Research into road and street maintenance

i VTI

91 A

7985

Research into road and street maintenance

Börje Thunberg, Swedish Road and Traffic Research

Institute

Vag- 00/1

Statens väg- och trafikinstitut (VTI) o 58 1 0 1 Linköping

ISSN 0347-6049

VTIsärtryck

9 7 A

7985

Research into road and street maintenance

Börje Thunberg, Swedish Road and Traffic Research

Institute

7;' Statens väg- och trafikinstitut (VTI) 0 581 07 Linköping

Research

by Börje Thunberg Swedish Road and Traffic Research Institute

into road and street maintenance

The maintenance of roads and streets entails

activities consuming large sums of money. In

Sweden, government funds for these activities

during 1984 are expected to amount to SEK 4.3

thousand million. This figure relates to

state-maintained roads, roads operated by both state

and municipal authorities and private roads.

while employment subsidies are excluded.

Ad-ditional to this amount are the municipal

aut-horities own subsidies for maintenance. These

were estimated at SEK 2.4 thousand million in

1981. Taxpayers are therefore obliged to pay a

great deal of money in order to maintain

satis-factory road standards.

In recent years, road

mainte-nance authorities and other bodies have been forced to

become increasingly

cost-conscious and to ensure that

the money spent on mainte-nance is used in the most ef fective way. Research work in the area of road and street maintenance must quite simply be regarded as an aid to increase the efficiency of maintenance. Since these ac

tivities involve several

thou-sand million SEK every year, there should be considerable opportunity for increased economy through

rationaliza-tion.

The amounts mentioned

above reflect only the direct

costs of the road

maintenan-ce authorities in materials and

1)

Is the current orientati-on and level of

mainte-nance optimal?

labour. lt is interesting to look at the relationship between the costs of road users and road maintenance authoriti es. Figure 1 shows the distri-bution between cost compo-nents according to the valua tion principles applied by the National Road Administrati-on.

Since we know that diffe-rent maintenance measures have varying effects on fuel

consumption, vehicle wear,

road accidents etc, it is es-sential that decisionmakers appreciate this when consi dering changes in road and street maintenance. lt is especially important to apply principles of social economics and to take into account not only the costs of the road

2)

Analyse and evaluate

alternative orientation

and level of road main-tenance - different pac-kages of measures. Cost index

0,50..

0,40

Time cost 0 , 30-0 2 30-0_ Accident cost 0 ,10- Maintenance cost

l

m_

Vehicle cost V..

Road user costs

l \ T...

Road authorities costs

Figure 7. Example of the distribution of annual costs of traffic ac-cording to the valuation model of the National Road Administrati-on. Rural roads with daily traffic of about 7,000 vehicles.

maintenance authorities but also those of the road user,

as well as other possible costs.

Planning and

decisionmaking

prob-lems

Road and street maintenance should be regarded as a col-lection of planning, decision making and implementation problems where the road aut-hority seeks an orientation and level of maintenance such that the total social costs are minimized. An example of the decision-making problems can be

fo-3)

Choose and implement

new directives for

ori-entation and level

ofro-(After a certain time - perhaps 5 - 10 years - the chain is repeatedl r +

: No

l

I

I Yes lar don't know) l

l

l

.

.

I Continue wrth present ' routines and practice

I l l l l_ ad maintenance.

Figure 2. General diagram of the decision-making and planning situation of the road

aut-hority.

und in the balancing of road maintenance in winter betwe-en heavily and lightly used ro-ads.

Figure 2 provides a simple description of how the decisi-onmaking and planning situa tion of the road authority may be defined. The figure is cha-racterized by anapproach ba-sed on principles of automa-tic control, where maintenan-ce activities are seen as a pro-cess to be guided towards certain desired goals.

For the road authority to perform its tasks satisfactori-ly, both in planning and in implementation, it must be familiar with the relationship between different maintenan ce measures or combinations of measures and their effects, the current situation

regar-ding road maintenance, and

methods and models for eva-luating the benefits and costs for the road user and road authority.

Against this background,

the task of research in road and street maintenance sho-uld be to provide the decision-maker with a factual basis for performing the pro-cesses outlined in Figure 2.

Need for coordination

The Transport Research De-legation (TFD) has noted the need for research in road and

Proportion % n lce or 100 - snow conditi-fans 50 Wet SUI" Dry face 8 1, §2 = unsalted roads S7, 82 = salted roads Figure 3. Surface conditions

on salted and unsalted roads.

street maintenance. The TFD has appointed a committee both to follow up and mana-ge TFD-financed research and development projects in this sub-area, and to promote the coordination of such arch in Sweden. Since rese-arch into road and street ma-intenance in Sweden is sup-ported by at least 15 different bodies and authorities, most of those involved realize that some form of coordination is required. The committee in cludes representatives of the National Road Administrati-on, the Investigative Com-mittee for Maintenance Costs, the Swedish Road and Traffic Research Institute and the Association of Local Authorities. Much emphasis has been placed by the Com-mittee on the importance of bringing together researchers and road authorities. Rese-arch into road and street ma-intenance can be described as "everyday research , in which it is essential to be fa-miliar with actual conditions regarding road maintenance.

Current research at

the VTI

It is difficult, if not impossib

le, to completely separate re-search into road and street maintenance from other rese-arch concerning roads and streets. Many of the results from the former are applicab-le to other aspects of the road

authorities tasks, such as

re-gulations for road constructi-on, project studies and gene-ral road planning.

The research into road and street maintenance which has so far been carried out at the VTI has mainly involved

con-:- Clear

. [road

conditions on rural roads. In

brief, the Institute s research

work in this area can be desc-ribed as follows:

O Development of measu-ring systems and methods. Methods and equipment for determining road condition regarding rutting, cracking, bearing capacity etc.

