Speed limits are higher on many U.S. roads than they used to be, and motorists are going faster — in many cases a lot faster than the newly posted limits. There's a notable absence of public support for, or political will to, lower speed limits, or even to enforce existing limits in the interest of public safety.
"The perception is that moderate speeding is a harmless infraction, not a serious safety hazard," Institute chief scientist Allan Williams says. "And for any individual motorist on any given trip, this perception is probably accurate. Getting a ticket for speeding, let alone getting into a crash or being injured, isn't likely to happen. But this doesn't mean speeding is harmless. There's a significant societal cost in the form of an increase in crash deaths and injuries."
For years, Institute and other research has quantified the price in lives we pay to get from here to there a little bit faster. The most recent estimate is that higher speed limits increase deaths on rural interstates by about 35 percent. This is the main finding of a new study of fatalities in states where speed limits on rural interstate highways were raised to 70 or 75 mph during 1995-96. Previous studies, including Institute research, also show increased fatalities associated with higher speed limits (see "Deaths go up on interstate highways where higher speed limits are posted," Jan. 16, 1999).
Researchers at the Land Transport Safety Authority of New Zealand examined the number of deaths per million vehicle miles driven in U.S. states that raised speed limits on rural interstates and in states that retained prior limits following the repeal in November 1995 of the national maximum speed limit. The researchers grouped states according to their speed limits — 75 mph, 70 mph, and states where speed limits on rural interstates remained at 65 mph. Excluded from the study were 16 states where there aren't any rural interstates or where speed limits were changed outside of the 1995-96 timeframe. Texas was excluded because the nighttime speed limit differs from the daytime limit.
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.
Geographical differences among the states that changed or didn't change their speed limits may have contributed to the estimated effects. All states that raised speed limits to 75 mph were in the western United States, while most that didn't change were northeastern and midwestern states.
"Whenever vehicle speeds increase, death rates also increase," says Institute chief scientist Allan Williams. "And the reverse is true. In 1974 when the national maximum speed limit lowered the limits across the country to 55 mph, fatality rates dropped significantly."