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TRANSPORT RESEARCH LABORATORY
[2no fin Lr-- H
TITLE
by
Roughness calibration studies
different measuring systems
0 Widayat. A J Adhitya and T Tool.
Overseas Centre
Transport Research Laboratory
Crowthorne Berkshire United Kingdom
C
using
1. WIDAYAT, D, A j ADEIITYA and T TOOLE, 1990. Roughness calibration studies using different
measuring systems. In: Fourth. Annual Conference on Road Engineering. Jakarta, 19-21
November 1990. Bandung~. Institute of Road Engineering. INSTITUTE OF ROAD ENGINEERING
AGENCY FOR RESEARCH AND DEVELOPMENT
MINISTRY OF PUBLIC WORKS
IRE RESEARCH REPORT 11.026.TJ.90
ROUGHNESS CALILBRATION STUDIES
USING DIFFERENT MEASURING SYSTEMS
by
Djoko Widayat, BE.
(institute of Road Engineering),
Ir. Alvin J. Adhitya, MSc.
(Bina Karya)
and
Tyrone Toole
(Transport and Road Research Laboratory)
The main text of this report was originally prepared as
a contribution-to-the-Fourth Annual-Conference on Road
Engineering, Jakarta, Indonesia in November 1990
Road Engineering Division
-Institute of Road Engineering
Bandung
INDONESIA
January 1991 CONTENTS
Page No.
PREFACE ............................................................
ABSTRACT...........................................................
1. INTRODUCTION...................................................
2. DESIGN OF THE STUDY ...........................................
2..1 Overview ......................................................
2.2 Selection of measuring systems....................................
2.3 Selection of calibration sections ...................................
3 STAGES OF THE STUDY ...........................................
3.1 General ................
3.2 Data collection..................................................
4. DESCRIPTION OF MEASUREMENT METHODS ......................
4.1 Bump-Integrator................................................
4.2 The NAASRA roughness meter....................................
4.3 The DIPSTICK .................................................
4.4 MERLIN.......................................................
5. RESULTS AN]) ANALYSIS...........................................10
i-5 1R Reults.. .. ....... 10
5.2 Correlation between measuring systems ............................. 10
5.3 Comparison with previous studies.................................. 11
5.3.1 Bump-Integrator and. RI .................................... 1 1
5.3.3 NAASRA and IRI...........................................12
6. DISCUSSION AND CONCLUSIONS...................................12
7. ACKNOWLEDGEMENTS............................................14
8. REFERENCES ..................................................... 14 9. APPENDIX A: BI 32User's Manual: A programme for calculating Bump-
Integrator Roughness Index............................A-i
9.1 Overview.....................................................A-i
9.2 Operating Manual.............................................A-i
9.2.1 Job BI : the control file .................................... A-2
9.2.2 Data file.................................................A-3
9.2.3 Output file...............................................A-3
9.2.4 Initial data counter ....................................... A-4
9.2.5 Calibrated wheel perimeter ................................. A-4
9.3 Programme listing.............................................A-4
9.3.1 Main programme ......................................... A-5
9.3.2 BIVAR22.PAS unit........................................A-8
9.3.3 BR-TNIT22.PAS, unit.......................................A-8
9.4 References....................................................A-il
10. APPENDIX B: Computation of the International Roughness Index........B-i
10.1 Overview.....................................................B-i
10.2 Format of data file.............................................B-i
10.3 Programme listing ............................................. B-3
10.3.1 IREELEV.PAS...........................................B-6
10.3.2 IRILEVEL.PAS..........................................B-9
10.3.3 Programme output.......................................B-12
11. APPENDIX C: MERLIN data processor user's manual .................. C-i
11.1 Overview ..................................................... C-i
11.2 Data preparation..............................................C-i
11.2.1 Unsorted field data........................................C-i
11.2.2 Sorted data .................... C-3 11.2.3 MERLIN.JOB : The `job` file .............................. C-4
11.3 Running the programme : MERLIN.EXE ......................... C-6
11.4 Programme listing.............................................C-6
.1- _ _ --- --- - ROUGHNESS CALIBRATION STUD)IES USING
DIFFERE NT MEASURING SYSTEMS
PREFACE
Road roughness is considered to be the most important parameter affecting vehicle
operating costs which account for a large proportion of total transport costs. Since
maintenance management systems aim to minimise total transport costs, the
measurement of roughness is of prime importance in optimising the use of available
funds for maintaining a road network.
