Laser road surface tester (RST)

ISSN 0347-5049

VTIsärtryck

702 1.985

Amplifier Control Panel Monitor

Power Supply

Laser Electronics

Computer Printer

Floppy Disc Drives Pulse Transducer Laser Units

The Laser Road Surface Tester (RST)

Peter W Arnberg

Presented in Washington, D. C. April 22, 7985 at the

Turner-Fairbank Highway Research Center

Veg-och ail/F "

Statens väg och trafikinstitut (VTI) . 581 01 Linköping

ISS/V 0347-6049

VTIsärtryck

102

1985

The Laser Road Surface Tester (RST)

Peter W Arnberg

Presented in Washington, D. C. April 22, 7985 at the Turner

Fairbank Highway Research Center

Vag- 00/1 afllf- Statens väg- och trafikinstitut (VTI) . 581 01 Linköping

1 INTRODUCTION

More than two thousand years ago the Roman Empire was in the process of expanding over the entire known world. In order to be able to conquor new territories as well as to maintain existing ones, a road network was

constructed which served them well. Since that time much has been

learned about the construction of roads. The stone roads built before the time of Christ were of course primitive in comparison with the smooth and paved surfaces of today's roads. One thing has not changed, however,

and this concerns the urgent need for inspecting and maintaining the

road surface. Just as was probably done during the time of the Roman Empire, even today, it is frequently the case that an inspector manually

inspects the road surface in order to investigate areas potentially requiring maintenance (see Figure 1). These inspections are Optimally

standardized to as great an extent as possible in order to avoid subjectivity and, consequently, lack of measurement reliability.

r, .

Nevertheless, the task of manually inspecting the road surface is not one

which is particularly well-suited to man. Man of today is not genetically

unlike man of the stone age. For example, perception in man is well developed with regard to tasks requiring the comparison of aspects of

light movement, important in activities such as hunting in order to be

able to see animals against a background. On the other hand, memory for the comparison of one perception with another, experienced at some other point in time, is poorly developed in man. In other words, man is poorly developed in terms of absolute perceptual judgments although rather well developed in terms of comparative perceptual judgments.

Thus, the abilities of man are best utilized in surveying and controlling

objective systems which are in turn themselves responsible for the

carrying out of the absolute judgments. The subjective assessment of

road parameters will thus always remain difficult, and further develop-ments in this area are likely to only lead to a dead end. It is thus vital

that attention instead be directed toward the development of

instru-ments for the objective evaluation of road surfaces and that this be carried out as soon as possible so that the arduous task of making these instruments as precise and reliable as possible can be begun.

2 THE LASER ROAD SURFACE TESTER

The Laser Road Surface Tester (RST) is an objective system designed for

the measurement of road surfaces. It is also a component in several

larger more comprehensive systems governing road maintenance (see

earlier presentation by Hedman 1985, see also Land et al., 1985). The system has been deveIOped by the author at the Swedish Road and Traffic Research Institute (VTI) and is financed by the Swedish National Road Administration, Swe Road, RST International and various research grants from VTI. The development of the system would not have been possible, however, without the individual efforts of members of the research team who often worked on an entirely voluntary basis.

In general, system development in the road measurement area in the past

has consisted mainly of equipment design. As the equipment developed was often rather unsophisticated, little attention was given to the development of a user interface. Computer technology, however, has made it possible to design and develop highly sophisticated systems, many of which are purposely designed with user needs such as facility of use and information quality in mind. Such systems, like the RST system, are often highly comprehensive, covering the total range of activities

from data registration and initial evaluation to data base management

systems for the decision-maker. In order for such comprehensive systems to function from a technical, human, and social point of view, extensive interdisciplinary cooperation is essential. In addition to traditional desciplines representing the technical area, the team needs to be enhanced with experts on the functioning of the human. It must also include persons skilled in helping to solve problems related to the integration of the system into society, thus including not only techni-cans, researchers, and decision-makers, but also businessmen and lawyers.

