The recent passenger-side tests show how big the differences can be. In this group of small SUVs, most didn't perform as well when they were crashed into a barrier on the right side instead of the left. That was even true of models that appeared symmetrical after removing bumper covers and other external components.
"When structural improvements are visible only on the driver side, there are large differences in performance," Mueller says. "But the inverse is not true. Some vehicle structures look the same on both sides, but they don't perform the same. That's why we can't rely on visual analysis but need to monitor this issue and possibly begin rating vehicles for passenger-side protection."
The 2015 Toyota RAV4 and the 2014 Nissan Rogue were the only vehicles to appear asymmetrical. In the passenger-side test, the RAV4 was the worst performer. If the Institute issued ratings for passenger-side protection, the RAV4 would earn a poor rating. The Rogue would earn a marginal.
These two vehicles had the highest amount of passenger-side intrusion. Intrusion measures are important because they indicate how well the structure held up; the greater the amount of intrusion, the higher the likelihood of serious injuries.
Maximum intrusion in the passenger-side test was 13 inches more than in the driver-side test for the RAV4 and 10 inches more for the Rogue. The Rogue's door hinge pillar was torn off completely, and the RAV4's door opened. In a real crash, an open door would leave the occupant at risk for ejection.
Two vehicles that appeared symmetrical, the 2014 Subaru Forester and the 2015 Mazda CX-5, also had substantially more intrusion in the passenger-side test than in the driver-side test.
In earlier research, Mueller found that the most common change manufacturers make to improve vehicle structure for small overlap protection is to strengthen the occupant compartment. To do this, they might use a different type of material or add a few millimeters of thickness — changes that can't be discerned from a visual examination. It's likely these types of modifications were made to the Forester and CX-5, but only on the driver side.
The other three vehicles tested had relatively similar structural performance on both sides of the vehicle. The small differences that were observed could have been caused by normal variability in test results. Another factor is that vehicles are to a certain extent inherently asymmetrical. For example, structures to secure the steering wheel and pedals may provide additional bracing around the driver-side toepan, which prevents some intrusion.
In addition to the seven passenger-side small overlap tests, Institute engineers conducted two passenger-side moderate overlap tests to make sure there weren't any differences in performance in that type of crash. One visually symmetrical vehicle, the 2015 Honda CR-V, and one asymmetrical vehicle, the RAV4, were chosen for these tests. There was little difference from the driver-side moderate overlap tests, and both vehicles would receive a good passenger-side moderate overlap rating.
"We conducted the moderate overlap tests as a spot check, and we weren't surprised that both vehicles performed well," Mueller says. "Many of today's models are designed for the global market and are subject to driver-side moderate overlap tests in right-hand-drive countries. With small overlap, there isn't the same incentive for symmetrical design because we're the only organization conducting the test."
IIHS passenger-side small overlap ratings would remedy that situation. The Institute could start such a program next year and make it a requirement for one of its safety awards as early as 2018.
