Evolution and harmonization
of evenness evaluation
techniques
Danish Road Institute
Report 94
1999
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Evolution and Harmonization
of Evenness Evaluation
Techniques
Bjarne Schmidt
Danish Road Institute
Rapport 94
1999
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Road Directorate
Danish Road Institute
Elisagaardsvej 5
P.O. Box 235
DK-4000 Roskilde
Denmark
Telephone: +45 46 30 70 00
Telefax:
+45 46 30 71 05
e-mail:
[email protected]
web:
www.vd.dk
Title:
Author:
Dated:
Copyright:
Published by:
ISBN:
ISSN:
Evolution and Harmonization of Evenness Evaluation Techniques
Bjarne Schmidt
1999
Road Directorate, All rights reserved
Road Directorate, Danish Road Institute
87-90145-45-3
0909-1386
Contents
1. Evolution of Evenness Evaluation Techniques ........................... 4
1.1 Physical Principles for Objective Measurements ..................................... 4
1.2 Profile Measurement and Response Measurements ............................... 5
1.3 Speed dependency of measurement equipments ................................... 5
1.4 Data handling and presentation of the results of the measurements .. 6
2. The usage of a measuring equipment ......................................... 7
2.1 Control of new pavements ....................................................................... 7
2.2 Inventory measurements .......................................................................... 7
2.3 Detailed investigations of road profiles .................................................. 7
3. Harmonization of Road Profiling equipment ............................. 8
3.1 International investigations of road profiling equipments ................... 8
3.2 Location of the test sections in the European experiment .................. 10
3.3 Test sections and number of tests performed ....................................... 10
4. The need for harmonization of road profiling equipments .. 14
Conclusion ......................................................................................... 16
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1. Evolution of Evenness Evaluation
Techniques
The evaluation of pavement unevenness can be determined subjectively by a panel of
people or by objective measurements of measuring equipment.
The subjective evaluation can be performed by letting the rating panel drive over the
pavement surface in an ordinary car.
A classic example for this evaluation technique is related to the AASHO tests in USA.
At these tests a large number of test sections were evaluated by a rating panel with
the purpose of evaluating the Present Serviceability Rating, PSR of the test pavements.
The evaluation performed by the rating panel was then correlated to objective
measurements performed by the AASHO Profilometer.
The AASHO profilometer measured the slope variance of the pavement surface and a
correlation between the objective measured surface characteristics and the subjective
evaluated rating was performed. The result of this correlation forms the well-known
Present Serviceability Index, which besides evenness includes rutting, patching and
cracking.
1.1 Physical Principles for Objective Measurements
The principles of physical measurement can be described in the following different
categories:
1. Geometric methods:
Rod and level measurements
Measurement of the difference between a straightedge and the pavement surface
Measurement with a horizontal laser beam as reference
Measurement in relation to a moveable plane
Measurement of the slope and inclination
Superposition of measurement results from laser sensors positioned on a
straightedge
2. Combination of geometric methods and accelerometer methods.
The principle of this measuring procedure is to measure the distance from the pavement surface to the chassis, either by a linear transducer mounted on the chassis and a
measuring wheel, which follows the surface, or by a sensor not touching the surface
(optical or acoustic). The movement of the chassis is determined by a double integration of the signal from the accelerometer mounted on the chassis. By summing up the
two measuring results the true profile are determined.
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3. Initial held horizontal pendulum
The angle measurement is performed by using an inertially held horizontal refe
rence pendulum.
4. Distance measurement between vehicle axle and chassis.
Using this method the relative vertical movement between the axle and the
chassis are summarised. This value is then divided by the measured distance
(this value is used as evenness index).
5. Accelerometer signals
The measurement signal performed by an accelerometer mounted on a passenger or
the vehicle is used as index of evenness.
1.2 Profile Measurement and Response Measurements
Evenness measurements can be performed by equipments, which make a “true”
geometric profile of the pavement surface, or equipments giving a more or less
representative expression of the evenness by equipments of the response type.
Well-calibrated response type measuring equipment will often be sufficient monitoring
equipment for inventory measurements in a road network. However, reliable calibration
measurements on well-defined reference pavements are necessary.
Profile measurements vary from the most simple equipment, rod and level, to the
modern high technology equipments using laser triangulation. Profile devices can be
used in all kinds of evenness measurements. The significant increase in efficiency and
accuracy over the last decade provides the ability to measure in ordinary traffic flow,
and which makes this measuring technique outstanding in relation to other measuring
techniques.