2.1 How the Laser RST functions

The Laser RST vehicle is a measurement system based upon the principle of non-contact laser sensing of the road surface (see Figures 2, 3 and 4). Continuous analysis and presentation of data is provided in the car during the measurement process. The measurements can be carried out at a maximum speed of 90 km/h. The measurements are traffic-safe and objective. They are obtained at a low cost due to the high speed at which they are carried out as well as the fact that all variables are measured simultaneously. An additional contributing factor to the low

measure-ment costs is the vehicle's high durability. For example, VTI has had the

car in function for nearly four years, and during this time few of the eleven laser cameras have required any maintenance. The computer has

never been out of order. The few problems occurring have been mainly

related to the electrical system; furthermore, these have occurred

during special measurements which were carried out at unusually low

speeds.

The faser lfghpsp er on the road surfase is mej»

er:-tad on a !;thtusensffive displacement sensor.

Eiactffcai Signals fepfessn:*be varma! position

and flight fatensity of the laser spot are recorded

and computerfpmcessed.

Figure 3 The first Laser RST built at the Swedish Road and Traffic

Research Institute in 1981. Notice the angled out lasers on

the sides of the vehicle which increase the measurement

range without making the car's width greater than that of a

normal truck.

A more recent version of the RST. This car has been used in the United States for nearly two years without any major problems.

2.2 Measurement variables

Originally, the RST measured rut depth, road roughness, distance, as well

as registering three subjective variables. The car has now been expanded

to measure six objective variables. In addition to the variables mentioned above, the RST now measures cracks, rough and fine macrotexture, and

friction (when the skidometer BVll is connected to the vehicle).

The presentation of the measurement variables can be adapted according to measurement purposes and customer needs. As the software is on floppy disks, new programs can easily be added by simply inserting a different program disk. New programs can be sent by mail and used immediately by the operator. Consequently, it is easy to adapt the output to any specific purpose at hand by carrying different programs in the car. This flexibility principle underlies a basic philosophy of the RST system. The hardware has been designed to serve as general a function as possible. The exact purpose which the RST will serve thus depends on the software used. In this way continuous development is of importance to adjust the system to any specific user group, e.g., comfort measurements

might have to be exchanged with quartercar simulation in the U.S.

measurements.

The individual measurement variables are described in greater detail

below.

2.2.1 Rut depth

The most important measurement variable is rut depth. The rut depth values are now (in most programs) determined by the differences

between the values from the cameras in the Cross Profile Sampler (CPS) (see Figure 5). A cross profile is produced for every sample and from this a maximum rut depth is calculated. The mean value of the maximum rut

depth for a road unit is presented as well as the percentage of the

maximum rut depths exceeding a certain value, e.g., 10 and 20 mm (see

Figures 6A and GB). For example, in a 100 meter road unit, 20 samples might be taken. This results in one mean value for all samples as well as

the percentage of the individual sample maximum rut depths exceeding the above mentioned figures.

The lateral position of the lasers relative to the ruts may result in a measurement error if the ruts are not flat at the bottom. Normally this measurement error is very small, but on certain roads where the ruts are

very deep, steeply inclined, and where the rut bottom profile varies, the

measurement error may be of importance.

S7

82

Figure 5 Cross profile measurements for samples. The rut depth is

the largest value of Sl, SZ, S3, etc.

Thus, an even larger concentration of laser units in the ruts may be required. It might be sufficient to statistically compensate for the measurement error from the variance of the mean cross profile, in addition to increasing sampling frequency. Simulation and road tests will be carried out in 1985 in order to further investigate this problem.

It would be advisable in future survey programs to calculate more than the maximum rut depth for each profile. Perhaps the width and

maxi-mum depth of each rut or even the whole profile could be stored.

Programs that save entire profiles are already being used for special

purposes. This would create a completely different opportunity to

monitor road deterioration and assess the need for future maintenance

measures. Whole profile measurements showing the variation between

and within the ruts may indicate what is happening in the road body. This type of variation indicates whether there is a bearing capacity problem or "only" wear from studded tires.

