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Crash Test Ratings: What's the Difference Between IIHS and NHTSA?

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author photo by Doug DeMuro April 2014

If you're a safety-conscious car shopper, you've probably checked out crash test ratings on all the vehicles that you're considering. But with two groups -- the Insurance Institute for Highway Safety (IIHS) and the National Highway Traffic Safety Administration (NHTSA) -- performing different tests, how do you know which ones to look at? We explain the differences.

NHTSA vs. IIHS

There are several differences between IIHS and NHTSA, the largest of which is that NHTSA is a federal government organization, while IIHS is a nonprofit group funded by insurance companies. Of course, this has little impact on the groups' ability to test cars: Both carry out thorough tests on several aspects of vehicle safety, but they do come up with their scores using different tests and rating systems.

NHTSA Ratings and Tests

NHTSA's crash test ratings use a star system, where a single star suggests a poor crash test performance and five stars is an excellent rating that indicates outstanding performance. The exact meaning of a star rating depends on the test. For instance, in the rollover test, five stars indicates a low likelihood of rollover, while five stars in the side-impact test indicates a low likelihood of serious injury.

NHTSA's rating system involves three tests. The first is a frontal test that measures the likelihood for driver or passenger injury when a vehicle crashes into a fixed barrier at 35 miles per hour. Next up is a side-impact assessment, which requires the averaging of a car's performance over two tests. In the first one, the car being evaluated is hit from the side by a 3,000-lb vehicle traveling at 38.5 mph. NHTSA then measures the likelihood of injury for front and rear passengers. The second component of the side-impact test measures a driver's chance of injury in a 20-mph side-impact collision with a pole.

Finally, NHTSA's last test is a rollover rating. Interestingly, this isn't a test at all but rather a mathematical formula that takes into account a car's width and center of gravity. While NHTSA doesn't actually test vehicles for rollover risk, the agency maintains that this test is valid after comparisons with statistics from actual car crashes.

Once NHTSA has conducted all three tests -- the front-impact and both side-impact tests -- and added up the numbers for the rollover assessment, an overall score is given, again on a 1- to 5-star scale. This indicates the car's overall crashworthiness.

IIHS Ratings and Tests

IIHS conducts its crash tests a little differently. For one, there's no star system. Instead, the agency ranks vehicles in one of four ways: Poor, Marginal, Acceptable and Good, with Good being the highest possible rating.

IIHS puts vehicles through five different crash tests. There's a small-overlap front test, where 25 percent of the car's frontal width strikes a barrier at 40 mph. There's a moderate-overlap front test, where a larger portion of the car strikes the barrier. There's a side test, where an SUV-like barrier hits cars at 31 mph. There's a roof-strength test, where a metal plate is pushed against a car's roof to determine whether it would easily collapse in a rollover, and there's a head-restraints-and-seats test, which measures forces on a driver's head and neck in a collision. IIHS has also recently started testing front-crash-prevention safety equipment, such as systems that avoid or alert drivers to an impending forward collision.

Depending on a vehicle's performance in IIHS tests, it can be given one of two awards. Cars that perform well are awarded a Top Safety Pick designation, indicating performance that's well above average in their class. Cars that do an outstanding job are given an even more prestigious Top Safety Pick+ award, which is one step above a simple Top Safety Pick designation.

Which to Consider?

When it comes to crash tests, you can never be too careful. So, if you're wondering which tests are most important, our advice is simple: Look at all of them. A car that aces both IIHS and NHTSA tests will surely be a good pick, while one that earns a more moderate score might not be the best choice if safety is your top concern. Either way, now you have all the facts about how IIHS and NHTSA conduct their crash tests, so you can make the most informed decision possible.

This image is a stock photo and is not an exact representation of any vehicle offered for sale. Advertised vehicles of this model may have styling, trim levels, colors and optional equipment that differ from the stock photo.
Crash Test Ratings: What's the Difference Between IIHS and NHTSA? - Autotrader