In Indonesia one of the main tasks of the Ministry of Public Works has been devising
and setting-up an appropriate system of maintenance management. An important
part of this system is the need to measure road roughness and correct these values to
the reference standard, the International Road Roughness Index (IRI).
The reported research describes calibration studies using four measuring systems,
namely the DIPSTICK (which enables calculation of IRI), the TRRL towed-fifth wheel
Bump-integrator, the MERLIN (a Machine for Evaluating Roughness using Low-cost
INstrumentation) and the NAASRA meter. The systems tested span the range from
low to high technology (and cost) and their operating speeds are from slow to fast.
Correlation between the reference standard and the various systems are reported and
conclusions drawn on the suitability of each for use in gathering information for input
to planning or research studies. Details of the development and listings of computer
programmes used to analyse roughness data are given.
The results of the research should contribute to the advancement of road technology
-and the moire effficienit-use~ of human and-financial resources- in areas of both high and
relatively low economic development.
**Bandung, January 1991
HEAD OF ROAD ENGINEERING DIVISION,
INSTITUTE OF ROAD ENGINEERING,
Dr. Hermanto Dardak. MSc.
NIP. 110025773
i ROUGHNE SS CALIBRATION STUDIES USING DIFFERENT
MEASURING SYSTEMS
ABSTRACT
Road roughness is considered to be the most important parameter affecting vehicle
operating costs which account for a large proportion of total transport costs. --Since
modern maintenance systems aim to minimise total transport costs, the
measurement of roughness is of prime importance in optimising the use of available
funds for maintaining a road network.
Traditionally the -assessment of road roughness has been based on the riding quality
measured by an instrumented car or other suspension-type response instruments.
Such devices are, however, neither time-stable in themselves nor consistent between
similar vehicles. It is therefore necessary for their output to be calibrated against a
standard roughness scale, such as the profile-based International Roughness Index
(IRI devised by the World Bank.
This report describes calibration studies involving a number of response type and
profile-based roughness measuring systems including the Dipstick profilometer, the
MERLIN, the NAASRA roughometer and the TRRL towed fifth wheel Bump-
integrator. Correlations between each system tested are given and the suitability of
the various systems for research or planning ,purposes is discussed.
The report also contains the user manuals and descriptions of the computer
programmes devised to process the data together with programme listi ngs.
I. INTRODUCTION
In the past decade, ,Engineers and Planners in Indonesia have been pairticularly
challenged by the: task of devising and setting-up an appropriate system of
maintenance management 'Which can be. appliedd thro~ughout Indonesia.. An important
part of this has been the measurement of road roughness.
Road roughness is one of the most important inputs to maintenance management
since the level of roughness has a large effect on the cost of transportation. Its
measurement is of prime importance in optimising the use of available funds for
maintaining a road network and, thereby, minimising total transport costs
(ABAYNAYAKA et al 1977 and PATERSON 1987).
1 The measurement of road roughness has traditionally been based on the riding
quality assessed by an instrumented car or other suspension type response
instruments.
The measured riding quality, or roughness, is primarily controlled by the road
condition. Features such as potholes, rutting, corrugations, surface texture, patches
and general unevenness contribute to its absolute level.
As is commonly known, the condition of a road is not static but changes with time and
traffic and the execution of road maintenance or betterment operations. Hence
regular sur-veys need to be undertaken to monitor changes in roughness.
In research or planning studies it is essential that suitable devices are available to
enable absolute levels of roughness to be determined accurately. The output of a
device needs to be stable with time to enable changes in roughness to be identified or
else a calibration procedure needs to be employed so that the values can be corrected
to a reference standard. The International Roughness Index (WI) has generally been
accepted world-wide as the standard to which measured values are converted
(SAYERS et al 1985a).