Obiect No: Number of measurement object, automatically counted from I to total number of objects

Measured length: Length of object

Road No: Identification of road where measurement was carried out

From: Intersection or other reference point at which distance measure ment starts - "+115 m" - indicates the length from reference point to start of the actual measurement

Towards: Intersection or other reference point towards which measure-ment is heading

Speed: Average speed at which object is measured

Roughness: Serviceability index on a nine-grade scale where "9"

repre-sents a highly uneven road

>6.5: Percentage of object which has a serviceability index greater than 6.5. This limit can easily be changed

Rut depth: Rut depth as measured (see separate sheet for principle)

> mm, > 20 mm: Percentage of object which has a rut depth exceeding 10

respective 20 mm. These limits can easily be changed

Hang, Crack, Wear: Manually registered parameters preented in terms of percentage of occurrence in an object

Figure 6A The output from an early program used in Sweden with

results analyzed continuously by the RST. This car was not provided with crack or macrotexture cameras, however.

/

Figure 68 Graphic presentation can be provided directly from the

floppy disks in order to get a picture of the road network with certain parameters, e.g., rut depth, overlaid.

10

2.2.2 Road roughness

Road roughness is perhaps the most salient variable in the road users' perceptual judgment of the road, i.e., comfort is a highly important road feature. The comfort value probably also correlates highly with many

vibration effects, e.g., damage to transported goods, wear on cars, and extra energy consumption.

The comfort evaluation used in the RST was derived from comfort ratings provided by the results from experimental studies involving a large number of randomly slected road users. The users subjectively evaluated a variety of different roads while riding as passengers in cars,

buses, and trucks (see VTI reports by Magnusson & Arnberg (1976) and

Arnberg (1982) for a complete discussion of the comfort calculation validation procedure.) The RST comfort value correlates highly with other international measures such as the Chloe. It is speed independent

at speeds between 30 and 90 km/h and relatively speed independent at

speeds between 5 and 30 km/h.

At present, road roughness measurements are carried out in both wheel tracks in all programs. Only one mean value per road unit is presented,

i.e., a comfort value where "l" is equivalent to a smooth road and "9" is equivalent to a rough road. It may be preferable in the future to carry

out between track measurements of road roughness. Instead of only providing a comfort value, the signal could also be divided into different wavelength bands. Such an analysis would facilitate a follow up of the changes in the longitudinal profile of the road over time in a better way

than is being provided in existing programs. Some types of changes in the amplitude at certain wavelengths probably indicate bearing capacity problems. It is speculated that the condition of the road structure near

the surface can be determined by the shorter wavelengths while deeper structural problems are indicated by the longer wavelengths. Further development in this area will be completed in 1985.

11

2.2.3 Macrotexture

Macrotexture influences many aspects of road performance. The measurement of macrotexture may facilitate the control and prediction

of problems related to road, tire, vehicle, and driver performance.

In the Laser RST, the macrotexture is described by two measurement

variables: "rough" and "fine". Both parameters are based on longitudinal

profiles of the road. "Rough" macrotexture covers that part of the profile including wavelengths from 10 to 80 mm. "Fine" macrotexture covers wavelengths under 10 mm and is a measurement of the stone content in the pavement surface.

The RST calculates a root mean square (RMS) value for both of the above variables every l meter. These RMS values are grouped into

different classes so that a distribution (based on the RMS value) can be presented. Mean values and classes can also be provided for any road unit (see Figure 7 for a sample printout with explanations, and Figure 8 for

the results from reliability measurements).

Measurements are made in both wheel tracks. In the future, programs

should be developed in order to double this to four profiles, as macro

12

Macrotexture output from Laser RST:

! V 0 2 0.3 0.4 0.6 0.9 1.3 2.0 . ! rms 0.2 0 3 0.4 0.6 0.9 1 3 2.0 3.0 5.0 ! macro 1 ! rough 0.61 0 0 8 55 31 5 1 0 O 0 ! fine 0.32 0 35 61 5 0 0 0 0 O 0 | ! macro 4 ! rough 0.83 0 0 2 30 37 26 6 0 0 0 ! fine 0.66 0 0 O 59 31 8 2 0 0 0 !

! Root Mean Square (RMS) macro 1 and macro 4 refer to the

specific laser camera and rough and fine refer to the

type of macrotexture that was considered. The RMS value provides information almost identical to a standard dev

iation, the difference being that the RMS value is in

terms of the units being measured in this case millimeters.