Besides reliable information on pavement evenness to be used in pavement management systems, the use of advanced profiling devices also makes it possible to study the
pavement surface more detailed by analysis of:
·
Pavements frequency distribution
·
vehicle responses and
·
dynamic influences on pavements.
1.3 Speed dependency of measurement equipments
Due to the increase in traffic volume experienced worldwide, it becomes more and
more important to limit the time used on roadworks and measurements of pavement
conditions for the sake of the road users. Measuring vehicles which measure at a
constant speed can result in traffic delays and congestions and be the reason for
hazardous situations on a crowded road system. One of the advantages with modern
profiling devices is their ability to operate at normal traffic speed and often at speeds
up to around 100 km/h.
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The technical development of the equipment has resulted in an improved quality of the
measurements. However, the results of the measurements can be influenced by other
factors, which are related to the handling of the vehicle in the measurement situation.
1.4 Data handling and presentation of the results of the
measurements
The evolution in handling the measurement data has changed from simple methods of
analogue presentation on paper to advanced data acquisition equipment which can
handle data collected at intervals of mm and cm.
One of the advantages of modern profiling techniques and sophisticated analysis programs makes it possible to evaluate the profiles in a more detailed way than was
possible few years ago. Having the profile on a digital form, represented by cm or mm
intervals, it will be possible to perform analysis tailored to the individual road administration. Simulation of different response type measuring devices can be performed by
mathematical simulation programmes in order to calculate an index traditionally used in
a road administration. The question that often occurs is whether the rut depth shall be
determined by one or the other length of straightedge. This can be tested in the
transverse profile from the equipment by mathematically modelling several length of
the straightedge in the cross profile.
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2. The usage of a measuring equipment
One of the most important issues to be clarified when planning the introduction of a
new measuring equipment is the use of it in the future. Generally it can be said that
the ability of the equipment to reproduce a pavement profile and the ability to perform
detailed measurements and analysis shall be in a reasonable relationship to the purpose
of the measurements.
The following main features can be considered for measurement assignments.
·
·
·
Control of new constructions
Inventory measurements in road networks
Detailed investigations of road profiles
- research related assignments
- measurement of test sections for calibration of other devices
- measurement of test section with special unevenness problems
Of special consideration for a measuring equipment is the transfer function, which in
relation to wavelength or frequency gives the ability of the equipment to reproduce the
amplitude of the unevenness or the profile.
2.1 Control of new pavements
In the specification for the construction of a new pavement, the type of device used to
measure the profile or unevenness is often specified. One of the issues, which should
be taken into account, is the wavelength significant to the road users. The measuring
equipment should be able to measure wavelength according to this.
2.2 Inventory measurements
Routine measurements of evenness are used to investigate the deterioration of the
pavement over time and consequently form basis for maintenance planning.
Due to the often vast amount of kilometres it is of great importance that the
measurements can be performed with a high capacity.
Also it is of great importance that the measurements can be related to a position in the
network, as this position will be used in the pavement management process.
2.3 Detailed investigations of road profiles
For research investigations, measurement of reference test sections and pavements
with special unevenness problems, it is necessary to use profiling equipment which
records the “true” profile of the pavement surface and makes it possible to perform
advanced data handling of the surface profile.
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3. Harmonization of Road Profiling
equipment
In connection with establishment of the 2nd international experiment on highspeed
profiling equipments, the World Road Association, PIARC has defined harmonization
as follows:
“Harmonization means that a method will be developed so that each profile device can
make an estimate of the “true profile” from which all indexes would be calculated.
This allows each device to report the values it normally did in the past and still
harmonize it to the common true profile. This also allows calibration of other and new
equipment since they can later be correlated to the true profile. The alternative to
harmonization is standardization, which requires that everyone must do exactly the
same procedure.”
3.1 International investigations of road profiling
equipments
For the purpose of measuring road evenness, many different equipments are available
commercially and today many of these are operating in a highspeed manner by using
laser techniques or other non-contact techniques. Most of the modern equipments are
capable of determining the longitudinal and transverse profile of the road in order to
determine rutting and longitudinal evenness. In order to determine these parameters, it
is necessary to incorporate algorithms into the systems. These results from calculating
evenness and rutting from measured profiles depend on the accuracy of the
measurement and the used algorithms. If the outcome from a measuring system is
influenced by errors, this will have a significant effect on the outcome and use of a
PM-System with purely determined maintenance strategies as a result.
