Long-term Effects of Repealing the National Maximum Speed Limit in the United States

Lee S. Friedman, PhD; Donald Hedeker, PhD; Elihu D. Richter, MD, MPH

Disclosures

Am J Public Health. 2009;99(9):1626-1631. 

In This Article

Abstract and Introduction

Abstract

Objectives. We examined the long-term effects of the 1995 repeal of federal speed limit controls on road fatalities and injuries in fatal crashes.
Methods. We used a Poisson mixed-regression model to assess changes in the number of fatalities and injuries in fatal crashes between 1995 and 2005 on rural interstates, where all US states have raised speed limits since the repeal, as well as on urban interstates and noninterstate roads, where many states have raised speed limits.
Results. We found a 3.2% increase in road fatalities attributable to the raised speed limits on all road types in the United States. The highest increases were on rural interstates (9.1%) and urban interstates (4.0%). We estimated that 12545 deaths (95% confidence interval [CI]=8739, 16352) and 36583 injuries in fatal crashes (95% CI=29322, 43844) were attributable to increases in speed limits across the United States.
Conclusions. Reduced speed limits and improved enforcement with speed camera networks could immediately reduce speeds and save lives, in addition to reducing gas consumption, cutting emissions of air pollutants, saving valuable years of productivity, and reducing the cost of motor vehicle crashes.

Introduction

In 1974, the federal government passed the National Maximum Speed Law, which restricted the maximum permissible vehicle speed limit to 55 miles per hour (mph) on all interstate roads in the United States.[1] The law was a response to the 1973 oil embargo, and its intent was to reduce fuel consumption. In the year after the National Maximum Speed Law was enacted, road fatalities declined 16.4%, from 54052 in 1973 to 45196 in 1974.[2]

In April of 1987, Congress passed the Surface Transportation and Uniform Relocation Assistance Act, which permitted states to raise the legal speed limit on rural interstates to 65 mph.[3] Under this legislation, 41 states raised their posted speed limits to 65 mph on segments of rural interstates. On November 28, 1995, Congress passed the National Highway Designation Act, which officially removed all federal speed limit controls. Since 1995, all US states have raised their posted speed limits on rural interstates; many have also raised the posted speed limits on urban interstates and noninterstate roads.

Although many factors contribute to passenger injury during a vehicle crash, the kinetic energy transferred to the vehicle occupants is the causal agent.[4] An enormous literature exists on the application of Newtonian relationships between speed, kinetic energy, and road injury and death in occupants and pedestrians.[4–6] Researchers have demonstrated that lower travel speeds and death tolls usually follow lowering of speed limits,[2,6,7] and higher travel speeds and death tolls follow increases in speed limits.[4,8–17] Data show a 17% rise in deaths following a 4% rise in speeds on US interstates.[18] Furthermore, high-speed driving on highways induces higher travel speeds on connecting interurban roads and even urban roads, producing a spillover effect that may persist over long distances and time.[19,20] Yet some still express doubts about—or ignore—the effect of increased speed limits on vehicle passenger safety.[21–23]

Previous analyses on the effect of raised speed limits in the United States following the repeal of the National Maximum Speed Law in 1995 were restricted to short postintervention periods and a limited number of states.[18,24,25] These studies did not tell us whether the effects of increased speed limits on fatalities and injuries across the entire US road system persisted years after the policy change. We evaluated the long-term impact of repealing the National Maximum Speed Limit on fatalities and on injuries in fatal crashes through the end of 2005 and across the US road system.

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