! These 10 categories are in millimeter units. The information

provided is the percentage of the road surface with a macro

texture within that range. For example, 35% of the road

surface fine macrotexture measured by laser camera 1 was

between 0.2 and 0.3 millimeters.

Figur 7 _{Sample printout for fine values}

Root Mean Square (RMS) - macro 1 and macro 4 refer to the specific laser camera and "rough" and "fine" refer to the type of macrotexture considered. The RMS value provides information which is almost the same as the standard deviation, the difference being that the RMS value is presented in the units being measured, i.e., in millimeters in the present case.

These lO categories are presented in millimeter units. The information provided is the percentage of the road surface with a macrotexture RMS within a specific range. For example, 35% of the road surface fine macrotexture mea-sured by laser camera 1 had an RMS between 0.2 and 0.3 iTnLHnneters.

L o s e r RS I" 2 13

AJA CROTEXTURE RELIABILITY

1.4

1.3

-1.2

0.5

U

_{13 5}

D

0.3 ..

0.2

_

Figure 8 Results from repeated measurements with the macrotexture

measurement system on actual roads in the United States

(road unit = 100 meters)

2.2.4 Crack measurements

The RST provides information about a sample of the road surface. No attempt is made to count every crack. A procedure that counted every crack would be prohibitively expensive, time-comsuming, and rather

unneccessary.

A sample is representative of the whole road surface and is assumed to have properties similar to that surface. Information gained from the sample should thus be the same as information gained from any other section of the road. The field of statistics is, to some extent, concerned

14

with determining the validity of a sample from an entire unit. The use of samples to obtain information about entire population is the basis of

modern scientific methodology.

The understanding of this point is basic to an understanding of the RST crack measurement. It does not count every crack because it does not sample the entire road surface. It samples only those sections that are beneath the four lasers mounted at the back of the vehicle. These four lasers are mounted at strategic locations (two in the tire tracks and two toward the middle of the road). The operator can specify 3 width and 2 depth categories for the computer to use as crack size limitation areas resulting in six categories of crack size. The cameras are connected in pairs and a crack recorded within a specified distance by both cameras is considered as transversal. Longitudinal cracks cannot be indentified as being longitudinal. Instead, they will be registered as regular cracks. It may be suitable to add additional crack measurement cameras in the future. This will provide a greater sampling of the road surface and increase the statistical validity of the crack sample ( see Figures 9, 10,

11, 12A,12E >).

The RST crack values give an indication of the severity of road cracking. They also give an indication of what size cracks (within the user determined limitations) are most prevalent.

Figure 9

15

Illustration of the four macrotexture and crack measuring lasers on the RST. In the next version of the vehicle a new laser unit has been developed which will measure all variables, including cracks and macrotexture, this being similar in appearance to the front cameras.

The crack count for each of the four cameras

Three width categories (3-6mm, 6-12mm, 12-50mm)

Two depth categories (3mm and 6mm)

Macrotexture compensation factor (for this measure 1.0)

Distance (in mm) within which cracks counted by paired cameras will be considered as the same crack

16

Sample output from the Laser RST

Crack count from Laser RST:

t > 3.0 6.0 V ' > 3.0 6.0 12.0 3.0 6.0 12.0 both MC < ! 6.0 12.0 50.0 6.0 12.0 50.0 100.0 1.0 ->crack 1 40 23 5 1 3 3 2 17 13 5 0 0 O 8 4 97 54 22 1 1 7 3 18 9 3 1 1 1 14 ! I

i

!- - The crack count for each of the four cameras

I I | I I ! I I I

' ! Three width categories (3-6mm, 6 12mm, 12 50mm)

I g ! g I

i

! Two depth categories (3mm and 6mm) !

I

Macrotexture compensation factor for this measure (1.0)

I -0 -o 0 v c a . 0 o u . u o . . 0 -o o . -n u . 0 l o c .

Area (mm) within which cracks counted by separate cameras will be considered the same crack (counted only once)

Figure 10 _{Printout from crack measurements. The system is flexible}

and easy to use. A system with another type of output, e.g., a crack index scale of 1-9, where "l" is a road without cracks and "9" a road with extensive cracking, is presently under investigation.

