Speed Limit Increase Research Articles

Intervention analysis for the impacts of the 65 mph speed limit on rural interstate highway fatalities

The impacts of increased speed limits on highway safety have received increasing public concern since Congress passed the Surface Transportation and Uniform Relocation Assistance (STURA) Act. This research is conducted in response to such concerns, but focused only on fatalities. A multiplicative time-series model is proposed to capture the stochastic fatality pattern based on the long-term nationwide fatality data “before” the speed limit change (January 1975–March 1987). This long-term fatality model along with the 2-year “after” information (April 1987–December 1989) is then used to detect the possible impact pattern. The results of intervention analyses indicate that the increased speed limit had significant initial impacts on highway fatalities at the nationwide level. Such impacts, however, decayed after about a 1-year “learning period.” To minimize the effects of data aggregation on the estimation, all states in the data set are further classified into five distinct groups of similar characteristics. The same procedures for developing the long-term fatality model and intervention functions are applied to each group of states. An extensive analysis of six intervention patterns and their sensitivity to various presumed beginning intervals reveals that some large states, such as Texas, California, and Illinois, are insensitive to the speed limit increase. For relatively small states, the interstate highway fatalities have indeed increased significantly since the implementation of 65-mph speed limit. The level of impact, however, is much less than that exhibited in the data because other exogenous factors also contributed to the increase in fatalities since 1986. It should be noted that the major conclusion of a decaying effect of the speed limit is based on only 2 years post data, a conclusion that might well be changed as additional data become available.

Changes in speed and speed adaptation following increase in national maximum speed limit

Abstract This study replicates a 1985 study showing that drivers adapted to freeway speeds travel faster on roads connecting with the freeways than do other drivers on the same roads. In addition, the study indicates that travel speeds on these freeways were faster in 1988 even though they had retained the 55 mph (88 km h ) limit and were distant from highways authorized for the 65 mph (105 km h ) limits. These findings suggest that allowing higher speeds on some highways not only causes higher speeds on local, connecting roads through speed adaptation, but also may cause higher speeds on other, unconnected and distant roads through some indirect process of speed generalization.

The Effect of the 65-mph Speed Limit on Fatalities in New Mexico

To the Editor.— The article by Gallaher et al 1 is interesting, but I take issue with their conclusion that perhaps the increased speed limit should be reconsidered. The question is not whether the fatality rate increases a bit with higher speed limits. Although various authors have drawn different conclusions, it should be no surprise if it does so. The question is whether the medical profession, reeling under the oppressive weight of Big Brother, has any business endorsing Big Brotherism on the highway or anywhere else. The increased fatality rate that Gallaher et al purport to have identified involved primarily single-car accidents. So drivers who now elect to drive faster are primarily endangering themselves and, at worst, their own loved ones. Each and every one of the benefits of our modern society has with it some attendant risk. If cars were outlawed entirely, 50 000 fewer people a year would

The Effect of the 65-mph Speed Limit on Fatalities in New Mexico-Reply

In Reply. — Our study suggesting an increase in motor vehicle mortality associated with raising the speed limit to 65 mph on rural interstates is consistent with other such studies. Baum et al 1 have shown that fatalities on rural interstates in the states with increased speed limits in 1987 were conservatively estimated to be 15% higher than they would have been if the states had retained the 55-mph limit. (Among states that retained the 55-mph limit, fatalities on rural interstates were 6% lower than expected.) Mr Baxter's hypothesis of migration of traffic from noninterstate to interstate highways in New Mexico is an interesting one that is not substantiated by New Mexico crash data (Table 2). The geography of New Mexico is such that there are few alternative routes that parallel the state's three interstate highways, so drivers have little choice of routes for destinations along interstates. Another point against Mr

The effects of the new 65 mile-per-hour speed limit on rural highway fatalities: A state-by-state analysis

This paper examines the effects of the new 65 mile-per-hour (mph) speed limit on U.S. rural highway fatality counts. Separate analyses are conducted for each of the 40 states that had adopted the new (higher) limit by mid-1988. Using monthly Fatal Accident Reporting System (FARS) data from January 1976 through November 1988, time-series regression equations—including policy variables, seasonal variables, and surrogate exposure variables—are estimated for each state. The results suggest that the new laws have increased fatalities on both rural interstate and rural noninterstate highways in most states, but also that these effects differ substantially across the states. For rural interstate fatalities the estimates suggest a median (among the 40 states) effect of the increased speed limit of roughly 15% more fatalities; the median estimates for rural noninterstates suggest a 5% increase in fatalities due to the increased speed limits. Estimates such as those reported here should be revised as more information becomes available.

