IS RAISING THE SPEED LIMIT WORTH THE RISK?
Drivers want to save time and local transportation agencies want to improve traffic flow, but at what cost? With posted speed limits increasing on roadways around the country, a vehicle's ability to protect drivers in crashes is in doubt.
Small speed increases can have huge effects on crash outcomes, as shown in new crash tests by the AAA Foundation for Traffic Safety, Humanetics and the Insurance Institute for Highway Safety. The safety organizations conducted crashes at three different impact speeds (40, 50 and 56 mph). They found the 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 70 mph or higher speeds on some roadways, including eight states that have maximum speeds of 80 mph or more. A 2019 IIHS study found that increasing speed limits have cost nearly 37,000 lives over 25 years. AAA and IIHS urge policymakers to factor in this danger from higher speeds when considering speed limit changes.
“We conducted these crash tests to assess the effect of speeds on drivers and learned that a small increase could make a big difference on the harm to a human body,” said Dr. David Yang, executive director of the AAA Foundation for Traffic Safety. “A speeding driver may arrive at their destination a few minutes faster, but is the tradeoff of getting severely injured or even losing one's life worth it if a crash occurs?”
The AAA Foundation collaborated with IIHS and Humanetics to examine how speed affects the likelihood and severity of occupant injury in a crash. 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. Calspan Corp. conducted all the tests in its crash laboratory in Buffalo, New York.
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,” said 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, there was minimal intrusion into the driver's space. But at the 50-mph impact speed, there was noticeable deformation of the driver side door opening, dashboard and foot area. At 56 mph, the vehicle interior was significantly compromised, with the dummy's sensors registering severe neck injuries and a likelihood of fractures to the long bones in the lower leg.
“Our crash test dummies are instrumented with hundreds of sensors to measure the injury risk so that we understand the scientific limits of safety and injury prevention. Understanding that the risk of serious and permanent injury becomes significantly higher in crashes beyond statutory speed limits clearly demonstrates why there are limits in the first place,” said Jack Jensen, vice president of engineering at Humanetics.
At both 50 and 56 mph, the steering wheel's upward movement caused the dummy's head to go through the deployed airbag. This caused the face to smash into the steering wheel. Measurements taken from the dummy showed a high risk of facial fractures and severe brain injury. When correctly set and enforced, speed limits improve traffic flow and maximize all public road users' safety.
“Cars are safer than they've ever been, but nobody's figured out how to make them defy the laws of physics,” said Harkey of IIHS. “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.”
Speed limits should not be raised or lowered only to manipulate traffic volume on a particular roadway. States are urged to use engineering and traffic surveys when setting maximum speed limits.
Policymakers need to also think beyond enforcement to control speeds and should consider infrastructure changes based on road type to calm traffic flow appropriately so that posted speed limits are followed.