CRACK RELIABILITY

Figure 11 _{Results from repeated measurements with four crack}

measurement cameras. The conformity with manually

measured cracks and with personal ratings is also high

17

Combination Camera 32 khz

Figure 12A Cracks measured in simulated conditions by the laser

camera. At 90 km/h cracks with a width of less than 1 mm

can be measured.

Combination Camera 32 khz eras-(<2

crack wz2mm dz10mm 90 km/h 68 67 66 65 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 1.323 1.325 1.327 1.329 1.331 1.333 1.335 1.337 1.339 1.341 (Thousands) sonu es [T IN ]

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3 THREE DIMENSIONAL PROFILE MEASUREMENT

Work to improve the Laser RST system for longitudinal profile

measure-ments is in progress. A laser plane system (RST-LP) for three

dimen-sional measurements has been developed (see Figure 13). The RST-LP

uses two external, stationary signal transmitters. These transmitters are

placed relative to a known fixed point (the reference point to which all data is related). The RST-LP has two receiving masts that allow the

central computer to continuously determine the exact location of the RST relative to the fixed reference point. This process provides the RST-LP with the necessary information for the accurate calculation of both longitudinal and cross profiles (see Figure 14). This will make it possible to carry out profile measurements with even higher precision and at greater speeds than is presently the case on roads, in addition to on airfields and bridges. The system will also be used in Sweden for the calibration of roughness and rut depth measurement carried out with the normal programs. Of course other simpler calibration systems are also being used for all variables in the Laser RST. It is especially important to do dynamic testing of the lasers, and a portable system for this purpose will be available in 1985.

7 $ 1* HST

The

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4 HIGH SPEED BEARING CAPACITY MEASUREMENTS BY

MEANS OF LASER TECHNIQUE

The methods so far described concern surface characteristic and surface deterioration measurement. Further developments are aimed toward

locating structural problems when the road is in a critical state but has

not yet deteriorated to the point of breakdown.

Work has been initiated using two sets of eleven laser cameras, one

preceding and uninfluenced by a wheel load and one directly following a rolling wheel load. The differences between the profiles taken before and

after the rolling wheel load will, if handled statistically correctly and with frequent sampling, show the rolling load influence on the road

surface. Current work is being carried out focusing on three-dimensional

simulation of the road body and investigating how various loads, speeds, and temperatures influence the road body. The results will then be used

to construct the Laser Road Deflection Tester.

LASER

20

5 CROSS PROFILE AND CURVE RADIUS

A non-gyro system is at present being tested for measurement of cross profile and curve radius with the Laser RST. The system is easy to handle and resonably inexpensive. It consists of an inclinometer which measures the vehicle's side angle and speed, and the curve radius is used to compensate for side acceleration. Similar systems have been

21

6 CONCLUSIONS

In order to be able to move away from subjective measurements towards

more objective measurements of road surfaces a great emphasis should

be placed on developing measurement systems for roads. The importance of interdisciplinary work in this area is being increasingly recognized. This will not only benefit the road measurement field but society as a

whole.

At one level the RST is a complete system. It is functionally independent and requires no support in order for it to be able to provide its information. This of course does not mean that the quality of the sytem cannot be substantially improved through further developments. This is the goal of the Stockholm survey in September 1985, during which four RST vehicles, as well as other types of equipment from Sweden and Finland, and ten drivers will be involved in assessing 50 road sections.

At another level, however, the RST is part of a larger system. This

larger system requires data from the RST in order to provide information necessary for road maintenance and road use at the societal level. The development of this larger system is still almost in its infancy and an extensive amount of work has yet to be carried out, e.g., experiments and statistical studies of relationships between RST variables and economically important variables such as gasoline consumption, vehicle degradation, etc. Experience and development must be incorporated into this system and it must be integrated with the road and communication systems of other countries.

