Speed limit increases are tied to 37,000 deaths over 25 years

May 15, 2019

Rising speed limits over the past 25 years have cost nearly 37,000 lives, including more than 1900 in 2017 alone, a new study by the Insurance Institute for Highway Safety shows.

The research, an update of a 2016 analysis, calls attention to the trade-off between a few minutes of saved travel time and the increased risk of fatalities.

“About 10,000 people a year die in speed-related crashes,” IIHS President David Harkey said. “We can reduce this toll through effective, high-visibility enforcement and traffic engineering measures. Reasonable speed limits also have a crucial role to play, as our new study demonstrates.”

Maximum speed limits are set by the states, and they have been rising since the mid-1990s. Proponents of raising the speed limit often argue that such increases simply bring the law in line with reality, since most drivers exceed the limit. Once the limit is raised, however, drivers go even faster.

Today, 41 states have maximum speed limits of 70 mph or higher. Six states have 80 mph limits, and drivers in Texas can legally drive 85 mph on some roads.

For the new study, Charles Farmer, IIHS vice president for research and statistical services, analyzed the effect of changes in the maximum posted speed limit in every state from 1993 to 2017. Looking at annual traffic fatalities per mile traveled for each state and considering other factors that affect fatality rates — including changes in unemployment, the number of potential young drivers (ages 16-24) and the seat belt use rate — he calculated the effect of speed limit increases.

Farmer found that a 5 mph increase in the maximum speed limit was associated with an 8 percent increase in the fatality rate on interstates and freeways — the roads most directly affected by changes to the maximum speed limit — and a 3 percent increase on other roads. In total, over the 25-year study period, there were 36,760 more deaths — 13,638 on interstates and freeways — and 23,122 on other roads — than would have been expected if maximum speed limits hadn’t changed over that time.

Of the 37,133 people who died on U.S. roads in 2017, Farmer estimates that 1934, or 5 percent, would still be alive if speed limits hadn’t changed since 1993.

“Driving 70 instead of 65 saves a driver at best 6-and-a-half minutes on a 100-mile trip,” Farmer said. “Before raising speed limits, state lawmakers should consider whether that potential time savings is worth the additional risk to lives.”

Click here to see the data on deaths and expected deaths if maximum speed limits had not increased.