Perception
A brand new crash take a look at metric helps us assess the chance posed by head-whipping motions throughout collisions.
By Becky Mueller
January 30, 2025
Image a boxer taking a tough punch to the face, his head whipping round shortly after his opponent’s glove makes contact.
Drivers and passengers can expertise comparable rotational head movement throughout crashes in some automobiles. And simply as with an individual who will get punched within the face, that head-whipping motion could cause concussions and different mind accidents that aren’t instantly seen.
Up till now, we haven’t had a great way to evaluate the chance of rotational mind harm as a part of our crash exams. However due to a metric first adopted by the NFL for helmet evaluations, that’s set to vary. We’re at the moment laying the groundwork to combine this metric into our crash take a look at standards in order that our scores will present a fuller image of harm threat. This in flip will set the stage for airbag enhancements that may cut back the chance of a majority of these accidents.
On the entire, trendy automobiles do a wonderful job of defending automobile occupants’ heads. In a frontal crash, for instance, the frontal airbag will cushion an individual’s head because it strikes ahead, stopping contact with any exhausting surfaces. That’s often the top of the story, however sometimes the pinnacle will whip to the facet after putting the airbag exhausting. We’ve seen this occur to the dummy in our crash exams; in the true world, whereas comparatively rare, we see proof of it in post-crash concussions and different accidents.
To know how we plan to measure this threat — and why we weren’t in a position to do it earlier than — you first want to know a bit about crash take a look at dummies. Dummies are designed to be sturdy sufficient to face up to tons of of high-speed crash exams. In contrast to human bones, a dummy’s steel skeleton doesn’t simply break. For that reason, we depend on measurements recorded by sensors within the dummy to inform us how a human physique would reply.
Present crash take a look at dummies may be instrumented with as much as 200 sensors within the head, torso, legs and arms, offering engineers with a wealth of details about what the dummy experiences throughout a crash. These measurements can inform us what sort of accidents can be potential or seemingly for a human in an similar crash. We use that data, mixed with an evaluation of the construction surrounding the occupants and observations of the motion of the dummy in the course of the crash, to assign a score based mostly on crash take a look at efficiency.
Deciphering the measurements recorded by dummies depends on many years of harm biomechanics analysis. Some accidents may be characterised by a easy measure — for instance, 1,400 kilos of mixed pelvic pressure equates to a forty five% threat of pelvic fracture. In eventualities through which mixtures of forces, accelerations or rotations contribute to harm, a mathematical components is used to interpret the contributing parts.
Automobile scores utilizing our present harm standards have been validated by real-world crash knowledge. Folks in automobiles with good scores are much less prone to die in crashes than in comparable collisions in poor-rated automobiles. The factors have additionally helped automakers design safer automobiles. For instance, they helped deliver concerning the integration of airbags into automobiles, which have saved greater than 70,000 lives.
Amongst these metrics, the one we now have at all times used for head harm is named merely the pinnacle harm criterion, or HIC. HIC measures the period of head accelerations and was developed to evaluate the chance of cranium fractures from exhausting impacts in opposition to automobile interiors. In different phrases, it measures linear impacts, however doesn’t seize high-speed rotations like the type I described above.
In 2012, IIHS added rotational movement sensors to our dummy fleet and commenced investigating methods to interpret the information they collected. The primary accessible metric was the mind harm criterion, or BrIC, a components developed by the Nationwide Freeway Site visitors Security Administration. My colleagues and I calculated BrIC for 150 IIHS small overlap entrance and reasonable overlap entrance crashes however found the formula struggled to establish complicated head motions noticed in the course of the exams. The place it did establish harm dangers, it was typically unclear how the airbag efficiency could possibly be improved. We determined to attend for different standards that will higher match our crash take a look at eventualities.
A greater possibility quickly got here alongside within the type of the Diffuse Axonal Multi-Axis Common Analysis (DAMAGE). This rotational head harm metric developed by the College of Virginia is utilized in mixture with HIC to evaluate helmet efficiency within the NFL. It has additionally been utilized by the European New Automotive Evaluation Program for its crash take a look at scores since 2022. We determined to take it for a take a look at drive.
The unique DAMAGE components was based mostly on the mind of a mean man, which works with the fiftieth percentile male dummies we use. Nevertheless, we additionally use fifth percentile feminine dummies in our crash exams, so we funded analysis that recalculated the mind pressure tolerances for a small girl.
Making use of DAMAGE to our crash exams, we discovered it was higher than BrIC at measuring the impact of successive actions — for instance, a head hitting an airbag, sliding off after which hitting the dashboard and rotating throughout rebound. Whereas BrIC would deal with these occasions as in the event that they occurred concurrently, DAMAGE elements within the timeline and due to this fact doesn’t overstate their results.
We’ve calculated DAMAGE scores for about 800 dummies in entrance and facet exams. As anticipated, for almost all of dummies, DAMAGE, HIC, and our visible assessments of dummy motion all indicated the dummy’s head was well-protected in the course of the crash. However for about 60 dummies, DAMAGE gave us new perception into doubtlessly dangerous head motions that HIC didn’t seize, indicating it could possibly be a helpful complement to current analysis standards.
For automobiles through which dummies had excessive DAMAGE scores, there are possible options to scale back harm threat. For instance, one concept to scale back head rotations is a deeper frontal airbag that’s softer within the middle, the place an individual’s head would hit. This is able to create a “catcher’s mitt” impact that cradles the pinnacle as a substitute of inflicting it to deflect off the floor of the airbag and whip to the facet.
Though we aren’t prepared so as to add DAMAGE scores to our crash take a look at scores, we will probably be monitoring them. Beginning this 12 months, scores will probably be calculated for all crash exams and the outcomes recorded in our technical stories. Automobile producers don’t want to attend to begin in search of methods to forestall the head-whipping motions that DAMAGE reveals.