The major advantage of the RST-system is its extreme flexibility. The user of the system is given the freedom to choose and adapt variables to his specific needs. Presentation and storage of data can also be modified for specific target needs. This approach to system design was selected in order to allow the RST to be easily used on an international basis, thus

allowing the development of a broad research base involving an active

22

LITERATURE

Alm, Lars Olof. Spårbildning i vägbeläggningar. Olägenheter. Kritiska spårdjup och mätmetoder. (Road pavement rutting - hazards, critical

depths and measuring methods.)* VTI Report 129, 1977.

Alm, Lars-Olof. Mätning av vägbeläggningars makrotextur för friktions-bedömning. Principer och mätmetoder. (Measurement of road surface

macrotexture for skid resistance prediction. Principles and measuring methods.)* VTI Report 163, 1979.

Arnberg, P W, Råhs K and Oberholtzer, R. The development potential of

the laser RST system and this sytern's importance to society. To be

published at VTI, 1985.

Arnberg, P W and Åström, G. Vägojämnheters inverkan på bilförares

prestation och trötthet. (The influence or road roughness on drivers'

performance and tiredness. A literature survey and a simulator

experi-ment). VTI Report 181, 1979.

Arnberg, P W and Magnusson G. Jämnhet och spårdjup samt subjektiva bedömningar vid provinventeringen 1979. (Evenness, rut depth and sub

jective ratings at the test survey in 1979). VTI Work Report, 1979.

Arnberg, P W. Inventering med vägytemätbil, Saab RST, 1980.

Invente-rarnas och föInvente-rarnas uppfattning om mätfordonet och

inventeringsmeto-derna. (Road survey carried out in 1980 with the Road Surface Tester (Saab RST). Sub report on the road engineeers and the drivers attitudes to the test equipment and the method utilized). VTI Meddelande 250,

1981.

Arnberg, P W och Sjögren L. Nordiska jämnmhetsmätare. En jämförande studie. (Evenness measuring vehicles used in Scandinavia. A comparative

study). VTI Meddelande 332, 1983.

Arnberg, P W and Sjögren, L.Nordiska friktionsmätbilar. En jämförande studie. (Friction measuring vehicles in Scandinavia. A comparative

study.)* VTI Meddelande 333, 1983.

Arnberg, P W and Sjögren, L. Nordiska spårdjupsmätare. En jämförande studie. (Rut depth measuring vehicles in Scandinavia. A comparative

study.)* VTI Meddelande 334, 1983.

Arnberg, P W. The Laser Road Surface Tester. A new road measuring

system developed by the Swedish Road and Traffic Research Institute. Paper presented in the US and Japan, December 1981.

Arnberg, P W. Litteraturgenomgång och diskussion av vägojämnheters

betydelse för komfort och prestation. (Literature survey and discussion

of the influence of road roughness on comfort and performance.)* VTI

23

Arnberg, P W and Hellström, Å. Betydelsen av "stimulusfelet" för ISO

och VDI komfortnormer vid tillämpning på vägojämnheter. (The import ance of the "stimulus error" to the ISO and VDI comfort standards applied to road roughness.)* University of Stockholm, Psychological Institution, Memorandum, 1973.

Arnberg, P W and Magnusson, G. Mätning och utvärdering av vibrationer

alstrade av vägojämnheter. Föredrag vid specialsymposiet "Helkroppsvib-rationer" 12 november 1980. (Measurement and evaluation of vibrations produced by road roughness.)* Invenjörsvetenskapsakademien, kommittén

för vibrationsfrågor, Arbetsgrupp 8 Vibrationers inverkan på män

niskan. VTI Separate impression.

Arnberg, P W, Carlsson, G and Magnusson, G. Inverkan av vägojämnhe ter. En problemanalys. (The influence of road roughness. Analysis of problems.)* VTI Meddelande 95, 1978.

Arnberg, P W, Magnusson, G and Ohlsson, E.. Mätning vid hög hastighet av olika vägkarakteristika. Problemanalys samt utvärdering av metod för vägojämnhetsmätning. (High speed measurement of different road

sur-face characteristics.)* VTI Meddelande 154, 1979.

Arnberg, P W. The Influence of Road Roughness on Drivers' Performance

and Fatigue. A paper prepared for The Conference "Truck Ride Quality and Highway Safety" by The University of Michigan, Ann Arbor, Mich.,

January 24-26, 1982, VTI Publication (Särtryck) 69, 1982.

