Quarterly Newsletter of the Finnish Highway Transportation Technology Transfer Center, FinnT2
Address: Finnish National Road Administration, FinnT2, P.O. Box 33, 00521 Helsinki, FINLAND
Fax Int. 358 204 44 2675. E-mail: [email protected] Editor: Arto Tevajarvi, Tel. Int 358 204 44 2032
Editor-in-Chief: Jarmo Ikonen, Tel. Int. 358 204 44 2118
ENVIRONMENTAL ASPECTS OF WINTER TRAFFIC
Salting and sanding of roads as well as the use of
studded tyres adds tyre friction to the roads in the
winter. These measures also add an environmental
risk. Salt contaminates ground water while dust
from sand and material loosened from the road
surface by studs is a health risk for the populace. Diminished
friction resulted from reduced use of studded
tyres can be compensated by salting and sanding. The use
of salt can be compensated by increasing
the use of sand. The outcome is, however, a compromise between
disadvantages of the different alternatives.
The research program of Finnra, realized in 1992-95,
tried to find the optimal use of different winter maintenance
measures. One criterion was the environmentai impacts.
GROUND WATER
The risk of road salt to ground water depends
on the amount of salt spread on the road, the
location of the road with regard to the ground
water storage and the type of soil. There is a
risk that the continuous use of road sait
causes concentration of salt at the bottom of a
ground water storage thus contaminating the
water imperceptible. Results of a groundwater
model showed that chloride concentrations
stay rather low at water intakes, if the amount
of salt used remains at its present level
(approximately 10 tons per kilometre per year).
The salt coneentrations were higher approaching
the highway and, consequently, the Finnish
limit of 100 milligrams per litre of chloride
in drinking water may be exceeded if 20 tons
of road salt is appiied per kilometre per year.
Road salt is a problem mainly in the southern
part of Finland where heavily trafficked roads
are situated on gravel eskers. The situation is
worst when the road is situated lengthwise on
the esker. The coarser the material is of an
esker, the higher is the flow of ground water
and, thus, concentration of salt is slower.
Likewise, the bigger the ground water storage,
the slower the salt concentration. Unfavourable
situated dense soil stratum may guide salt
concentrations in ground water. Some wells in
moraine areas have been contaminated by
road salt.
Calcium magnesium acetate (CMA) appears to
be the best compound to substitute natrium
chloride (NaCl) in de-icing. CMA has less
environmental disadvantages, but in the
Finnish cilmate and water system oxygen
shortage caused by acetate may greatly
restrict its use. CMA is also expensive.
Environmental impacts of road salt can be kept
under controi by protecting the most hazardous
areas, and by minimal use of salt.
DUST
Replacing salt with sand adds dust concentration
in the air. The ultimate situation is
achieved when salting is decreased at the
same time that the use of studded tyres is
decreased. Then the amount of sand used to
ensure trafficability is enormous. Although
decreasing the use of studded tyres decreases
the material loosened from the road by studs,
it increases the dust in the air fourfold if
nothing is done to prevent dust formation. The
dust problem can be kept at its present level
by adding cleaning measures in proportion to
added sanding.
OTHER IMPACTS
Chloride from road salt accelerates corrosion
of water pipes. This disadvantage appears
much earlier than effects of sait. Low salinity
is also required of irrigation water in greenhouses.
The effects of salting on roadside vegetation is
minimal, being limited to less than 20 metres
on either side of the carriageway. Also the
effects of dust from sanding is minimal.
Reducing the use of salt decreases traffic
noise by keeping the roads dryer. Reducing
the use of studded tyres also decreases traffic
noise. The amount of noise reduction cannot
be determined.
According to monetary valuation, the socioeconomical
costs of environmental impacts
decreased when the use of salt was reduced.
The same effect results when the use of studded
tyres is reduced. The changes in socioeconomical
costs of environmental impacts
were not, however, great when compared to
other effects in scenarios. The least change
occurs when salting and the use of studded
tyres are at a minimum. This is mainly due to
the costs of cleaning the roads due to the dust.
In any case the problems in salting, sanding
and the use of studded tyres can be kept to a
reasonable level by optimising the use of
technology and knowledge of today.
KARI M�KEL�, Technical Research Centre of Finland
Contents of FinnContact 4/1995:
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