Only a few states- Connecticut, Hawaii, Maryland, New Jersey, New York, Pennsylvania, and Rhode Island - retain 55 mph maximum speed limits on all highways. Delaware and the District of Columbia do not have any rural interstates, and Massachusetts has fewer than 100 miles posted at 65 mph. Fifty-five keeps down the proportion of vehicles traveling at very high speeds. More vehicles travel at 70 mph and faster in states with 65 mph speed limits than in states that retained 55 mph speed limits on rural interstates, which are designed for 70 mph travel only under the most favorable conditions.
What is the effect of raising speed limits to 65 mph? Higher travel speeds and more deaths. In states where speed limits were raised to 65 mph in 1987, the higher limits are causing about 15-20 percent more deaths on rural interstates each year than otherwise would be expected. Institute studies show that, in states that raised rural interstate speed limits, about 400 lives are lost each year because of the higher limits.
How are speed limits established? Speed limits are typically set based on a roadway's design - for example, whether it is a narrow two-lane byway or a modern controlled access freeway- and whether the surrounding area is urban, suburban, or rural. It has been argued that measuring the speed distribution of a roadway and then setting the speed limit so that 85 percent of motorists would be in compliance reduces the need for enforcement and, at the same time, reduces crash risk by narrowing variation among vehicle speeds. However, numerous studies of travel speeds on rural interstate highways have shown that 85th percentile speeds increased when speed limits were raised to 65 mph and then continued increasing. Thus, the 85th percentile is not a stationary point. It is rather a moving target that increases when speed limits are raised. If speed limits are raised to meet a current 85th percentile speed, a new 85th percentile that is higher will soon result.
Others claim that, because interstate highways meet rigid design standards for sight distance and roadway geometry, they should be posted at their design speeds. The problem is that a design speed is not necessarily a safe travel speed. The American Association of State Highway and Transportation Officials defines design speed as "the maximum safe speed that can be maintained...when conditions are so favorable that the design features govern." In other words, it is the maximum speed at which drivers can maintain a safe level of vehicle control on a particular section of highway under the conditions for which the highway was designed. Speed limits are set somewhat lower because conditions are not always favorable. Many motorists also assume there is a kind of built-in tolerance factor in speed limit enforcement, so they exceed the limit regardless of what it is.
Does research show that slightly faster speed limits would reduce crashes? No. Advocates of higher speed limits have claimed that research on speed variation indicates faster speeds are not hazardous. They cite David Solomon's research from the mid-1950s and similar studies that seem to show an increase in crash likelihood among drivers traveling slower than the average speed and a minimum of crashes at 5-10 mph above the average speed. However, the travel speeds of crash-involved drivers in these studies were obtained from driver reports and police estimates, and it is well known that drivers exceeding speed limits are likely to deliberately underestimate their speeds. Such underestimation can account for much of the apparent underinvolvement of moderately high-speed drivers in crashes. In addition, later research found that simply removing the crashes involving intersections and turning maneuvers eliminated the exaggerated overinvolvement of slower drivers in crashes. More important, the Solomon research addressed only speed variation, not speed limits. Raising speed limits raises average speeds as well.
If going faster than 65 mph is prohibited, why do vehicle speedometers go to 120 mph? There is no good reason. Although a national law enforcement summit convened by the U.S. Secretary of Transportation in 1990 called for reinstating a regulation establishing 85 mph as the top speed on speedometers in all motor vehicles, there is currently no regulation requiring it. NHTSA noted in rulemaking revoked more than 15 years ago that "speedometers that indicate speeds of 120 mph or more use more than half of the dial to indicate illegal and dangerous speeds."
In the past, automakers often promoted their products by glamorizing high speed. Although many automakers now compete in terms of safety features, there still are exceptions. For example, a television advertisement for the 1990 Nissan 300ZX Turbo - a car model with a very high crash fatality rate - featured a 150 mph race between a motorcycle, a race car, and a jet fighter plane. This ad was withdrawn in response to protest from the safety community and general public. Such ads "irresponsibly promote excessive speed and exhibit a blatant disregard for public safety," the Institute observed at the time.
