Effect of speed limits on speed distributions and highway safety: a survey of recent literature

This paper examines recent work on the effect of motor vehicle speed limits on highway speeds and highway safety. The review is empirical and concentrates on identifying the quantitative effects that changes in regulatory speed limit policies on interstate and non-interstate roads have on the distribution of speeds and traffic safety. Among the findings, small speed limit changes on non-limited-access roads will have little effect on speed distribution and highway safety unless complemented with speed-reducing actions. Also, the 10 mph increase in rural interstate speed limits increased nationwide mean speed and speed variance by < 4 and 1 mph respectively. Further, notwithstanding higher rural interstate speed limits leading to speed adaptation on non-affected roads, the evidence is consistent with a zero system-wide effect. Implications for further research relate to the importance of controlling for confounding factors, aggregation, the use of alternative methodologies, and the importance of enforcement in affecting speed distributions and highway safety.