ABSTRACT

None of the examined scenarios was more favorable than the baseline situation. When searching for the socio-economic optimum, the accident costs become the most important factor. The accident costs strongly support retention of the baseline situation. i.e. the use of salt and studded tires should be continued at current levels in spite of their drawbacks.
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In Finland the use of studded tires began in the early 1960's. Finland has been and still is the leading country in the use of studded tires. In wintertime 95 % of passenger cars have studded tires. All tires must be studded if studded tires are used. Extensive pavement research work has been carried out to reduce the wear of pavements. Development has also produced studs which cause less pavement wear.

The simultaneous use of salt and studded tires causes problems. Studded tires wear the pavement and also increase harmful dust effects. In Finland, the best aquifers are situated in ridge areas from which salty water has easy access to the groundwater. Since these aquifers are not very large, even small amounts of salt may be enough to increase the salt content of the area. The possible salting of aquifers has been regarded as a serious problem. Therefore a significant reduction in road salting has been demanded, and even its complete discontinuation.

To solve these problems a large research program called Road Traffic in Winter was launched by Finnish National Road Administration. The main object of whole program was to evaluate new alternative winter maintenance scenarios for improving social benefits. The study viewpoint in project was simplified to three use levels of studded tires and three winter maintenance strategies, which together combined nine future scenarios. The ultimate scenario included both giving up studded tires and decreasing essentially the use of salt.

The Road Traffic in Winter project was divided into three main areas of research: A) Studies concerning traffic flow and traffic safety, B) Assessment of the state of the environment and C) Maintenance studies. The overall project included over 40 subprojects. The duration of the project was three years (1992-1995) and the total costs of the project amounted to ca. 3.5 million US $. The final report was published in May 1995.
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The condition of the tyres does not affect the speeds in winter time. The drivers who thought their tyres were inferior did not drive slower than others. The drivers' knowledge about the condition of their tyres was poor and their knowledge about the condition of their studs was even worse.The grip of the new light studs is quite similar to that of the older steel studs, but the wear of pavements is only about a half. The serviceable life of the light studs varies considerably between different makes. Studded tyres as a whole are better than studless winter tyres, so called friction tyres. A car equipped with ABS brakes and friction tyres is a good combination if driving under icy conditions can be avoided. The differences between studs are huge. /6/

Driver behaviour

The change to friction tyres did not affect the amount or time of driving. Drivers with friction tyres drove slower than those with studded tyres in built-up areas and at sharp curves. They also maintained a longer safety margin to the car in front. The changes were not, however, sufficient to keep the risk at the same level as with the drivers with studded tyres. In good road conditions the increase in speed of the friction tyre users can have a negative effect on traffic safety.

As age and driving experience increase the risk of less accidents decreases, but particularly the risk of severe accidents is at its greatest for young and old drivers.

Drivers are not aware of the road conditions. The road conditions are usually evaluated as less slippery than they really are. On the other hand the condition of the tyres is overestimated. Under slippery conditions, more than half of the drivers (56%) estimated the conditions non-slippery or semi-slippery. Very slippery road conditions were deemed by 13% as non-slippery and only by half of the drivers as slippery or quite slippery. /1/

Although the road conditions are considered as slippery, people do not slow down sufficiently and the risk increases. In snowy conditions speeds decrease by 4-5 kmph and in slippery conditions by 3-7 kmph. Drivers seem to take the winter speed limits as a “recommended speed“ regardless of how slippery the road surface is. /2/

Drivers in queues do not keep adequate safety margins. This is a problem especially in the capital region. In winter conditions one in every four keep too small safety margins (under 1.5 sec). /3/

Studded tyres of good condition increase safety. When studying accidents resulting in loss of life, 30% of the tyres were classified as being of bad condition (in normal traffic the percentage is 3%). /4/, /5/

Reduced salting experiments

During the reduced salting experiments in Kuopio (situated in the middle of Finland) the amount of sanding tripled. As small amounts of salt are used in the sand to enhance adhesion, the total amount of salt was reduced by 80%.

