So apparently knee bags do virtually nothing to prevent injury in the event of a crash. And that news is coming from the Insurance Institute for Highway Safety, so we’re inclined to believe them.
Knee airbags. Your car probably doesn’t have them, but a few out there do. They’re marketed as a means of preventing injuries to your lower extremities (ie. your legs) by distributing the force of an impact across a nice, squishy cushion of rapidly inflated air. We know that airbags that spring forth from steering wheels, dashboards, and side windows definitely work to prevent injury, but do airbags located below the dash work to prevent leg injuries?
Nope.
That's the news from the IIHS's latest study, published last July. The institute studied crash data from real-world and laboratory conditions to determine if knee airbags actually did something to improve occupant safety.
Researchers looked at over 400 frontal crash tests using dummies to see how knee airbags affected things. Real-world data was gathered from 14 states and compared injuries reported with and without knee airbags.
The in-lab results found a small effect on injury measurements during driver-side small overlap and moderate overlap frontal crashes. In the small overlap test, chances of head injury were slightly reduced, but lower leg and right femur injury chances were slightly increased. For moderate overlap tests, the effect of knee airbags was negligible.
In the real world, researchers found knee airbags to improve your chances of avoiding injury by 0.5%, but also noted that this number “wasn’t statistically significant.” This means that 0.5% was within the study’s margin of error and could therefore be totally wrong.
“There are many different design strategies for protecting against the kind of leg and foot injuries that knee airbags are meant to address,” says Becky Mueller, an IIHS senior research engineer and co-author of the paper. “Other options may be just as, if not more, effective.”
Some of those options include structural strengthening of chassis near where the driver’s legs are located, or just moving the car’s suspension slightly. One thing seems clear: don’t base your car decision on the presence or absence of knee airbags. They don’t seem to do much.