Speed Choice : The Driver, the Road and Speed Limits

Abstract: Speed choice is one of the more characteristic features of driver behaviour. The speed a driver chooses to travel at determines the degree of difficulty he or she operates under. Higher speeds lead to more accidents, higher accident risk and more severe consequences of an accident. The present thesis examines factors that are associated with drivers’ speed choice. Repeated measures of drivers’ speed showed a reasonably high correlation, but also that stability in speed varied with road layout between measurement sites. Effects of police enforcement were studied on roads with temporary reduced speed limits (from 50 km/h to 30 km/h) during school hours. Lower speeds were found on roads with enforcement and drivers observed on one such road showed a higher perceived probability of detection than did drivers observed on a non-enforced road. However, in a laboratory study higher driving speeds and lower accident risk was associated with enforced roads. Drivers not informed about existing speed limits overestimated the limits to a large extent and chose driving speeds above the limit as did drivers informed about the limits. In an on-the-road survey, fast drivers reported higher driving speed, thought a higher percentage of other drivers were speeding and had a more positive attitude towards speeding than did slower drivers. The results suggest that drivers’ travel speed is influenced by road factors, other road users and enforcement. Furthermore, drivers’ own judgements of what is an appropriate speed are also important for speed choice.