Analyses of the accident rate on ordinary 4 lane roads have been carried out in a number of countries. On road sections without intersections the accident rate is almost the same on 4 lane roads with and without central reserves as on 2 and 3 lane roads. Thus the width of the carriageway and the presence of a central reserve have only a modest effect on the accident figures of a road section. However, central reserves reduce the number of head-on collisions which are a very serious type of accident. Level intersections on 4 lane roads seem to have more accidents than intersections on 2 and 3 lane roads with the same traffic volume according to a french investigation. This result, however, cannot be confirmed according to Danish observations.
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