Should trucks have lower speed limits than cars? Yes. Large trucks require much longer distances than cars to stop. Lower speed limits for trucks make heavy vehicle stopping distances closer to those of lighter vehicles. Slower truck speeds also allow automobile drivers to pass trucks more easily. Crashes involving large trucks not only can cause massive traffic tie-ups in congested areas, but they put other road users at great risk - 98 percent of the people killed in two-vehicle crashes involving a passenger vehicle and a large truck are occupants of the passenger vehicles.
Institute studies have shown that lower speed limits for trucks on 65 mph highways lower the proportion traveling faster than 70 mph without increasing variation among vehicle speeds. In one study, only 4 percent of large trucks exceeded 70 mph on Ohio's rural interstates with 55 mph speed limits for large trucks and 65 for cars, but up to six times the proportion of trucks exceeded 70 mph on rural interstates in three other states with uniform 65 mph speed limits. Another study found that the percentage of trucks going faster than 70 mph was twice as large in states with uniform 65 mph limits (14 percent in Arizona, 9 percent in Iowa) as it was in states with different car and truck speed limits (4 percent in California, 3 percent in Illinois).
How do speed limits and safety records in other countries stack up alongside the United States? Germany does not even have speed limits on most autobahns, for example, and longstanding claims point to the safety of these roads. Yet the death rate per 100 million vehicle miles traveled on U.S. interstate highways has generally been lower than the rate on autobahns. Fatality rates have been declining in both countries for many years, but the German rate had historically been much higher than the U.S. rate. For example, there were 1.24 deaths per 100 million vehicle miles traveled on U.S. interstate highways in 1975, compared with 2.75 deaths per 100 million miles on German autobahns. During 1984-86, U.S. and German rates were similar, but when speed limits on rural interstates were raised to 65 mph beginning in 1987, the U.S. interstate death rate became higher than the rate on the autobahn. After German reunification, autobahn fatality rates fluctuated but declined to 0.94 in 1992 while the U.S. rate reached an all-time low of 0.85.
Eighty percent of autobahns do not have speed limits, but several other factors have contributed to declining death rates on these roads. Germany has achieved a very high belt use rate - about 95 percent compared with about 50 percent in the United States. The minimum age for a drivers license in Germany is 18 years old, which eliminates a risky subset of drivers from the road. Passing on the right is illegal on autobahns, and drinking-driving laws are tougher in Germany than in the United States. All of these factors should have contributed to even lower death rates on German autobahns, but the U.S. rate has continued to decline ahead of the German rate.
Are speed-related crashes a problem on urban as well as rural roads? Yes. Speed-related fatal crashes affect all roadways, but the percentage varies by road type. According to NHTSA, about 36 percent of all fatal crashes on rural roads are related to speed, compared with about 30 percent on urban roads. Rural roads account for 40 percent of all vehicle miles traveled, but they account for 61 percent of all speed-related fatal crashes.
Are pedestrians at risk from speeding vehicles on city streets and suburban roads? Yes. The second largest category of motor vehicle deaths, after occupants, is pedestrians, and 69 percent of pedestrian deaths occur in urban areas. The speed of vehicles involved in pedestrian impacts is a major determinant of the severity and outcome of injury. There is a much higher ratio of deaths to injuries where speed limits are higher - nine times as high where the speed limit is 55 mph as on roads where it is 30 mph or lower. A federal study of pedestrian crashes found a positive correlation between speed and injury severity. In addition, vehicle speed influences the likelihood that a pedestrian will be struck in the first place because a driver cannot stop quickly enough. One study found that, even in residential zones, almost 20 percent of vehicles were traveling at more than 30 mph when they struck pedestrians. Some cities are using new approaches to slowing urban traffic to reduce pedestrian crashes, especially in school and work zones.
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