In general the instruments used for measuring roughness can be divided into two
groups as follows:
(i) Systems which measure or sample the road profile from a static base. These
are represented by rod and level techniques, the DIPSTICK, MERLIN and the
TRRL Roughness Calibration Beam.
(ii) Systems that measure the road profile over a moving datum. This group
includes all dynamic profilometric systems including the TRRL towed fifth
-wheel-Bumnp;--inte-grator-and-the- NA-ASRA-roughness meter..
A number of the -above systems have -been examined by the Institute of Road
Engineering (WRE) to obtain correlations between the output of each and to define
their suitability. for user in both planning surveys (ie. as input to maintenance
management) and research. The requirements for the latter two activities are
different, mainly in terms of the accuracy and repeatability of output. In addition, the
level of- sophistication .and cost of-the devices-vary greatly and at this stage in
.Indonesia's. development it. is particularly important to use reliable and affordable
data collection, techniques..
This report describes the studies undertaken to derive correlations and examine the
accuracy of the following roughness measuring systems:
2 (a) the DIPSTICK (which enables calculation of IRI),
(b) the TRRL towed-fifth wheel Bump-integrator,
(c) the MERLIN (Machine for Evaluating Roughness using Low-cost
INstrumentation),
(d) the NAASRA roughness meter.
A further objective of the research was to develop' computer- based analysis
programmes and accompanying user manuals. These are described in appendices at
the end of this report.
2. DESIGN OF THLE STUDY
2.1 Overview
Two types of roughness measuring systems are presently available, namely;
profilometer systems and respons e type systems.
Instruments in the first group measure the road profile at pre-determined intervals or
points located along a wheelpath. Their speed of measurement is generally slow, being
of the order of two to three hours per wheeltrack kilometre.
The second group comprise instruments which are mounted within a suspension
system, either in a vehicle or on a trailer, and these can measure the road profile
faster, usually at speeds between 30 and 80 kilometres per hour.. However, the
disadvantage of this ~group is that the measuring systems are dependent on the
performance of the suspension system on which they are mounted and this can
change with time and. is also a function of load, tyre pressure, tyre roundness, etc..
It is necessary for results to be obtained using instruments from the first group, but
'to assess the condition of a national road system at regular intervals-for-maintenance
purposes this is not practicable. The preferred method of operation is to measure long
l1Qngths. of road using systems in group 2 and to .calibrate their output with systems in
group. 1.
In Indonesia, at. the present..time .the.NAA.SRA roughness meter is used for routine
surveys and is calibrated to the 111I standard using a DIPSTICK (EDWARD FACE
CO., undated). Normally about six short calibration sections are chosen, each 300
metres long.
3 In the joint IRE-TRR1L research programme on road deterioration the TRRL towed
fifth wheel Bump-integrator is used for measuring roughness and is also calibrated at
regular intervals using a DIPSTICK prof ilometer.
The MERLIN is a simple, low-cost device developed by TRRL (1990) to measure
roughness and has not previously been used in Indonesia. It has the potential to be
used as a calibration and roughness measuring instrument.
2.2 Selection of measuring systems
At present three internationally recognised roughness measuring devices are available
in Indonesia. They are the NAASRA car-mounted roughness meter (SCALA and
POTTER 1977), the towed fifth wheel Bump-integrator (BI) trailer (JORDAN and
YOUNG 1980) and the DIPSTICK (EDWARD FACE CO., undated). In addition, the
MERLIN apparatus (TRRL 1990) is also available. This equipment spans the range
from high to low technology and their operating speeds is from slow to fast. During
the calibration studies all four systems were used.
In relation to the World Bank's definition of roughness measurement systems
(SAYERS, et al 1985a), the available systems can be classified as follows:
Class 1 - precision profiles : DIPSTICK profilometer
Class 2 - other pr ofilometric : MERLIN
methods
Class 3 -ERI estimates from NAASRA roughness-meter and TRR.L towed
correlation equations Bump-integrator trailer.