In the past there have been several other studies to compare longitudinal evenness
measuring equipment. The most notable was the World Bank International Road
Roughness Experiment (IRRE) to establish correlation and calibration standards
(World Bank Technical Paper Number 45). This experiment was conducted in 1982 in
Brazil. In the IRRE, all types of evenness measuring equipment were included,
including response type systems. The IRRE also developed the International
Roughness Index (IRI). More recently studies have been conducted by SHRP in
Ames, Iowa, the Road Profiler User Group (RPUG), and UMTRI for FHWA. In
Europe several administrations have performed comparative tests to select equipment
for network surveying.
Several of these investigations have to some extent been limited to participation by
invitation, and the outcome and results have not been made publicly available as they
are commercially related.
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In 1998, the PIARC committee C1 on Surface Characteristics carried out a worldwide
experiment to investigate the performance of different high speed profiling equipment.
During the last decade, the operational effectiveness of profiling road and airfield
pavements has increased greatly due to the introduction of non-contact sensors, such
as lasers and other optical equipment. The sensors are capable of measuring the distance from a given reference point to the pavement surface at high speed. Modern
data acquisition systems and computers make it possible to process and store the large
amount of data produced by these devices. This technology can measure both longitudinal and transverse pavement profiles at ordinary traffic speed. Thus, it is possible to
avoid road closures or traffic hold-ups, which were caused earlier by slow moving
measuring vehicles.
Monitoring of evenness characteristics on road networks has become an easier task by
means of the introduction of these high-speed monitoring systems. Therefore this task
is now being carried out in a more systematic manner.
Although the basic concept of modern pavement profiling equipment is fundamentally
the same, the development of the various measuring devices has shown great creativity
around the world.
The design of the different pieces of equipment clearly reflects the policy of what is
considered sufficient information (in the different countries) when measuring longitudinal and transverse profiles. The investigation into the differences in opinion and
technology reflecting the result of the measurements of these devices is the fundamental reason for carrying out this experiment.
These issues are fundamental parameters when performing maintenance strategies
and hence they are beneficial in planning the use of resources for network
maintenance, which will benefit both the community at large and the road users. The
results of this PIARC experiment will therefore be a primary tool for road administration around the world to pinpoint exactly the device, which meets their specific
requirements for monitoring their road network.
The PIARC experiment was conducted as an open experiment. This means that road
administration etc. already having an equipment or planning to incorporate such a
device in their road monitoring fleet, will be given an opportunity to get an objective and
non commercial valuation of the equipment’s participating in the experiment and hence
present a good guidance for selection of measurement equipment’s and analysis
methods.
Three regional experiments were conducted in 1998 in Arizona USA, Hokkaido, Japan
and a European experiment with test sections in Holland and Germany.
The Danish Road Directorate participated in the European experiment with their
Profilograph; a laser based equipment with 25 lasers positioned on a measuring beam
in front of the vehicle.
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3.2 Location of the test sections in the European experiment
The test sections were located in the area around the border of Holland /Germany
As shown in figure 1 and 2.
Figure 1, Test location
Figure 2, Location of test sections
3.3 Test sections and number of tests performed
A total of 12 test sections was established and 127 test measurements were
conducted. These were divided into test sections on in-service roads and on a special
test facility owned by the DAF company.
The distribution of test sections and measurements are shown in table 1.
Test location
Road Number/ Country
number of test
sections
number of tests
E34/A67, Holland
2
21
DAF test facility, Holland
5
45
DAF test facility, Holland
Special tests
-
16
E34/A40, Germany
5
46
Table 1, Test location and number of tests performed at the European FILTER
experiment
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The measurements were conducted by
performing standard measurement by 60,
75 and 90 km/h on well-defined test
section on in-service roads. The actual test
sections were 500 metres long and had a
run-in and run-of section as guidance to
the actual test section. The layout of the
test sections is shown in figure 3.
The test sections on the in-service roads
were open to traffic during the tests,
where as the test section on the DAF
facility were in a closed environment.
Figure 4 and 5 show the view of the operator of the Profilograph during
measurement on one of the inservice test
sections and one of the DAF test sections.
Figure 4. In-service test section
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Figure 5. Test section from DAF-test track
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As seen from figure 4 and 5, guidelines were painted on the surfaces in order for the
operators to follow the same path through the different repeated runs. The guidelines
were established to optimise the possibility of the different vehicles to measure the
same longitudinal profile on the test sections. Figure 6 and 7 show the measured
profiles for the section shown in figure 4 and 5. As can be seen from figure 6 and 7 the
calculated IRI based on the profiles vary significantly from the two test sections
shown. The IRI on the in-service road has an IRI in the range of 0,8 - 1,3 m/km, which
in the definition by the World Bank ranks as new pavements. Fore the test section on
the DAF facility, shown in figure 7, the IRI is in the range of 3,2 - 3,7, which is defined
as older pavements.