On the experimental roads, friction levels below 0.3 were twice as common as on control roads. Less than 3% of the time the friction levels were below 0.2 with no difference between experimental and control roads. /7/

During the first winter there were 27 accidents leading to injuries or death on the test roads and 25 during the second winter. These numbers correspond to the mean of the last five years (26.8). Taking into account the fact that accidents decreased simultaneously on the comparison roads, the experiment has increased the personal injury accidents by 5 %. On the roads in maintenance class I, comprising over 80 % of the test roads, the personal injury accidents increased by about 20 %. /8/
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Ground water /10/

The salt pollution of the ground water is a problem in southern Finland, where the most heavily trafficked roads are built on an esker. Roads built on top and following an esker are adverse.

In general, salt pollution develops slower in larger aquifers. When the esker material is coarser the groundwater flow velocity increases => water circulation increases => salt pollution is slower. Dense layers situated unfavourably can direct the salt pollution of groundwater.

At the coastal areas excessive intake of water can result in salty seawater pushing into the place of fresh water. In the old sea water reserves of the coastal areas the salt concentration can be high.

According to the modelling studies, the salt amount of 5 t/km/a which corresponds well to the current usage does not usually raise the salt concentration in groundwater. In some cases the salt concentration can even decrease a bit. /11/

Salt deposits at the bottom of aquifers has been dreaded. This didn't happen in the modelling studies. The sinking of salty water would seem possible only with extreme salt concentrations or very small flow velocities. Continued salting with great amounts of salt (10-20 t/km/a) will eventually lead to excessive increase of the salt concentration at small aquifers.

The environmental risks of salting can be controlled by protection of the most risky areas and keeping the salt amount as small as technically possible.

Vegetation

The study indicated that even modest use of road salt in the road region of Savo-Karjala resulted in accumulation of salt in the pine needles. However, the salt concentrations were not high enough to cause any visible injuries. According to the study the reduced use of road salt has proved to be good for the roadside vegetation.

Dust

Dust can cause breathing symptoms to people with allergies. The quartz dust from the road and sanding materials can be hazardous to health but the amounts of quartz dust remain so small that they can not form a risk factor according to the current knowledge.

Dusting and formation of wet, dirty fog can be controlled by traditional maintenance i.e. by opening up slush drains, moving snowbanks, well-timed peeling of ice from the embankments and by auxiliary measures (draining melt water, washing and brushing) as the need arises. Constructional road improvments can also be used to decrease dusting and/or assist in the maintenance needed to decrease dust and dusting.

Alternatives to road salt

CMA (calsiummagnesiumacetate) is in general similar to NaCl (sodium chloride) in anti-icing: Both can be applied using the same equipment and for similar circumstances. The dosage of CMA has to be 1.3 times the weight of NaCl. As the volume weight of CMA is about 63% from that of NaCl, one load on CMA is sufficient for about half the road length of NaCl. The effect of CMA decreases significantly at temperatures below —5 C. CMA melts slower than NaCl and it is not effective enough for packed snow or ice.

In Finland the oxygen content in aquifers is quite low. That's why CMA is not so suitable for us. CMA causes much less corrosion than NaCl.
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4. WINTER MAINTENANCE /9/

Reducing the amount of salt increased the transport hours by 1-5% and studless winter tyres by 2%. Using less salt increases the annual transport costs by 0.05-0.5% and using studless winter tyres by 0.1-0.3%.

Using less salt increases the standard deviation of the transport speed increasing also the risk of delay during winter road conditions by 5-10% and the total risk of delay by 0.5-1%. The increased transport time would have significance only when the logistics activities have developed to the level where small delays wouldn't be covered by elasticity in the logistics chain.

Discontinuing the salting almost totally increased the costs of winter maintenance of a busy road (6 000 vehicles/day) even by 50%. The costs of winter maintenance were increased also on roads with less traffic but the effects were smaller than on the busy roads.

Wet, including salty, road conditions existed for 46-49% of the winter period in coastal area and central Finland. The percentage of frost and icy road conditions in winter time was 11-13% except in northern Finland where the percentage was about 20%.