During earlier World Bank studies (SAYERS, et al 1985b) carried out as part of the
International Road Roughness Experiment the MERLIN was not available but, since
it is profile-based, it has been grouped in Class 2.
2.3 Selection of calibration sections
Nineteen (19) roughness calibration sections have been established in the Bandung
area.
The principle aim in selecting sections was to cover both the variety of surface types
and to span the range of roughnesses encountered on paved roads in Indonesia. The
selection .process was relatively straight forward since many of the sites had
4 previously been tested and, hence, initial estimates of the roughness on these sections
were available. The data on which these were based are contained in Table 1. The
selection also took into account practical constraints, such as traffic conditions, sight
distances and geometry..
Details of the sections and the testing done on each are contained in Table 2. In each
case the effort was not uniform since the aim was also to develop a more extensive
data-base on the surface characteristics of the sections, rather than only to calibrate
the instruments. In cases where the BI, the MVERLIN or the DIPSTICK were used
then measurements were taken in each wheelpath.
The coverage of surface type with respect to roughness is given in Table 3.
As shown in the table, the spread of. roughness with respect to surface type is not
uniform, reflecting the surface conditions in the vicinity of Bandung, the high initial
roughness of penetration macadam surfaces and the relatively low roughnesses of
roads overlaid with. plant-mixes.
3. STAGES OF THE STUDY
3.1 General
Test sections were marked out along 300 metre lengths of road with the outer
wheeltrack (OWT) located at a distance of approximately 0.70-1.00m from the
pavement edge. The exact distance depended on the width of the road and traffic
patterns. The inner wheel track (IWT) was located at a distance of 1.30m from the
OWT. The purpose of the marking was to enable tests to be repeated along the same
path._-Per-manent-reference -posts were inserted at each end of a calibration section so
that the sections could be re-located in the future.
3.2 Data collection
The data collection was carried out in November and December 1989.
Between: 3. and-5 Bump-;integrator measurements were -taken in both the OWT and
the IWT of each road calibration section, at a speed of approximately 32 km/hour.
Measurements with the NAASRA roughness meter were also repeated, between 3 andA
5 times also at a test speed of 32 km/hour.
5 When using the vehicle mounted response-type systems, care had to be taken near
cross roads or junctions. Traffic Was temporarily halted during testing to give priority
to the test vehicle.
The DIPSTICK measurements were taken only once. Approximately one hour was
taken to complete each wheelpath (length = 300 in).
The MERLIN measurements were taken three times in each wheel track with each
measurement taking about half an hour.
4. DESCRIPTION OF M4EASUREMENT METHODS
4.1 Bump Inteerator
The Bump-integrator (BI), or BPR Roughmeter, was originally developed by the
United States Bureau of Public Roads. TRRL have since made a number of
modifications to improve its performance and simplify maintenance (JORDAN and
YOUNG 1980). The instrument used in this study was to the current TRRL design.
The Bump-integrator consists of a single-wheeled trailer comprising a rectangular
chassis within which a pneumatic tyred wheel is mounted, the load, tyre size and
pressure are standardised. The BI is towed by a station-wagon or similar vehicle (see
Plate 1).
During operation, the vertical movement of the wheel-axle assembly relative to the
chassis is measured by an integrator unit mounted on one side of the chassis. This is
made possible by connecting the axle to the integrator unit by a cord tied to the
cylindrical-drum-on-the integrator-unit.--Tension in-the-cord--is-maintained by a-clock-
type return spFn fitted to 'teitegrator unit. The integrator works by
accumulating the down-ward movements of the axle which are transmitted through a
clutch-system to give a uni-directional movement of a cam which then triggers the
"mkiSri4'and "breaking"of an electrical contact. The pulses of electric current which
this creates activates the counter. On -the present system one count is equal to an
accumulated downward movement of 1-inch (or 25.4 mm).
The distance the BI travels along the road is measured automatically by recording the
number of revolutions of the wheel.
