Soil and surface water along roads are exposed to pollution from motorways. The main pollutants are polycyclic aromatic hydrocarbons (PAH), mineral oil, heavy metals and salt. These pollutants originate from vehicles (fuel, wires, leakage), wear and degradation of road surfaces and road furniture (i.e. crash barriers) and the application of de-icing salts. Runoff, vehicle spray and dry deposition disperse these contaminants into the soft shoulder (verges) of the roads and surface water to a measurable distance of about 50 up to more then 150 m from the road. Despite many monitoring programs, little is known about the risks of this diffuse pollution for soil and water quality and the geochemical and physical factors which determine these risks. Also little is known about the effects of possible measures. Therefore, extensive research has been carried out at two local motorways. Specific measurements on runoff, vehicle spray and effects of measures have been carried out for one year (13 months). This resulted in several new insights. The pollutants appear to adsorb effectively to natural soils. In vulnerable areas groundwater can be protected by adjusting the policy to removing the contaminated upper topsoil of the verges. Discharges of runoff into local surface water are not recommended.
Schipper, P. N. M., Comans, R. N. J., Dijkstra, J. J., & Vergouwen, L. (2007). Runoff and windblown vehicle spray from road surfaces, risks and measures for soil and water. Water Science and Technology, 55(3), 87-96. https://doi.org/10.2166/wst.2007.076