Even small speed increases can have huge impacts on crash outcomes and cancel the effectiveness of vehicle safety features, according to new crash tests by the AAA Foundation for Traffic Safety, the Insurance Institute for Highway Safety (IIHS) and Humanetics. The organizations partnered to study the damage from crashes at three different impact speeds (40, 50 and 56 mph). The results showed slightly higher speeds were enough to increase the driver’s risk of severe injury or death.
“Motorists often travel faster than posted speed limits. But, when officials raise limits to match those travel speeds, motorists drive even faster,” said Lori Weaver Hawkins, manager, public and government affairs, AAA Blue Grass. “When speed limits increase, the protection provided by vehicle safety features is in doubt.”
In 2020, 1,306 of crashes in Kentucky were due to the driver exceeding the speed limit, causing 944 injuries and 124 fatalities, according to Kentucky State Police data. Despite fewer vehicles on the road due to the pandemic, this represents an increase from 2019 when 1,226 crashes resulted from exceeding the speed limit, causing 831 injuries and 96 fatalities.
Speed limits trend higher
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 rising speed limits over the past 25 years have cost nearly 37,000 lives. 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.
As the crash speed increased in the tests, researchers found more structural damage and greater forces on the crash dummy’s entire body.
Vehicle safety improvements diminished
“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.”
The study found that 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 crash 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 equipped 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,” commented Jack Jensen, vice president of engineering at Humanetics.
At both 50 and 56 mph, the steering wheel’s upward movement caused the crash 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.
Four states ― North Dakota, Maryland, Indiana and South Carolina ― are currently considering measures that would increase speed limits under specific situations.
Drivers want to save time, and local transportation agencies want to improve traffic flow, but increasing speed limits to address those concerns can come at a deadly cost. 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.”
Currently, only 14 states and the District of Columbia have maximum speed limits lower than 65 mph on urban Interstate highways, according to IIHS. Only one state ― Hawaii ― has speed limits less than 65 mph on rural interstate highways.
Rather than raising and lowering speed limits to manipulate traffic volume on particular roadways, states are urged to use engineering and traffic surveys when setting maximum speed limits.
“Policymakers also need to 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,” said Jake Nelson, AAA director of traffic safety advocacy and research.
This study is the second part of the AAA Foundation for Traffic Safety research examining the effect of posted speed limit changes on safety. In the Foundation’s first study, traffic engineers were asked how posted speed limits are set and what factors they consider in changing them.