Recording is made possible by having two sets of Bump-- integrator and wheel-
revolution counters together with an on/off switch and a changeover switch mounted
on an instrument board located within the towing vehicle.
6 Determination of the Bump-integrator Irregularity Index (BIr) requires the number
of counts of the bump integrator, counter, the time (in secs) and the number of wheel
revolutions to be recorded. The BIr value is then calculated as shown below.
Example,
T im e = 31 sec.
Wheel revolutions = 137.
Integrator counter = 17.
The distance the bump integrator has travelled is calculated by multiplying the
number of wheel revolutions by th~e wheel circumference :
The distance
The speed
Speed
137 x 2.18 = 298.66 m
distance
time
298.66--- --- :.m/see.
31
-9.63 in/sec
9.63 x 60 x, 60
------------- = 34.67Km/h
1000
The irregularity index is calculated as follows:
Intep-rator counter value x 25.4 x number of wheel revolutionhs in one km.
Recorded number of wheel revolutions
BIr
17x25.4 x 1000
.137 x 2.18
BIr = 1,446 mm/'Km
Measurements are corrected for speed variations to 'a standard index (BI 32)
corresponding to a speed of 32 km/h. Studies by Jordan and Young (1980) led to the
following expressions for this purpose:
7 (i) For uneven surfaces and operating speeds of 20 to 65 km/h and for even
surface and operating speeds of 20 to 32 km/h:
BI 32 = CV/2,) 0 (BIr -474) + 474 mm/km.
(ii) For even surfaces and operating speeds of 32 to 65 km/h.
BI 32 = (V32)(BIr -474) + 474 mm/km.
Where V is the measurement speed in km/h.
Applying expression (i) above to the example the standard index is:
BI 32= 1,527 mm/km.
A computer programme which was developed to calculate the corrected irregularitly
index, BI 32, is contained in Appendix A.
4.2 The NAASRA roughness meter
The NAASRA roughness meter was developed by the National Association of
Australia State Road Authorities (SCALA and POTTER 1977).
The meter is mounted above the middle of the rear axle of a saloon car. Guidelines
for its operation include the specification of a suitable vehicle, tyre pressures and
ballast (load).
The basic principle of the meter is that it sums the movement (in one direction) of the
rear axle with respect to the vehicle body. This results from the movements of a
flexible cable which is connected from the meter to the centre of the rear axle. The
cable is joined to a chain which passes over a toothed sprocket held on a shaft flitted
..witliclutches-so- th-at-the-shaft- will, onil rotate in one direction. Movements in the
shaft are transmitted by a flexible drive to a counter mounted in the front of the car.
The essential features of the-NAASRA roughness meter are shown in Fig. 1.
The output is in the form of the number of counts over a given 'distaiice and the-
roughness is expressed in counts/km.
In Indonesia the normal speed of measurement is 32 km/hour.
8 4.3 The DIPSTICK
The Dipstick Floor Profiler is manufactured by The Edward W. Face Company Inc. of
Norfolk, Virginia, USA and was originally developed for checking the evenness of
floors.
The DIPSTICK, illustrated in Plate 2, measures the surface profile along a line by
indicating level differences between its two supporting feet which are one foot, or
304.8 mm, apart. Consecutive measurements are obtained by walking (frog-
marching) the instrument along a line for the length of a test section and recording
the level difference at each placement.
Level differences measured by the DIPSTICK are usually in increments of 0.001 inch
(0.0254 mm). The standard analysis involves inputting the data into the IRILEVEL or
VERICAL computer programme and determining the International Roughness Index
(in in/kin). The analysis programme is based on the system of profile analysis derived
by the World Bank (SAYERS et al 1985).'
The VERICAL analysis programme available in Indonesia was developed by Bina
Kar.ya and Lea (1987). For this research, the original World Bank programme was
rewritten in Turbo- PASCAL. The equivalent IRE version to VERICAL is named
IR=LVEL, which requires the data to be input in level differences. A second
programme, named IRIELEV, was also written and accepts data input as elevations.
The programme listings and details of their development are contained in Appendix
B.'
