Factors affecting drivers' choice of speed on roadway curves

Abstract

Vehicle speeds depend on factors relating to drivers, vehicles, and the roadway environment. Operational studies show that curvature is the roadway element that is most successful in predicting vehicle speeds. If, however, a causative explanation of drivers' behavior is sought, then attitude surveys are more appropriate than traffic observations. This paper features a survey of 207 Greek drivers who were asked to rate 14 elements of the road environment as to how importantly these influence their choice of speed on interurban road curves. A comparison of responses between drivers who claimed to obey speed limits (nonviolators) and those who claimed not to (violators) shows that the latter gave significantly lower ratings to all types of signing and were generally less restricted by roadway elements in choosing their speed. Factor analysis of the data indicates that speed choice on curves can be described by four road-environment factors: separation of opposing traffic; cross-section characteristics; alignment; and signing. Separate analyses show that nonviolators are primarily influenced by the signing factor in choosing their speed on curves, while violators' speed is chiefly determined by the road-layout factor. These findings suggest that speed reduction, where necessary, could be brought about by provision of reliable signing as well as safe and consistent low-speed alignment. The four factors identified by the analysis correspond to the findings of driver-behavior studies, indicating that attitude surveys can be used as a reliable aid in forming and evaluating relevant policies, whether at a local or a strategic level.