Is Raising the Speed Limit Worth the Risk?

New AAA and IIHS crash tests reveal that modest speed increases can have deadly consequences.
Andrew Gross, AAA

Drivers want to save time, and local transportation agencies want to improve traffic flow, but at what cost? With speed limits increasing on roadways around the country, the risk of getting into a more serious car crash has continued to climb.

Higher Speeds Increase Driver's Risk of Injury or Death

A small increase in speed can have a huge effect on the outcome of a crash, as shown in new crash tests by the AAA Foundation for Traffic Safety, the Insurance Institute for Highway Safety (IIHS) and Humanetics. The safety organizations conducted crash tests at three different impact speeds and found that slightly higher speeds were enough to increase the driver’s risk of severe injury or death.

Drivers often travel faster than posted speed limits, but when officials raise limits to match travel speeds, people still go faster. Today, 41 states allow speeds of 70 mph or higher, including eight that allow speeds of 80 mph or more. A 2019 IIHS study found that rising speed limits have cost nearly 37,000 lives over 25 years.

The AAA Foundation collaborated with IIHS and Humanetics to examine how speed affects the likelihood and severity of occupant injury in a crash, using test dummies. Three 2010 Honda CR-V EX crossovers were used because they represented the average age (11.8 years) of a typical vehicle on U.S. roadways and earned the top rating in the IIHS moderate overlap front test.

As the crash speed increased in the tests, researchers found more structural damage and greater forces on the dummy’s entire body.

“Higher speed limits cancel out the benefits of vehicle safety improvements like airbags and improved structural designs,” says Dr. David Harkey, IIHS president. “The faster a driver is going before a crash, the less likely it is that they’ll be able to get down to a survivable speed even if they have a chance to brake before impact.”

At the 40 mph impact speed, the tests showed minimal intrusion into the driver’s space. But at 50 mph, there was noticeable deformation of the driver’s side door opening, dashboard and foot area. At both 50 and 56 mph, the dummy’s head went through the deployed airbag, smashing into the steering wheel. At 56 mph, the vehicle interior was significantly compromised, with the dummy’s sensors registering severe neck injuries and a likelihood of lower leg fractures.“

Cars are safer than they’ve ever been, but nobody has figured out how to make them defy the laws of physics,” says Harkey. “Rather than raising speed limits, states should vigorously enforce the limits they have. This includes using proven countermeasures like high-visibility enforcement and carefully implemented speed-camera programs to consistently and equitably enforce speed limits 24/7.”

States are also urged to use engineering and traffic surveys when setting speed limits. Jake Nelson, AAA director of traffic safety advocacy and research, says “Policymakers need to think beyond enforcement to control speeds and should consider infrastructure changes to calm traffic flow appropriately so that posted speed limits are followed.”


ABOUT THE RESEARCH TESTING: The research tests were conducted following the same protocol that is used for the IIHS moderate overlap evaluation; only the speed was varied. With a test dummy representing an average-sized male in the driver’s seat, the cars were crashed with 40 percent of the vehicle's front on the driver side overlapping the barrier.

IIHS has been conducting this type of test, which simulates a head-on, partial-overlap impact between two vehicles of the same weight and size traveling at the same speed, since 1995. Since 2013, 100 percent of new vehicles have earned a good rating when tested at the 40 mph impact speed.

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