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Understanding Side-Impact Crash Tests

Understanding Side-Impact Crash Tests

By Jeff Youngs, February 24, 2012
Though front-impact collisions carry the greatest risk of injury to vehicle occupants, side impacts also involve a high risk for injury. Therefore, side-impact crash-test ratings are an important factor when choosing an automobile. While the side-impact tests from both the National Highway Traffic Safety Administration (NHTSA, and the Insurance Institute for Highway Safety (IIHS, simulate a collision that might occur in an intersection, the tests are conducted differently by each organization and thus the results often vary. While ratings from both groups are valuable, each test is a separate measure of various safety factors of the vehicle you might be considering.

The NHTSA test
NHTSA uses two crash-test dummies that represent average-sized men, what the industry calls a "50 percentile male," meaning that roughly half the adult male population is bigger and half is smaller. These dummies are 5 feet 7 inches tall and weigh 170 pounds. One dummy is placed in the driver's seat, while the other is seated in the rear of the vehicle, directly behind the driver. A 3,015-lb. barrier on a sled is then slammed into the driver's side of the vehicle at 38.5 mph.

The force of the impact on the dummy's head, neck, chest, and pelvis is measured, but the publicly-released star ratings indicate only the chance of serious injury to the chest. Head injuries, which are not factored into the star rating, are reported separately as (what NHTSA calls) a "safety concern" if the head injury score is considered excessive. NHTSA's star ratings range from one star (26 percent or greater chance of serious injury) to five stars (5 percent or less chance of serious injury).

The IIHS test
The IIHS test uses two dummies to represent small women, and places one in the driver's seat and the other in the rear seat of the vehicle behind the driver. These dummies, which are considered the size and weight of a 12-year-old child, are 5 feet tall and weigh 110 pounds. IIHS uses these dummies rather than the average adult male dummy because research indicates that the occupants most likely to be affected by a side-impact crash are people of small stature.

In addition, the IIHS barrier has a different shape and weighs more than the one used by NHTSA, which results in a more severe side-impact crash. IIHS uses a 3,300-lb. deformable barrier that is taller and shaped like the front of a pickup or sport utility vehicle (SUV). The barrier is propelled into the side of the test vehicle at 31 mph.

IIHS measures the potential of injury to the head, neck, chest, abdomen, pelvis, and femur, and gives one comprehensive side-impact rating based on the performance in all of these areas. The group rates each vehicle using one of four scores, which range from "good" to "poor."

Interpreting the results
Because the vehicles tested by each organization are impacted by the same-size barrier at the same speed, the side-impact ratings can be compared to all other vehicles that have been tested by that organization. This means that a five-star rating for a mid-size sedan and a five-star rating for a large SUV are equal in terms of the chance of injury to the occupants.

Although side-impact ratings can be compared across vehicles of various sizes, frontal-impact tests cannot be compared across vehicles of different size. Because the object impacting the vehicle in a frontal impact is of the same size and weight as the object being tested, those ratings are not comparable between vehicles of different sizes or weights. To learn more about frontal impact tests, read "Understanding Frontal-Impact Crash Tests."

To view crash-test results from both organizations, visit NHTSA's ( or IIHS' ( Web site.
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