We’ve come a long way from the simple driver airbag. These days, a typical C-segment hatchback will typically have around seven fitted as standard, with some vehicles sporting eight or more.
However, it turns out one type - knee airbags - don’t do a whole lot. A study by the US Insurance Institute for Highway Safety (IIHS) concluded that the knee airbag “has a negligible effect on injury risk and may even increase it in some cases”.
The IIHS examined injury measurements from over 400 of its front crash tests, along with real-world data. Crash reports across 14 different US states were amassed to compare the injury risk in cars with knee airbags versus vehicles without.
The IIHS found that in small overlap front and moderate overlap front crash test, knee airbags only yielded a “small effect on injury measures” picked up by dummies. Knee airbags increased lower leg and right femur injury risk on small overlap tests - while giving a reduction in head injury risk - and didn’t have any effect in moderate overlap tests.
The real-world data seems to mirror this. According to the research, knee airbags drop injury risk from 7.9 to 7.4 per cent. “This result wasn’t statistically significant,” the IIHS said.
Becky Mueller, the report’s co-author and IIHS senior search engineer, concluded: “There are many different design strategies for protecting against the kind of leg and foot injuries that knee airbags are meant to address…Other options may be just as, if not more, effective.”
Is there any point in having them, then? Well, the IIHS reckons that some manufacturers are fitting these airbags to help cars get through federally-mandated tests using dummies that aren’t wearing seatbelts. The organisation concludes that knee airbags might help those who choose not to wear a seatbelt. However, its study didn’t focus on crashes involving unbelted occupants, as “dummies are always belted in IIHS vehicle ratings tests”.