4.4. MERLIN
-MERLIN- is an accronym. for- a -Machine for Evaluating Roughness using Low cost
INstrumentation. The machine was developed by the Transportfand Road Research
Laboratory (TRRL, 1990). Construction drawings for MERLIN are available on
application to TRRL or IRE.
The MERLIN is a simple, low cost -and~ easy to use instrument for measuring road
roughness.. The device,. illustrated in Figure 2, consists of a metal frame 1.8 metres
long with a wvheel aftherront afie a tal. rf~ oot at thbe rea. MNidway bbtween the two
wheels is a probe which is attached to a weighted arm to hold it onto the road surface.
9
1
1 ---- At the other end of the arm a pointer moves over a prepared chart consisting of a
series of columns, each 5mmn wide.
The device measures the vertical height difference between the road surface under the
probe and the centre point of an imaginary line joining the two points in contact with
the road surface. A movement of 1 mm of the probe moves the pointer 1 cm.
During operation the MERLIN is brought to rest at intervals equal to one
circumference of the wheel and at each consecutive location the position of the
pointer is recorded on the chart.
The results of a series of MERLIN measurements are represented by a histogram. A
typical result is shown in Figure 3. From this, a MERLIN Dispersion Value (DISP) is
derived by omitting ten per cent of the readings, divided equally between the two tails
of the distribution,and the dispersion recorded as the width in mm of the remaining
distribution.
During this research the analysis of the data was facilitated using the specially
developed analysis programmes described in Appendix C.
Research by TRRL based on computer simulations has shown that the MERLIN can
be correlated directly with standard roughness scales such as the International
Roughness Index and the towed fifth wheel Bump-integrator (CUNDILL 1990).
5. RESULTS AND) ANALYSIS
5.1 Results
A summary of the results of the measurements taken during the su rveys is shown in
Table 4.
The range of the values measured by each system is shown in Table 5. For each
system, lower values cor~respond with a smoother road, ie. good riding quality, and
higher values with poor~ riding quality.
5.2 Correlations betwedefi measurinpg systems
To establish the correlations between the various measuring systems a line of. best
`fit` was determined for 'each pair of systems using simple linear regression
techniques. Statistical coefficients and a plot of residuals were also obtained.
10 The following three correlations were examined:
(i) Towed bump integrator (BI32) versus IRI.
(ii) NAASRZA roughness meter (N) versus LIRI.
(iii) MERLIN (DISP) versus IRI.
The regression models included a linear model and a multiplicate model, as follows
Linear model Y =a +bX and
Multiplicative model Y. =ab
In each case the IRI was the dependent variable (Y) and the corresponding roughness
system the independent variable (X).
The results of the analysis are given in Table 6. In each case the multiplicative model
gave a slightly better fit. The resulting regressions for, the three multiplicative
models are plotted in Figs. 4, 5 and 6 and given below.
IRI (in/kmn) = 0.0027 BI32 0.944
IRI (mn/kmn) = 0.324 NO. 606
IRI (in/kin) = 0.153 DISPO. 796
In all cases the data sets included both the outer and inner wheelpath data. In the
case of the NAASRA-IRI correlation the IRI value used was the arithmetic mean of
each pair of wheeltracks.
Because of the limited range of roughness values within each surface type, separate
relationships were not developed.
5.'3 -Coflipari~6i sonitlh prTi~t-i-oi stuldies
5.3.1 Bump Integrator and. IRI
The particular Bump Integrator unit used in this. research has not previously been
calibrated against IRI. In previous studies by TRRL the performance of each Bump-
integrator has been assumed to be similar provided the calibration guidelines are
followed (JORDAN and -YOUNG 1980). In the International Road Roughness
Experiment (IRRE) in Brazil a standard BI was calibrated against the IRI standard.
The following expression resulte-d from these studies:
MRI = 0.0032 BIO. 89 (Cox and Rolt 1986)
1 1 The relationship derived from the present study was
IRI = 0.0027 B10.944 (This study)
where IRI is expressed in rn/kin, and BI is expressed in mm/km.
