Drive Smart: Understanding Crash-Test Safety Ratings

The latest cars feature a host of new safety devices

Q: My new car has a five-star overall government safety rating. Yet I read a news item that said the car did poorly in a crash test. How can this be?

Confusing stuff, this safety-rating business. The news story probably referred to a crash test performed by the Insurance Institute for Highway Safety (IIHS), not one by the federal government’s National Highway Traffic Safety Administration (NHTSA, pronounced nit-sa). Only NHTSA scores are shown on new cars’ window stickers.

NHTSA pioneered automobile crash testing with its New Car Assessment Program of 1978. In 1996, IIHS—a nonprofit organization funded by insurance companies, including the Auto Club’s affiliated Interinsurance Exchange—established its own crash-test program. Rather than duplicate NHTSA’s tests, IIHS tests generally complement them.

NHTSA tests vehicle crashworthiness in frontal and side impacts and rollovers. IIHS also performs frontal, side, and rollover tests, but with variations on the themes. For instance, NHTSA’s frontal impact test rams the vehicle straight into a barrier, affecting the entire front of the vehicle. IIHS’ moderate overlap frontal impact test simulates two vehicles colliding at an angle, involving only 40 percent of the car’s front end. Taken together, they provide a more accurate picture of how well a vehicle’s occupants might survive a collision.

Likewise, NHTSA and IIHS conduct somewhat different side-impact tests. NHTSA’s test simulates a car T-boning another car, while the IIHS test rams a heavier, taller moving barrier—simulating a typical pickup truck or SUV—into the side of the vehicle tested. The two organizations’ roof-strength tests are similar, involving a flat plate that pushes down on the tested vehicle’s roof to simulate damage that might occur if the vehicle rolls over.

Over the years, automakers have concluded that crashworthiness sells, causing them to “teach to the test.” That is, they’ve become adept at building vehicles that ace the NHTSA and IIHS crash tests—which is a good thing. If you have any doubt about industry strides in crashworthiness, watch what happens when a ’59 Chevy Bel Air crashes head-on into a ’09 Chevy Malibu (youtube.com/watch?v=xtxd27jlZ_g). It ain’t pretty.

The two organizations have also upped the ante. For 2011, NHTSA added a new side-impact test that simulates a car skidding into a light pole or a tree, crushing the driver’s door. And an IIHS small overlap frontal crash test added in 2012 garnered news headlines and caused more than a few auto execs to reach for antacid tablets. It focuses impact only on 25 percent of a vehicle’s front end (driver’s side), simulating a vehicle hitting another vehicle, a pole, or a tree head-on. According to IIHS, about 25 percent of fatalities and serious injuries occur in crashes like the one simulated by this test.

In the first batch of vehicles tested—11 luxury cars—only two, a Volvo and an Acura, earned the IIHS top rating of “good.” Eight others, including a BMW and a Mercedes, botched the test with “marginal” or “poor” ratings. Other carmakers’ vehicles didn’t fare much better. Subsequent results released in August 2013 showed that just half of the 12 small cars tested earned a “good” or “acceptable” rating.

Should you avoid a car that doesn’t ace the new IIHS test? Not necessarily. For example, IIHS doesn’t condemn a vehicle based on a single type of test. It can still earn the institute’s Top Safety Pick+ award if it receives a “good” rating in four of the five tests and no less than an “acceptable” in the fifth.

The takeaway: In making a judgment, consider all the tests from both NHTSA and IIHS. Few vehicles ace all of them—although over time, more and more will as automakers continue to improve their vehicles’ crashworthiness. To see crash-test results, go to safercar.gov and iihs.org.

Photo (top): Thinkstock

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