Aug. 7, 2019—A recent Insurance Institute for Highway Safety (IIHS) study found that vehicles' knee air bags have a negligible effect on injury risk and may in some cases actually increase it.

Knee air bags typically deploy from the lower dashboard and are intended to distribute impact forces to reduce leg injuries. They may also help reduce forces on an occupant's chest and abdomen by controlling lower body movement.

IIHS researchers compiled crash reports from 14 states and looked at injury measures from more than 400 frontal crash tests conducted as part of the IIHS vehicle ratings program.

Knee air bags had only a small effect on injury measures recorded by dummies in IIHS crash tests. In the small overlap test, for example, knee air bags were associated with increased injury risk for lower leg injuries and right femur injuries, though head injury risk was slightly reduced.