The objective of this study is to estimate the safety benefits of studded tyres. The study was carried out in the periods 1983-1999 for Iceland's capital city, Reykjavik, and 1992-1999 for the country's rural areas and other municipalities. The accident databases contained information on all police-reported accidents, 35,848 for Reykjavik and 14,385 for other parts of the country. A comparison was made between summer tyres and winter tyres (studded and nonstudded). The database was split up into "perpetrators" (those making a mistake leading to an accident) and "victims" (those involved in an accident without causing it). The tyre types used by the victims were an indicator of the actual average use. The use of summer tyres during the winter was obviously dangerous. This applied for both urban and rural areas alike. A straightforward comparison between perpetrators and victims in urban and rural areas seemed to show that studded tyres provided a considerable excess of safety. The circumstances were then split into dry and wet road surfaces, on the one hand, and ice and snow conditions, on the other. The group using studded tyres continued to show a similar excess of safety even though the equipment (the studs) should provide safety gains for ice and snow conditions only. This indicates that the drivers are safer and not the equipment. However, there is a slight, unexplained difference, which could be related to the use of studded tyres. It is important to split the obvious safety gain from using studded tyres into a behavioural factor and an equipment factor. Studded tyres certainly provide more grip in icy and snowy conditions than non-studded tyres, but in good conditions, they may be even worse than non-studded tyres. The results shown here indicate that behaviour is a much greater factor than equipment, but a small proportion of the safety gain is nevertheless attributable to the equipment. While the behavioural factor is over 20 per cent, the equipment factor is under 5 per cent in urban areas. The same numbers are over 30 per cent and over 10 per cent for rural areas, respectively. On the grounds of this safety study, ways should be sought to limit the use of studded winter tyres in the urban Reykjavik area. To maintain accessibility during winter, the rest of the country, entailing mainly rural areas, should not impose restrictions.