Figure 6, measured profiles by the Profilograph on Section T, all runs (IRI » 0,8 - 1,3)
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Figure 7, measured profiles by the Profilograph on Section P, all runs (IRI » 3,2 - 3,7)
The test sections in the European experiment had a variety of pavement types and
evenness. From very even concrete roads to open graded asphalt pavements with
ranges in IRI from approximately 0,5 m/km to 4,0 m/km on the in-service roads to test
sections with concrete slaps, very rutted pavements etc. on the DAF test facility with
IRI values ranging from approximately 0,8 m/km to 10 m/km. This variety in IRIvalues are in the World Bank terminology described as ranging from superhighways to
damaged pavements and rough unpaved roads. The participating devices has therefore
been tested on surface evenness corresponding to almost all types of roads where it
would be feasible to perform highspeed evenness testing.
The working group under Forum of European Highway Research Laboratories will
handle the overall data analysis for the European experiment, FEHRL, organising the
experiment. It is anticipated that the results from the experiment will be published in
late 1999.
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4. The need for harmonisation of road
profiling equipments
When looking at the performance of equipments as the highspeed profiling devices, it is
of vital importance to understand what is the use for these devices. As mentioned
earlier in the paper, the enhancement of the road profiling technology has made a
significant increase in the ability to monitor road network in relation to the evenness.
As evenness is the major factor when relating road surface condition with road user
experience and cost when using the road network, this parameter is a vital piece in
setting up a jigsaw as a pavement management system.
In the Danish Pavement Management system, evenness plays the important role of
being the factor for calculating user costs in relation to the existing pavement and the
savings in user costs when applying a new pavement or performing maintenance in the
network.
User cost model in the BELMAN-system
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User cost elements:
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7LUH
3HWURO
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Figure 8, User cost model and user cost elements in the Danish PM-system BELMAN
As shown in figure 8, the user cost is of an exponential character, hence an increase in
the IRI has a high effect on the user cost. The cost in figure 8 is specified in DDK, but
the interesting point is that an increase in the IRI from 1 to 2 will double the expenses
for the user whereas an increase from 2 to 4 will multiply the expenses by a factor 5.
Also figure 8 shows how the cost elements for the user looks. The majority of the
expenses are related to maintenance and repair cost of the vehicle whereas costs for
tire and petrol do not play a significant role.
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The importance of that the profiling equipment make a reliable measurement is vital for
the optimisation process in the PM-system, and hence have a significant influence of
the use of the allocated budget. Also in the process of forecasting future maintenance
and rehabilitation works and the budget for this is highly depending on the
measurements of evenness.
The forecasting is performed by executing a series of optimisations at various budget
levels. The input to such a forecast is the current pavement condition data, as
evenness.
The importance of having correct information about the pavement conditions becomes
obvious as the current status and the future pavement condition, as a function of the
budget, are used to calculate the future need for appropriations.
In figure 9 is shown how the development in the national evenness index for the
Danish State Road network will depend on the budget for maintenance and repair from
1998 to 2008.
,5,
PLR
PLR
PLR
PLR
PLR
PLR
<HDU
Figure 9, The evolution of IRI as a national index as a function of the budget
(75 mio DKr » 11 mio US$)
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Conclusion
Monitoring of evenness characteristics on road networks has become easier with the
introduction of high-speed monitoring systems. Therefore this task is now being carried
out in a more systematic manner.
Although the basic concept of modern pavement profiling equipment is fundamentally
the same, the development of the various measuring devices has shown great creativity
around the world.
The design of the different pieces of equipment clearly reflects the policy of what is
considered sufficient information (in the different countries) when measuring longitudinal and transverse profiles. Whatever design or capability the profile measuring system
have, the fundamental objectives is to provide reliable data to be used in relation to
road standards and maintenance and rehabilitation strategies for a road administration.
These issues are fundamental parameters when performing long-term planning. Hence
they are beneficial in planning the use of resources for network maintenance, which
will benefit both the community at large and the road users. The results of the PIARC
experiment will therefore be a primary tool for road administration around the world to
pinpoint exactly the device, which meets their specific requirements for monitoring
their road network.
The PIARC experiment will provides its objectives through the following two general
objectives:
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1.
Harmonize and correlate measures of longitudinal and transverse road surface
profiles for applications in pavement construction and management.
2.
Provide a basis for the assessment of the reliability of road profile information.
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