The output of the two expressions is compared in Figure 7 in which a linear
regression has been fitted to the plotted data. From the figure it is clear that the
model developed in this present study overestimates the IRI by about 30%. The
indication from this is that the performance of the present 31 is behaving in a non-
standard manner which emphasises the need for calibration studies.
The results of the earlier study and a more recent calibration survey are compared in
Figure 8. A maximum difference between the two relationships of between 12 and 3
per cent (from low to high roughness) is noticeable.
5.3.2 NAASRA and IRI
The relationships between NAASRA and IRI derived during this study and also in
May 1988 and August 1989 are compared in Fig. 9. The basic data for the early
studies is included in: Table -1. As indicated in the figure a maximum difference of
about 10 percent exists between the May 1988, the August 1989 and the November
1989 calibrations~. This difference is surprisingly small and is at the lower end of the
expected changie between successive calibrations for a single vehicle, which typically
ranges from les:s than 10 per cent to as much as 35 per cent (PATERSON 1983).
-~6-DICUSIONAI~14C ONCL-USION S- --
Statistically si~gnificant- correlations. have been obtained between. the International
Roughness' Ieidex (IRI) -detiivd fro m- DIPSTICK measurements and the three other
measuring systems tested, namely the TRRL towed fifth wheel Bumfp-integrator
trailer, the NAA'SRA car-moun'ted roughness-meter and the MERLIN.
Of the three non-standard systems only the output of the MERLIN is based on the
analysis of points along a road profile and, for a given surface type with a
correspondingly s imilar range of spectral signatures, a unique relationship will exist
with the IRI. Fu'rther work should be done to derive individual correlations for each
surface type across~a. wideir range of roughness. Following this the MERLIN, could
effectively replace. or supplement the DIPSTICK in circumstances where t he sole
purpose of the exercise is to calibrate a response type instrument.
12 Advantages of the MEI3RLIN are its low-cost, approximately 250 US dollars, and its
suitability for manufacture in local workshops. It is also easy-to-use and its output,
as a calibration device, is about 600 metres per hour. This compares with the
re latively sophisticated DIPSTICK, which costs approximately 7000 US dollars, has
an output of about 300 metres per hour and requires supporting computer software.
Although valid correlations were obtained between IRI and the Bump-integrator and
NAASRA meter it is widely accepted that these systems are not time-stable and the
output between different vehicles or trailers of the same kind can vary significantly.
This is principally because of initial differences and changes with time of suspension
characteristics. Paterson (1983) indicated that even for vehicles which are dedicated
to measuring roughness and which are maintained and used in accordance with strict
procedures the difference between successive calibrations for a single vehicle typically
ranged from less than 10 per cent to as much as 35 per cent. Differences between
vehicles of the same type would be expected to be even greater. However, in this
particular study the IRE NAASRA meter appears to have changed by only a small
amount, approximately 10 per cent over two years. On average the change in the BI
between successive calibrations was slightly less, between 12 and 3 per cent, although
this was over a shorter period and only involved two calibrations.
Although the time-stability of the NAASRA. meter was better than expected the
results do not preclude the need for both regular calibration and the use of control
sites when extended route surveys are undertaken. This is because favourable
results from a small number of calibrations cannot guarantee that the same degree of
control and measurement consistency is achieved at the operational. level. In this
context, control sites are ~sites which. are distributed throughout a network and whose
profile characteristics. have been recently measured and can, therefore, provide a
check on whether significant changes in the calibration have occurred during the
course of a network survey. The adoption of such a procedure also provides a
-measure-of-additional-qualit-y-control-which-is-independent of-the-op~erators.-
In the present IRE-TRRL road deterioration research programme approximately one-
ini-four of the monitoring sections are measured using the DIPSTICK-and BI.
Although the RI, calibrated against the DIPSTICK, provides valid measurements the
large differences between the IRI-BI relationships derived at the International Road
Roughness Experiment and the results of this study are of concern and are being
investigated.