Motor vehicle crash fatalities in the second year of 65 MPH speed limits

In 1987, the federal government relaxed the 55 mph (88 km/h) national maximum speed limit, permitting states to post 65 mph (104 km/h) speed limits on rural interstate highways. By the end of 1987, 38 states had done so; and two additional states followed suit in 1988. It is estimated that the higher speed limit caused motor vehicle crash fatalities to be 26% to 29% higher in 1988 than they would have been if the speed limit had remained at 55 mph. This translates into over 500 deaths attributable to the higher speed limits on rural interstate highways. Overall, it is estimated that more than 700 people, who would have lived had the limit not been raised, have died on rural interstate highways since states began to post 65 mph limits in 1987. The effect of the higher limit doubled between 1987 and 1988, and the 65 mph limit may cost far more in death and injury than predicted prior to the speed limit increase.

Consequences of raising the speed limit

Two methods were used to assess the potential impact of increased speed limits on highway fatalities. These were: (a) a method used by National Safety Council (NSC) in estimating the causes of decreased motor vehicles in the 1970s and (b) a method used by the National Research Council, Transportation Research Board (TRB) in reporting on 10 years of experience with the 55 mph speed limit. Applying the NSC method to 1984 fatality data resulted in estimated increases of 200 to 700 deaths per year on rural interstates depending on how much the speed limit was raised. Using the TRB method resulted in estimated increases of 300 to 450 deaths per year if each state returned to pre-1974 speed limits.

The State of American Federalism—1985

Nineteen eighty-five might well be described as having been a wild and woolly year for American federalism. In February, the United States Supreme Court, in yet another 5-4 decision, overturned its 1976 holding in National League of Cities v. Usery' and told the states to look to the political process for the protection of their interests against congressional assertions of the federal commerce power. In December, the political process produced the Gramm-Rudman-Hollings deficit reduction act, the provisions of which, if fully implemented, could create a de facto new federalism not unlike the New Federalism originally advocated by President Ronald Reagan. Most of the nation's governors responded to the year's drive to balance the federal budget by saying that the states cannot absorb deep cuts in federal domestic spending. Earlier in the year, also in February, the president had rejected a bipartisan attempt by the governors to forge a deficit-reduction compromise that would have involved a tax increase, reductions in defense spending, and a freeze on most domestic spending, including a freeze on cost-of-living increases for Social Security beneficiaries. At the same time, the Reagan administration lit another fire under the political process by urging the Congress to eliminate the remaining tax code provisions for the deduction of state and local taxes on federal income tax returns. Officials in the administration did, however, entertain the idea of supporting an increased speed limit of 65 mph for rural stretches of interstate highways in states having a mandatory seat belt law, and the Environmental Protection Agency proposed that state and local governments be given principal authority to enforce toxic air pollution regulations. The U.S. Department of Energy continued to open informational offices at sites in several states which were being considered as a possible home for a nuclear waste storage facility. Citizens living near the sites were invited to make inquiries and register comments and complaints.

Impact of Highway Metrication on Traffic Accidents and Long-Term Trends in Vehicle Speeds for Roads with Resultant Increased Speed Limits

The impact of metrication of roadside speed signs upon vehicle speeds was investigated for four different road types using concealed roadside radar. The study was conducted one year after metrication to determine whether there were any long-term changes in traffic patterns in addition to the short-term influences reported previously. There was no evidence for any tendency for drivers to increase traveled speed on roads for which metrication resulted in an increase in the speed limit. Analysis of accident statistics for the month following metrication revealed no significant increase in accident rate over that projected from nine-year accident trends. It is concluded that highway metrication does not present the safety hazard suggested by critics of the metrication program.

Schottky I/sup 2/L

Schottky I/SUP 2/L uses the principles of integrated injection logic (I/SUP 2/L/MTL) and the properties of ion implantation to obtain improved performance at the same densities as conventional I/SUP 2/L. Schottky diodes are formed in the multicollectors of the switching transistor and reduce the signal swing, thus improving the power delay efficiency. An increase in the intrinsic speed limit is also feasible. The Schottky I/SUP 2/L structure and characteristics are described and contrasted with conventional I/SUP 2/L. A model which is useful for its design is discussed. Integrated test structures which provide direct comparison between conventional and Schottky I/SUP 2/L performance have been fabricated. The experimental results demonstrate a factor of 2 improvement in power-delay efficiency of Schottky I/SUP 2/L over conventional I/SUP 2/L.