As manufacturers have sought to improve their ratings, three main strategies have emerged for improving protection in IIHS small overlap front tests: strengthening the occupant compartment, adding new structures to engage the barrier and creating an additional load path for crash forces.
IIHS researchers identified these types of structural changes in a study of 36 models evaluated since the small overlap test program began in 2012. They found that these modifications work best in combination with each other and that, because they affect dummy movement, they often necessitate changes in the restraint system as well.
The most basic change is to strengthen the occupant compartment, and on nearly every vehicle studied at least one part of the door frame was beefed up.
Extending the bumper and adding engagement structures allow some vehicles to move sideways away from the barrier after striking it. When this happens the dummy experiences less change in velocity but ends up further to the left side of the vehicle, increasing the risk that the head could miss the front airbag if the safety belts and airbags aren't modified to better control the dummy's movement.
Among the vehicles whose structures held up best were those that have reinforced side frames tied into the main frame rail, providing an additional load path. Without such measures, crash forces generally go directly into the front wheel, suspension system and firewall. Major intrusion into the occupant compartment typically results.
One common problem in the small overlap front test is that the steering column moves to the right. When this happens, the front airbag moves as well, and the dummy's head slides off the left side of the airbag. In a few of the modified vehicles, this was addressed by changes explicitly meant to limit steering column motion. In others, reduced intrusion of the door frame and instrument panel was enough to increase steering column stability.
Areas modified for small overlap performance
Not pictured: door beam, seat mount, wheel, steering column