In summing-up, response type instruments are most useful for undertaking network
surveys at fairly high speeds. However, calibration to a reference standard is
necessary and, as, the results of this study indicate, this can be achieved with a
13 DIPSTICK or a MERLIN. The choice can be based purely on cost and level of
expertise available.
For research purposes the DIPSTICK provides the precise profiles required although
the financial cost of data collection and use of human resources is high. A
combination of using the DIPSTICK and BI provides a compromise solution
particularly where control sites ar e used, and precise profiles measured.
A procedure involving calibration and control sites has been implemented in IRE-
TRRL research studies both on monitoring sections and at a network level. The
continuation of this study will enable calibration and operating procedures to be
established which will allow small changes in roughness to be accurately and
consistently identified.
7. ACKNOWLEDGEMENTS
The -work described in this r eport forms. part of the collabora~tive research project
being undertaken by the Indonesian Institute of Road Engineering and the Transport
and Road Research Laboratory.
The MERLIN and Bump-integrator used in this research are the property of the
Institute of Technology, Bandung and thanks are due to Ir. Djuanda Suraatmadja,
Head of ITB-S2 Master's Program in Highways and Transportation and to Professor
J.H. Jones who contributed to the study of the MERLIN.
-8.REFERE-NCE-S - - -
ABAYNAYAKA, S.W. et al (1977). Prediction of Road Construction and vehicle
operating costs in developing- countries. Proc. of Institution of Civil Engineers, Part
1, 62 (Aug.), London, p.419-446.
BINA KARYA and LEA,- (1987). VERICAL, Version 2.10 Operators Manual.
Direktorat Jendral Bina Marga, Bina Karya-Lea Consulting Engineers, DBM
Management Assistance Consultancy Services, Jakarta, Indonesia.
COX, J..B. and J. R. ROLT, (1986). An integrated approach to pavement design based
on 11DM-III pavement performance and vehicle operating cost relationships. Proc. of
13th ARRB - 5th REAAA Conference. Vol. 13, Part 4. Australian Road research
Board, Melbourne, p. 135-149.
14 CUNDILL, M. (1990). The MERLIN low-cost road roughness measuring machine.
Department of Transport, TRRL Research Report (in preparation). Crow-thorne
Transport and Road Research Laboratory.
EDWARD FACE CO. (Undated). The DIPSTICK profilometer : Instruction manual.
The Edward W. Face Company Inc. Norfolk, Virginia.
JORDAN, P.G. and J.C. YOUNG (1980). Developments in the calibration and use of
the Bump-integrator for ride assessment. Department of the Environment,
Department of Transport, TRRL Supplementary Report 604. Crowthorne
Transport and Road Research Laboratory.
PATERSON, W.D.O. (1983). Accuracy of calibrated roughness surveys. ASTM
Symposium on Roughness Methodology. Bal Harbour, Florida, USA.
PATERSON, W.D.O. (1987). Road deterioration and maintenance effects: models for
planning and management. The Highway Design and Maintenance Standards Series.
The John Hopkins Press, Baltimore, Maryland, USA.
SCALA, A.J. and D.W. POTTER (1977). Measurement of road roughness. ARRB,
Technical Manual No. 1. Victoria: Australian Road Research Board.
SAYERS, W.S. et al (1985a). Guidelines for the conduct and calibration' of road
roughness measurements. The World. Bank, Technical Paper No. 46. Washington
International Bank for Reconstruction and Development.
SAYERS, W.S. et al. (1985b). The International Road Roughness Experiment
Establishing orelations -and a calibration standard-for-measurements. -The World
Bank, Technical Paper No. 45. Washington' D.C. International Bank for
Reconstruction and Development.
T.R.R.L. (1990). MERLIN. A Machine for Evaluating Roughness using Low-cost
INstrumentation. Transport and Road Research Laboratory, Leaflet LF 2027.
Crowthorme :Transport and Road Research Laboratory.
CROWN COPYRIGHT. The views expressed in- this paper are not necessarily those
of the Department of Transport, United Kingdom. Extracts from the text may be
reproduced, except for commercial purposes, provided the source is acknowledged.
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