When new roads are built today, the Swedish official strategy is to leavein situ the cultural layers that are not directly affected by the road construction, rather than to excavate the entire layer even if it stretches outside the verge of the planned road. This strategy has its roots in the Act concerning Ancient Monuments and Finds and is built on the assumption that the soil layers protect the archaeological artefacts far better than the national archives and museum shelves. The cultural layers are looked upon as a national archive in situ. However, recently excavated metal artefacts generally exhibit greater deterioration than those excavated many years ago, implying that recent pollution is responsible for accelerating thecorrosion. Unfortunately, the de-icing salt used in winter maintenance operations does not stay on the road surface, where it has its desired effects on traffic safety and accessibility, but is transported - by different mechanisms - to the sides of the road where it may have undesired effects on e.g. vegetation, soil and groundwater, and possibly also on archaeological artefacts (metal, wood, cloth, bone, leather etc). The mechanisms responsible for the roadside exposure to salt are influenced by many factors such as wind, road surface condition, topography and surrounding vegetation. In many cases the salt will spread several tens of meters from the road,and in the worst cases raised levels of salt may be found up to some hundred meters from the road. When transported by groundwater, salt may be moved very far and may reach cultural layers in discharge areas where the ground water reaches the soil surface layers. This paper describes the problem of exposure to de-icing salt and the possible corrosion of archaeological artefacts with reference to a literature review and suggests some ways in which the extent of the suggested problem can be investigated by field studies under semi-controlled conditions and by a GIS survey. For the covering abstract see ITRD E143097.
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