Hard packed snow wore twice as fast in the studded tyre tracks than in the control tracks as measured from the cross section areas. Softer packed snow wore at the same speed both in studded tyre and control tracks.

Two locked brakings of trucks on a road surface covered with packed snow collapsed the deceleration values. On the side of studless winter tyres deceleration values decreased by 53% and on the side of studded tyres by 36%.

The introduction of light studs would decrease rutting to 40-50% and the forbiddance of studs to 20-30% of the current rutting level.

The effect of alternative stud wears on maintenance costs was studied using the pavement management system (PMS). The long term target level of maintenance costs is 102 million US$/a based on the current rutting levels. The introduction of light studs and friction tyres would decrease the maintenance costs by 17 million US$/a. The banning of studded tyres would decrease the costs by a further 8 million US$/a. As the current situation will anyway change towards the light stud alternative on account of the current stud regulations, the ultimate effect of a stud ban would be only about 8 million US$/a.

In bridge maintenance the additional annual costs caused by winter salting are about 6 million US$ and the additional costs of corrosion damage prevention in the construction of new bridges are about 2 million US$/a bringing the total up to 8 million US$/a.
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The annual corrosion costs were calculated as 160 US$ per car. With the current passenger car base the total corrosion costs are about 300 milj.US$/a, half of it is caused by salt. The amount of salt used has a distinct effect on the corrosion costs and regional variations are great. In the calculations of total social costs the corrosion costs of cars were instead based on the protection costs and the costs were about a half of the former.
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In Finland in spite of rains, slipperiness and packed snow the drivers of heavy vehicles estimated the road conditions rather as fair than as bad. 63% of the bus drivers and 83% of the lorry drivers did not think that reduced salting impeded staying on schedule. Only 1% thought that reduced salting had hindered them quite often.

The small amount of road salt experiment in the Province of Kuopio was welcomed by the public. The experiment increased the number of people opposed to the use of salt. The use of road salt was most often opposed due to the environmental inconveniences. As expected, the representatives of the heavy traffic had a more positive attitude towards the use of road salt than the drivers of private cars. They motivated this with the increased traffic safety. The road users did not feel that the decrease in the use of road salt caused any great inconvenience. On the contrary, the attitudes of driver responsibility and driving comfort were usually increased.

The acceptance of the future scenarios specified in the Road Traffic in Winter -programme was tested using the weighting from a conjoint study. Normal road users saw that the primary alternative was very limited salt use combined with the current studded tyres and the current level of winter speed limits. As the use of salt would be decreased from the present, the environmental influences and car depreciation would be on a lower level. The top management of the Finnra preferred 50% salting from the beginning, the current policy of tyres and changing speed limits. Traffic safety and environmental issues would be emphasised, but the salt content of ground water could increase within the recommended levels and car depreciation could continue at the current level. Environmental and traffic safety experts saw reduced salting and current studded tyres as the primary alternative. They also hoped for lower winter speed limits and increased traffic safety.
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7. SUMMARY OF THE ROAD TRAFFIC IN WINTER PROJECT /13/

The baseline situation, i.e. 120,000 tons p.a. salting and 95 % of passenger cars fitted with studded tires, was representative of the actual practice at the commencement of the project in 1992. Since then, the salting of roads has been reduced (to 80,000 tons p.a.) and light-weight studs that are less abrasive to pavements are now used in new winter tires. In the socio-economic calculations it is assumed that all studded tires are fitted with light-weight studs (1,1 g).

In the socio-economic calculations, efforts were made to take account of the effects as broadly and comprehensively as possible. The calculations include the costs of road authority, the motorist, society as a whole and the environment. Cost assessments are based on the costs of preventing harmful effects, the established practice (e.g. accident costs) or, in the absence of these, the best estimates of relevant experts. /12/

The changes of socio-economic costs compared to baseline situation are presented in figure 1.

Figure 1. Summary of the socio-economic costs (mill. US$) of various scenarios examined in the Road Traffic in Winter Project.

