Raise the speed limit? Not so fast.

Cutting down on congestion and improving traffic flow is as easy as raising the speed limit, right? Dead wrong: New crash tests by the AAA Foundation for Traffic Safety, the Insurance Institute for Highway Safety (IIHS) and Humanetics have found that cars just can't protect drivers well enough to justify higher speeds. Colorado's own AAA-The Auto Club Group provided funding for the crash test research.

As it turns out, even small speed increases can have huge effects in crash outcomes. Together, the safety organizations conducted crashes at three different impact speeds: 40, 50, and 56 miles per hour. Slightly higher speeds were all it took to increase the driver's risk of severe injury or death. 

Key Findings
Three 2010 Honda CR-V EX crossovers were used in testing because they represented the average age (11.8 years) of a typical vehicle on U.S. roadways – and they earned the top rating in the IIHS moderate overlap front test.

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.  

What's worse, 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.

"It's true that cars are getting safer, to a point. But higher speed limits effectively cancel out the benefits of vehicle safety improvements, such as airbags and improved structural designs," said Skyler McKinley, director of public affairs for AAA Colorado. "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 Impact
Drivers often travel faster than posted speed limits, and so policymakers are tempted to raise limits to match travel speeds. Even then, unfortunately, people still go faster. Today, 41 states allow 70 mph or higher speeds on some roadways - including Colorado. 

It's more than just a number. In Colorado, in 2018, 33% of all fatalities and 33% of all crashes had a speed-related component. All told, across the country, a 2019 IIHS study found that rising speed limits have cost nearly 37,000 lives over 25 years.

Drivers tend to overestimate the time saved by speeding, as do policymakers when it comes to raising speed limits. A motorist would have to travel 100 miles to save roughly 5 minutes, moving at 80 mph instead of 75 mph. Speed kills and isn't worth the cost.

And, because higher speeds tend to increase the severity of and emergency resources necessary to attend to crashes, they tend to slow down traffic by creating more congestion. 

The Solution
When correctly set and enforced, speed limits improve traffic flow and maximize all public road users' safety. They should never be raised - or lowered - only to manipulate traffic volume on a particular roadway. The end goal shouldn't be expecting drivers to obey the speed limit; they won't. Rather, policymakers and engineers should consider infrastructure changes based on road type to calm traffic flow such that speed limits are followed. 

In a pinch, they should also consider proven countermeasures: high-visibility enforcement and carefully implemented speed-camera programs that consistently and equitably enforce speed limits 24/7.

"Cars are safer than they've ever been, but nobody's figured out how to make them defy the laws of physics," McKinley said. "This research underscores just how dangerous high speeds often are, and why there are speed limits in the first place. A speeding driver may arrive at their destination a few minutes faster, but is it worth the tradeoff of losing your life in a crash?"

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% 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% of new vehicles have earned a good rating when tested at the 40 mph impact speed.