Originally Posted by IIHS
According to the National Highway Traffic Safety Administration (NHTSA), speeding is one of the most prevalent reported factors associated with crashes. Speeding is a factor in 31 percent of all fatal crashes, killing an average of 1,000 Americans every month. In 2002, more than 13,000 people died in speed-related crashes. NHTSA estimates the economic cost to society of speed-related crashes to be more than $40 billion each year.
Isn't speed variation -- not speeding -- the real problem? No. Although research conducted in the 1950s on two-lane rural roads did indicate that vehicles traveling much faster or much slower than average were more likely to be involved in crashes, this issue is not relevant on today's high-speed highways with controlled access.6 The author of this early study acknowledged that the findings could not be extended to controlled access freeways, but some proponents of higher travel speeds have attempted to do so. Many differences in travel speeds are unavoidable because of the slower speeds of turning or merging vehicles. Many crashes, and nearly half of those resulting in occupant deaths, are single-vehicle impacts in which differences among vehicle speeds play no role or only a very minor one. Finally, the risk of death and severe injury is a direct exponential function of speed, not speed differences.
Congress responded to the oil shortage of 1973 by directing the U.S. Department of Transportation to withhold highway funding from states that did not adopt a maximum speed limit of 55 mph. The National Research Council attributed 4,000 fewer fatalities to the decreased speeds in 1974, compared with 1973, and estimated that returning the speed limit on rural portions of the interstate highway system to pre-1974 levels would result in 500 more fatalities annually, a 20-25 percent increase on these highways
6. Does the speed limit matter? Don't drivers speed anyway? Many drivers tend to drive somewhat faster than posted speed limits, no matter what the limits are. Although people often opt to travel somewhat faster than the posted limit, they do not completely ignore it but choose a speed they perceive as unlikely to result in a ticket. The more important speed-related safety issue on freeways involves the proportion of vehicles traveling at very high speeds, not the proportion violating the speed limit. The Institute's frequent monitoring of free-flowing travel speeds on interstate highways posted at 55 mph and speeds on roads with 65 and 75 mph limits shows that, in general, higher speed limits lead to greater proportions of cars traveling at very high speeds.
For example, in New Mexico, which raised its limits to 65 mph on rural interstates in 1987, the proportion of motorists exceeding 70 mph grew from 5 percent shortly after speed limits were raised to 36 percent in 1993. In 1996 when speed limits were further increased to 75 mph, more than 29 percent of motorists exceeded 75 mph; by 2003, 55 percent of motorists exceeded 75 mph.8 In Maryland, which retained 55 mph limits on rural interstates until 1995, the proportion traveling faster than 70 mph remained virtually unchanged at 7 percent during 1988-93. By 1994, 12-15 percent of cars were exceeding 70. In neighboring Virginia, which switched to 65 mph limits, the percentage exceeding 70 mph went from 8 percent in 1988 to 29 percent by 1992 and 39 percent by 1994
8. What is the effect on fatalities of raising speed limits above 55 mph? Institute studies show that deaths on rural interstates increased between 25 and 30 percent when states began increasing speed limits from 55 mph to 65 mph in 1987. In 1989, about two-thirds of this increase -- 19 percent, or 400 deaths -- was attributed to increased speed, the rest to increased travel.
A 1999 Institute study of the effects of the 1995 repeal of the national maximum speed limit indicates this trend continues. Researchers compared the numbers of motor vehicle occupant deaths in 24 states that raised speed limits during late 1995 and 1996 with corresponding fatality counts in the 6 years before the speed limits were changed, as well as fatality counts from 7 states that didn't change speed limits. The Institute estimates a 15 percent increase in fatalities on interstates and freeways.
A separate study was conducted by researchers at the Land Transport Safety Authority of New Zealand to evaluate effects of increasing speed limits from 65 mph to either 70 or 75 mph. States that increased speed limits to 75 mph experienced 38 percent more deaths per million vehicle miles than expected, based on deaths in the states that didn't change their speed limits -- an estimated 780 more deaths. States that increased speed limits to 70 mph experienced a 35 percent increase, resulting in approximately 1,100 more deaths.
