DEVELOPING THE SPEED LIMIT SYSTEM IN THE LIGHT OF THE RESULTS FROM THE SPEED-LIMIT EXPERIMENT DURING 1973 TO 76

On motorways the economically optimal speed limit level would be 100 kmph according to the present valuations. On main roads the optimum lies also a little lower than the level of 1976. In northern Finland the optimal speed-limit level is about 85 kmph which is 5 kmph higher than in southern Finland. On secondary roads the level of speed limits should be 70 kmph both in southern and northern Finland according to economic calculations. A limit value could be set such that no accident risks lying above it are accepted. According to the economic calculations such limit value is 0.5 accidents per million kilometres travelled. This would mean abandoning the speed limits of 120 kmph on two-lane roads and using the speed limit of 100 kmph only when the road width is over 10 M or the 460 M sight distance percentage value is over 60%. On the same grounds the speed limits of 100 kmph should be changed to 80 kmph on roads with a high percentage of lorries. If traffic safety in winter is to be based on the same risk level, the speed limits, e.g. during the use of studded tyres should be decreased. The speed limits of 100 kmph should be changed to 80 kmph and other speed limits decreased by 10 kmph. This action would result in a noteworthy saving in costs due to pavement wear caused by studded tyres. (TRRL)