Until now, there has not been an effective way to assess the risk of rotational brain injury in crash tests. However, thanks to a metric first adopted by the NFL for helmet evaluations, that is set to change. The Insurance Institute for Highway Safety (IIHS) is currently working to integrate this metric into its crash test criteria, aiming to provide a more comprehensive assessment of injury risk. This, in turn, could lead to airbag improvements that help reduce such injuries.
Modern vehicles generally provide excellent head protection for occupants. In frontal crashes, for example, frontal airbags cushion the head to prevent contact with hard surfaces. However, in some cases, after striking the airbag, the head may whip to the side, potentially causing injury. This phenomenon has been observed in IIHS crash tests, as well as in real-world cases of post-crash concussions.
Measuring this risk requires advanced crash test dummies equipped with sensors that can withstand high-speed impacts. Current dummies contain up to 200 sensors, providing detailed data on how the human body would respond in a crash. These measurements help determine the likelihood of injury and inform vehicle safety ratings.
IIHS has historically used the head injury criterion (HIC) to assess head injuries, focusing on linear impacts that could cause skull fractures. However, this metric does not capture high-speed rotational movements. In 2012, IIHS introduced rotational motion sensors into its dummy fleet and began evaluating new ways to interpret the data. The brain injury criterion (BrIC) was initially considered but was found to be inadequate for identifying complex head motions.
A more effective alternative emerged in the Diffuse Axonal Multi-Axis General Evaluation (DAMAGE), developed by the University of Virginia. DAMAGE, already used in NFL helmet evaluations and European crash test ratings, combines with HIC to provide a more complete assessment of head injury risk. Unlike BrIC, DAMAGE accounts for successive movements—such as a head hitting an airbag, sliding off, and striking another surface—without overstating their effects.
IIHS has applied DAMAGE to about 800 crash tests, confirming its effectiveness. While most dummies showed well-protected heads, about 60 revealed potential risks that HIC alone did not capture. For vehicles where DAMAGE scores were high, possible solutions include redesigned frontal airbags with a softer center, creating a “catcher’s mitt” effect to reduce head rotations.
Although DAMAGE is not yet part of IIHS crash test ratings, it will be monitored, with scores recorded in technical reports starting this year. Vehicle manufacturers are encouraged to explore ways to mitigate head-whipping motions and improve occupant safety before these metrics become part of formal evaluations.