Arnberg, P W, Carlsson, G, Djärf, L, Land, P G, Magnusson, G, Schan dersson, R, Simonsson, B, Wiman, L. Underhåll av belagda vägar (Main

tenance of Paved Roads. Current State of Knowledge and Research Needed."), VTI Publication (Meddelande) 406, 1984. English abstract.

Gynnerstedt, G. Road geometric design as a function of level of service and road users cost by traffic simulation. VTI Meddelande 192, 1980. Hammarström, U and Ericsson, E.. Samband mellan fordons kostnader och

väg och trafikmiljö. Litteraturstudier. (Effects of road design and

traffic conditions on vehicle operating costs. A study of the literature.)* VTI Report 154, 1978.

Hammarström, U. Bilars värdeminskning. Värdeminskningens beroende av

miljö, körlängd och tid. (Vehicle depreciation. Effects of road standard, mileage and age.)* VTI Meddelande 182, 1979.

Kihlgren, B. Slitage av bildäck vid körning på äldre ytbehandling och asfaltbetong. (Tyre wear caused by driving on old and used surface

treatment and asphalt concrete.)* VTI Meddelande 236, 1980.

Land, P-G. Pavement management system. Vägverket PP 36, 1985.

English version at the end of 1985.

Lilja, B and Ohlsson, E. Faktorer som medverkar till låg friktion mellan bildäck och vägbana. (Factors contributing to low friction between car

24

Lundkvist, S-O, Helmers, G and Ytterbom, U. Specific luminance

mea-surements of road markings and road surfaces in the field. Comparisons

between instruments. VTI Report 188A, 1980.

Magnusson, G. Inventering av utländska bestämmelser och standardkrav

för vägars jämnhet. (An inventory of foreign regulations and standard

demands regarding road roughness.)* VTI Report 84, 1976.

Magnusson, G and Arnberg, P W. The rating and measuring of road roughness. VTI Report 83A, 1976.

Magnusson, G, Arnberg, P W and Pettersson, H-E. Mätning och bedöm-ning av ojämnheter på grusväg. (The rating and measuring of road

roughness on gravel roads.)* VTI Report 123, 1977.

Magnusson, G and Arnberg, P W. Vägojämnhetens inverkan på broms- och

styrbarhet. (The influence of road roughness on the braking and steering

performance of cars: A literature study.)* VTI Report 134, 1977.

Nordström, O and Ohlsson, E. Description of friction test vehicle No. 5 of the Swedish Road and Traffic Research Institute. VTI Report 2, 1971. Nilsson, A and Ohlsson, E. Aqua planing Tests, 1967 to 1969. Investiga-tion of Braking AcInvestiga-tion Developed by Motor Car Wheels. VTI Meddelande

193,1980.

Ohlsson, E. Friktionsmätvagn BV 11. Handbok. (Friction measuring vehicle BV 11. Manual.)* VTI Meddelande 157, 1979.

Ohlsson, E. Friktionsmätning på rullbanor och vägar. (Friction measure

ment on runways and roads.)* VTI Report 177, 1979.

Olofsson, G. Bränsleförbrukningens beroende av beläggningens typ och

standard. En pilotstudie. (The dependence of fuel consumption on the

type and standard of the road surface.)* VTI Meddelande 152, 1979. Rähs, K. Vägjämnhetssimulatorer en funktionsbeskrivning. (Road rough

ness simulator - a function description.)* VTI Report 184, 1979.

Sandberg, U. Road Surface Characterization with Respect to Tire/Road

Noise Summary of Characterization Methods. STU-report 76-6618/77

6232/785650/79 5618, National Swedish Board for Technical Develop

-ment, 1982.

Schandersson, R. Samband mellan vägbeläggningar och trafikolyckor

1977. (Connection between road surfaces and traffic accidents in 1977.)* VTI Meddelande 242, 1981.

Sinha Brajnandan. Influence of road unevenness on road holding and ride

comfort. VTI Report 28, 1973.

_ _ _=*_c ".v_-_n__u.ADu-_M__m*_A-d.c Mu