remove traffic signal
(LS) EBRIGHT
LS - Re Design Traffic
72
53
26.39
40
33
17.50
139
112
19.42
2
0
100.00
234
179
23.50
4
7
-75.00
2
0
100.00
18
13
27.78
1
0
100.00
121
39
67.77
33
23
30.30
1
1
0.00
42
22
47.62
3
2
33.33
80
7
SMOTSR00201**C
7.37
9.37
7
SMOTSR00725**C
12.3
14.3
7
SMOTSR00725**C
14.3
16.3
7
SMOTSR00741**C
2.93
2.93
7
SSHESR00047**C
14
15.5
8
SBUTSR00004**C
0.44
4.89
8
SBUTSR00004**C
12
14
8
SBUTSR00004**C
23.3
24.3
8
SBUTSR00747**C
0
2
8
SBUTSR00747**C
1.01
1.01
8
SCLESR00028**C
6.83
8.83
8
SCLESR00032**C
0
2
8
SCLESR00032**C
8
10
8
SCLESR00125**C
6
8
8
8
SCLESR00131**C
SGREUS00035**C
2
2.55
4
4.55
8
SHAMSR00125**C
3.39
5.39
8
SHAMSR00562**C
0.56
1.06
8
SHAMUS00027**C
11.4
14.3
Pattern
2003 Major Rehab on
SR 201 N of I70
2003 - Micro-surfaced to
improve skid numbers
2003 - Micro surface to
improve skid resistance
LS-Review and improve
pavement markings,
repair twisted sign, add
LT Lane sign.
2003 Roadway
improvements to SR 47
and 4th Ave
PID 76380 to add nb
and sb lanes should
address issues
Upgrade Stop when
flashing sign at SR747.
ADD 2 ThruLNS
TRENTN/FRNKLNBRDG
Left turn on arrow only,
if left turns are a
problem at Mulhauser
continue with
countermeasure to
install protected left
Adding left turn lane at
Goshen with resurfacing
Remove median
crossing at Roney Lane,
eliminate lefts
Fix prepare to stop
when flashing, use
correct size symbolic
sign.
Left turn lanes at newly
relocated Cecilia in
Amelia, by village
Improve alignment
Interchange being
constructed at North
Fairfield Road
Change Salem from
Protected left to
protected/permissive
The placement of the
flasher west of this
section should address
safety issues
PID 76378 to add
median should address
57
113
-98.25
81
41
49.38
273
280
-2.56
18
18
0.00
85
65
23.53
366
319
12.84
37
48
-29.73
10
8
20.00
83
68
18.07
10
5
50.00
34
27
20.59
115
56
51.30
57
70
-22.81
78
75
3.85
72
117
46
61
36.11
47.86
57
70
-22.81
24
18
25.00
387
414
-6.98
81
issues
8
SHAMUS00027**C
11.7
13.7
8
SHAMUS00027**C
13.1
14.4
8
SHAMUS00027**C
14.3
14.3
8
SHAMUS00027**C
14.7
14.7
8
SHAMUS00127**C
11.9
13.9
8
SHAMUS00127**C
12.8
8
SWARSR00048**C
8
Under construction for
center median.
Access Management /
Raised Median
Access Management /
Raised Median
Add right turn lane NB
271
289
-6.64
180
202
-12.22
1
1
0.00
16
10
37.50
Spingdale intesection
12.75 on HSP being
studied, add LT. phase.
32
60
-87.50
12.8
Retime signal
5
11
-120.00
23.1
23.1
1
0
100.00
SWARSR00122**C
2.77
3.42
10
6
40.00
8
SWARSR00132**C
2.58
2.58
1
0
100.00
8
SWARUS00022**C
5.37
5.37
7
12
-71.43
9
SBROSR00032**C
11.1
11.1
Widn4AprForLTLS/Upgr
dSgns
Widen to 12ft lane and
8shoulders
Improve sight dist., cut
hill to south
RECNST
INTRSCT/SIGNL TO 8
PHS/LTLS
Install stop & go signal
0
1
-100.00
9
SJACSR00093**C
14
16
68
56
17.65
9
SLAWSR00093**C
3.88
4.66
7
12
-71.43
10
SWASUS00050**C
9.73
10.5
9
8
11.11
12
SLAKSR00044**C
0
2.07
57
51
10.53
Resurface pavement,
Install new RPMs and
thermoplastic pavement
markings/14.40-15.33
scheduled for widening
Nov. 2008 (See HSP
locations)
The DSRT recommends
to remove unwarranted
guardrail posts and
monitor accidents, The
speed limit was reduced
to 45 mph in 2002
Improve Signing and
Striping
Perform skid test and
modify pavement as
necessary. Emergency
contract sold (project
9075-04) and work
completed.
82
12
SLAKSR00044**C
1.69
2.3
12
SLAKSR00306**C
5.18
5.53
Perform skid tests on
ramps and improve skid
resistance of pavement
where needed.
Emergency contract
sold (project 9075-04)
and work completed.