None of the examined scenarios was more favorable than the baseline situation. When searching for the socio-economic optimum, the accident costs become the most important factor. The accident costs strongly support retention of baseline situation. i.e. the use of salt and studded tires should be continued in spite of their drawbacks. Studded tires provide added safety, especially for uncertain drivers in variable road conditions. Similarly, salting evens out variations in road conditions and provides an opportunity to travel safely and smoothly even in the winter (more information in TRB preprint number 960876/session 96, Kallberg V-P & al: Estimation of the Effects of Reduced Salting and Decreased Use of Studded Tires on Road Accidents in Winter).

The method of calculation used in this study has provided simplified answers to complex questions. All of the values were difficult to express in monetary terms. Those intending to utilize these findings should also familiarize themselves with more detailed studies, which will provide a more comprehensive view of the complexities of the field.

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/1/ Heinijoki, Heikki: Influence of the type and condition of tires and drivers' perceptions of road conditions on driving speed. Helsinki 1993. Finnra reports 19/1994, 99 p + appendix 60 p. ISSN 0788-3722, ISBN 951-47-9098-7, TIEL 3200229.

/2/ Saastamoinen, Kimmo. Effect of road conditions on driving behavior and properties of traffic flow. Helsinki 1993. Finnra reports 80/1993. ISSN 0788-3722, ISBN 951-47-8139-2, TIEL 3200204.

/3/ Roine, Matti. Driver behavior in sharp curves and queues on main roads. Helsinki 1993. Finnra 87/1993, ISBN 951-47-877-4, ISSN 0788-322. TIEL 3200212.

/4/ Roine, Matti: Accident risks in winter traffic among drivers using non-studded winter tires. Helsinki 1994. Finnra reports 69/1994, 49 p. + app. 13 p. ISSN 0788-3722, ISBN 951-726-017-2, TIEL 3200278.

/5/ Mäkinen, Tapani & al: The effect of studded tires on journeys and driver risk taking. Helsinki 1994. Finnra reports 64/1994, 55 p. + app 12 p. ISSN 0788-3722, ISBN 951-726-010-5, TIEL 3200273.

/6/ Alppivuori, Kari & al. Friction tires and studded tires in different circumstances. Helsinki 1994. Finnra 68/1994. TIEL 4000098.

/7/ Heinijoki, Heikki. Mäkelä Timo: Supplement to the winter tire report. Comparison of wear on studded tires and studless winter tires in main road and town use and comparison of their friction properties. Helsinki 1995. Finnra reports 22/1995, 41 p + app 23 p. ISSN 0788-3722, ISBN 951-726-055-5, TIEL 3200300.

/8/ Kallberg, Veli-Pekka: Reduced de-icing on rural roads in Finland - Final report. Helsinki 1995. Finnra reports 34/1995. ISSN 0788-3722, ISBN 951-726-080-6. 50 p + app 9 p. TIEL 3200311.

/9 Virtala, Pertti. The effects of studded tires on maintenance costs of asphalt concrete roads. Finra 58/1994. ISSN 0788 3722, ISBN 951-47-945-2, TIEL 3200267.

/10/ Kling, Terhi & al: Effect of road salt on ground water - modeling of transport processes. Helsinki 1993. Finnra report 65/1993, 74 p. + app. ISSN 0788-3722, ISBN 951-47-8114-7, TIEL 3200190.

/11/ Niemi, Auli & al: Groundwater contamination due to salt from highway de-icing, mathematical modeling. Helsinki 1994. Finnra reports 66/1994, ISSN 0788-3722, ISBN 951-726-013-X, TIEL 3200275.

/12/ Alppivuori, Kari & al: The sosio-ecomic effects of winter maintenance in the "Road Traffic in Winter" -programme. Helsinki 1995. Finnra Research Reports 4/1995, 78 p. + 4 app. ISSN 0788-3722, ISBN 951-726-081-4, TIEL 3100019.

/13/ Alppivuori, Kari & al: Road Traffic in Winter. Summary of publications in the research programme (in English). Finnra reports 57/1995. Helsinki 1995, 59 p. + app. ISSN 0788-3722, ISBN 951-726-124-1, TIEL 3200332E.