A number of recent studies discuss the optimality of the 55 miles-per-hour (mph) national maximum speed limit (NMSL) and evaluate the trade-off of time-lost versus lives-saved resulting from lowered ...speed. These studies implicitly accept the conventional wisdom that speed kills, and slower is safer. Speed laws have evolved as limits on driver behavior rather than as signaling devices meant to coordinate it. The present analysis tests differing views of the law by examining the current effects of the 55 mph NMSL. The effects of limit-defying behavior (speeding) and the absence of coordination (speed variance) are measured. Based on the analysis of 1981 and 1982 state cross-section data, the results show that there is not a statistically discernible relationship between the fatality rate and average speed, though there is a strong relationship to speed variance. Evidence that speed laws should be viewed as devices for coordinating speed, not just limiting it, is presented.
In 1987 the U.S. government allowed states to raise speed limits to 65‐mph on some highways. We evaluate the consequences using a resource allocation perspective: the chance to drive faster ...reallocates traffic from side roads to the safer interstate highways, and a higher speed limit permits highway patrols to shift manpower from speed enforcement to other safety activities. This perspective implies that we should measure the effect of a speed limit by its systemwide rather than its local effects. We do so and find that the fatality rate dropped by 3.49%‐5.1% following the speed limit increase. (JEL A10, R40)
It is concluded that speed variance is an important determinant of the fatality rate on the roads. In addition, there is no statistically discernible effect in any regression on disagregate data.
In 1987, most states raised the speed limit from 55 to 65 mph on portions of their rural interstate highways. There was intense debate about the increase, and numerous evaluations were conducted ...afterwards. These evaluations share a common problem: they only measure the local effects of the change. But the change must be judged by its system-wide effects. In particular, the new 65 mph limit allowed the state highway patrols to shift their resources from speed enforcement on the interstates to other safety activities and other highways--a shift many highway patrol chiefs had argued for. If the chiefs were correct, the new allocation of patrol resources should lead to a reduction in statewide fatality rates. Similarly, the chance to drive faster on the interstates should attract drivers away from other, more dangerous roads, again generating system-wide consequences. This study measures these changes and obtains surprising results. We find that the 65 mph limit reduced statewide fatality rates by 3.4% to 5.1%, holding constant the effects of long-term trend, driving exposure, seat belt laws, and economic factors.
Road pricing is widely advocated as a solution to congestion problems. The underlying theory is well developed, and we even have the technology to implement it without toll booths. Only political ...barriers remain: Decision makers are reluctant to retrofit tolls on existing highways because they do not know what circumstances might make such an action acceptable to the public. This paper develops a graphical model that displays the interaction between road capacity, user demand, travel speed and toll charges. The model is then used to analyze the sources of public resistance to road pricing. Might the potential response to road pricing be predicted using data from the new toll roads now being built around the United States? Our model shows it cannot: Political success depends on the demand characteristics at the right-hand side of the demand curve, while toll road data only trace out the left-hand side of the curve. Our model also shows situations where the new toll roads are likely to generate public anger. The Appendix discusses an experimental design that uses unobtrusive measures to assess the effect of a transportation project.
PDF