New interchange at I-90
and SR 615 should
alleviate congestion
along the SR 306
corridor
58
57
1.72
35
30
14.29
83
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]
84
Appendix II
AID Tree Diagram for Rear – End Crashes
85
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86
The keys to read the following figures are:
SPEEDLIMIT = Speed Limit in miles (1 mile = 1.6 km)
ADTTOTAL= Average Daily Traffic
POPDEN = Population Density (within a radius of 1.99 miles (3.2 km) of the begin
log county)
LANES = No. of Lanes
ROADWAYWIDT = Roadway Width in ft. (1 ft. = .0348 m)
SURFACE_WIDT = Surface Width in ft. (1 ft. = .0348 m)
SLIW = Shoulder Left Inside Width in ft. (1 ft. = .0348 m)
SRIW = Shoulder Right Inside Width in ft. (1 ft. = .0348 m)
MEDIANWIDTH = Median Width in ft. (1 ft. = .0348 m)
VC_RATIO = V/C Ratio
DIST_TO_INTC = Distance to Interchange in miles (1 mile = 1.6 km)
DINJFAT = Injury/ Fatal crash density
DPDO =Property damage only crash density
DTOTAL =Total crash density
DANGLE = Angle crash density
DFIXEDOBJ = Fixed object crash density
DREAREND = Rear end crash density
DSIDESWIPE = Sideswipe crash density
DROADWET =Road wet crash density
DNIGHT = Night crash density
RINJFAT = Injury/ Fatal crash rate
RPDO =Property damage only crash rate
RTOTAL =Total crash rate
RANGLE = Angle crash rate
RFIXEDOBJ = Fixed object crash rate
RREAREND = Rear end crash rate
RSIDESWIPE = Sideswipe crash rate
RROADWET =Road wet crash rate
RNIGHT = Night crash rate
87
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88
Figure1. AID Tree diagram for rear end accident density for all 12 districts of rural
highways without intersection.
89
Figure2. AID Tree diagram for intersections With One Way Stop Sign - No Control Legs
- Rear end Crashes
REAREND
Mean=0.070
SD=0.199
N=489
ADT<3760.000
Mean=0.134
SD=0.267
N=202
Mean=0.026
SD=0.112
N=287
LEFT_THR<1.000
Mean=0.194
SD=0.326
N=74
Mean=0.099
SD=0.219
N=128
ADT<7120.000
Mean=0.144
SD=0.282
N=44
Mean=0.267
SD=0.375
N=30
90
Figure 3. AID Tree diagram for T Intersections with One Way Stop Sign - Stop Control
Legs - Rear end Crashes
REAREND
Mean=0.031
SD=0.198
N=240
ADT<3190.000
Mean=0.010
SD=0.065
N=210
Mean=0.178
SD=0.516
N=30
Figure 4. AID Tree diagram for Two Way Stop Control Intersections- No Control Legs Rear end Crashes
REAREND
Mean=0.066
SD=0.277
N=313
ADT<7210.000
Mean=0.046
SD=0.125
N=283
Mean=0.256
SD=0.796
N=30
ADT<4770.000
Mean=0.032
SD=0.103
N=231
Mean=0.109
SD=0.183
N=52
91
Figure 5. AID Tree diagram for Two Way Stop Control Intersections- Stop Control Legs
- Rear end Crashes
REAREND
Mean=0.044
SD=0.179
N=313
ADT<2420.000
Mean=0.027
SD=0.104
N=280
Mean=0.182
SD=0.442
N=33
Figure 6. AID Tree diagram for Flashing Beacon Control Intersections- No Control Legs
- Rear end Crashes
REAREND
Mean=0.092
SD=0.256
N=119
ADT<5840.000
Mean=0.040
SD=0.121
N=83
Mean=0.213
SD=0.407
N=36
92
Figure 7. is for AID Tree diagram For Flashing Beacon Control Intersections- Stop
Control Legs - Rear end Crashes
REAREND
Mean=0.081
SD=0.176
N=152
ADT<3140.000
Mean=0.042
SD=0.120
N=110
Mean=0.183
SD=0.246
N=42
ADT<2030.000
Mean=0.022
SD=0.083
N=61
Mean=0.068
SD=0.152
N=49
93
Figure 8. AID Tree diagram for Signalized Intersection Legs - Rear end Crashes
REAREND
Mean=0.432
SD=0.922
N=835
ADT<14690.000
Mean=0.252
SD=0.514
N=688
Mean=1.272
SD=1.659
N=147
ADT<8140.000
Mean=0.151
SD=0.311
N=482
ADT<23620.000
Mean=0.487
SD=0.761
N=206
Mean=0.943
SD=1.209
N=106
Mean=2.122
SD=2.276
N=41
ADT<18270.000
Mean=0.645
SD=1.036
N=46
Mean=1.172
SD=1.288
N=60
94
Figure 9.AID Tree diagram for rear end accident density for statewide freeways.
DREAREND
Mean=22.499
SD=63.320
N=3813
ADTTOTAL<77220.000
Mean=8.505
SD=24.343
N=2824
Mean=62.456
SD=107.789
N=989
DIST_TO_INTC<0.030
Mean=50.377
SD=83.608
N=888
Mean=168.657
SD=200.250
N=101
ADTTOTAL<142120.000
Mean=38.306
SD=60.408
N=752
Mean=117.121
SD=142.581
N=136
DIST_TO_INTC<0.550
Mean=28.821
SD=33.384
N=43
Mean=157.948
SD=154.898
N=93
95
Figure 10. AID Tree diagram for rear end accident rate for statewide freeways.
RREAREND
Mean=1.972
SD=5.928
N=3813
POPDEN<828.656
Mean=0.987
SD=2.994
N=2995
Mean=5.575
SD=10.704
N=818
DIST_TO_INTC<0.020
Mean=4.634
SD=9.288
N=739
Mean=14.383
SD=17.231
N=79
96