0 Determination of changes in road condition. Data indi cating changes in the

functio-nal standard of roads, mainly

their technical characteristics such as friction and bearing capacity, is collected and sto-red using the equipment mentioned above.

. Investigation of road safe-ty and other road user ef-fects. Studies of how chan-ges in procedures such as winter maintenance influence road safety, journey speed and fuel consumption.

0 Development of materials and technical application. Self draining pavement ma

terials, emulsion concrete,

steel fibre in asphalt concrete and chemical and mechanical anti-skid measures are exam-ples from this area.

A more detailed descripti-on of the Institute s studies of "Tests on unsalted roads is given below. The work has been commissioned by the National Road Administration (W).

Tests on unsalted

roads

The background to this proj ect is the debate which has continued with varying inten-sity for several years regar-ding the advantages and di-sadvantages of road salting.

Proportion %

1001

I / 5O - Unsalted road, I / I ,0 I ~ / / / Salted road 0 4 . 0 0 , 5 J 1 | - v ' 4 ' 1 ,0' Friction (Wheel tracks} Figure 4. Number of hours du-ring which road friction was be-low a certain value.

Over the years, road authori-ties have tested various tech-niques for salt spreading, as well as varying the amount of salt and changing the directi-ves for when and where sal-ting is to be performed. Be tween winter 1980/81 and winter 1982/83, the W and the VTI studied the consequ-ences of omitting salting on a number of larger roads in the

county of Östergötland. The

project took up the following questions: 0 Road condition Friction Journey speed Road accidents Road wear Concrete damage

Forced stops by heavy ve-hicles on hills

O Corrosion

O Dirtiness of the road

0 Road user opinion on salted/unsalted roads

0 Road authorities costs

Up to autumn 1983, work on the project had been

do-cumented in the seven

re-ports mentioned in the refe-rence list. The following

diag-ram illustrates some of the re-sults.

In terms of road condition,

the tests show that salting le-ads to an increase in the sur-face area of clear road of just over 10 units, see Figure 3.

Road surface friction is, of

course, also affected. Figure 4 shows that the unsalted ro-ad has a lower coefficient of friction than the salted road for longer periods.

Figure 5 illustrates an example of the variation in friction that may occur with the use of different types of pavement. Changes in the friction level and an accom-panying increase in the risk of skidding may thus become dramatic under certain condi-tions. In this case, the increa se is explained by differences in the surface structure be tween the two pavements.

Speed (km/h)

100 AL

cars

" T _lorries F 1; 1 , 0 Friction 04J1JI1411 0 0,5

Figure 6. Traffic speeds at diffe-rent levels of road surface fricti-on.

With regard to traffic spe-eds, it has been found that car drivers pay greater atten-tion than Iorry drivers to poo-rer road surface friction (Figu-re 6). Although car drivers lo-wer their speed in conditions of reduced friction, this is in-sufficient for the car's

stop-Friction

L Surface treatment . Asphalt concrete

"0 "

+ M

l

I I 0 , 5 __ 0 1 J 1 1 1 1 ¥ 100 200 300 400 500 600 Road coordinate (metres)

Figure 5. Example of friction values measured on different pavement types. (Road 55, wet new snow, un-salted road surface).

ping distance to be affected, see Figure 7.

With regard to road safety,

no definite conclusions can

be drawn owing to the inade-quate material. A tendency towards an increased number of accidents can, however,

be seen on the hilly, unsalted test roads.

Chemical anti-skid

measu-res increase vehicle corrosion

greatly, see Figure 8.

Stopping distance (metres) l

200

100

0 0 ,5 1,0 Friction Figure 7. Stopping distances for cars at different friction levels (rural road with 70 km/h speed limit).

Salting leads to an increase in road wear. Our studies in-dicate that 10 - 20% more wear can be expected on sal-ted roads compared to unsal-ted roads. This is largely exp lained by a higher traffic volu-me under conditions with cle-arroads.

References

Research on maintenance of roads and streets. State of the art report and need for future research. VTI Meddelande 328, 1983.

Streets and roads. Main report. Swedish Association of Local

Aut-horities and the Investigative Com

mittee for Maintenance Costs, 1982.

Experiments with unsalted roads, winter 1980/81. Speed adaption by motorists to various road and fricti-on cfricti-onditifricti-ons. VTl Meddelande 301, 1982.

Experiments with unsalted roads, winter 1980/81. The effect on the state of dirtiness of the road. VTI Meddelande 302, 1982.

Experiments with unsalted roads,

Corrosion (metal loss in grams per m) m2)

p

Salt<\road

Saltoad

200 _

\

\

Unsalted road

"5 ? te '08

0

r

\\\

i;

\\\

Road pair No. 1 Road pair No. 2 Figure 8. Corrosion loss for untreated test panels when driging on unsalted and salted roads respectively.

winter 1980/81. The corrosion in fluence of road salt on vehicle chassis. VTI Meddelande 303, 1982.

Experiments with unsalted roads, winter 1980/81. Drivers attitude to winter road maintenance. VTI Meddelande 304, 1982.

Experiments with unsalted roads, winter 1981/82. The effects on ro-ad friction and roro-ad condition. VTI Meddelande 351, 1983.

Experiments with unsalted roads during winter 1981/82. The corrosi-ve effects of road salt on corrosi-vehicle underbodies. VTl Meddelande 353, 1983.

Experiments with unsalted roads, winter 1981/82. Lorry drivers opi-nion on road maintenance and anti-skid precautions. VTI Meddelande 354, 1983.