's Guide to Interpreting Crash Tests and Rollover Ratings — and Why You Should Care

Even though 2003 had the lowest crash fatality rate per 100 million miles of travel on record, there were still 42,643 people killed and nearly 2.9 million people injured on U.S. roads, according to the National Highway Traffic Safety Administration. Because of this, understanding how a vehicle performs when involved in a crash is important to consider before making a purchase.

All vehicles sold in the United States must pass Federal Motor Vehicle Safety Standards in the form of 30-mph frontal and 33.5-mph side-impact compliance crash tests, but the relative safety of all vehicles above this minimum standard varies greatly.

The most important things to know about crash tests:

Not all results can be compared
Model-to-model comparisons of frontal crash ratings are valid only within a vehicle class or between models of comparable weight (within 250 pounds). The test reflects how the vehicle would fare in a collision with another of the same model, not versus a larger or smaller vehicle (or a lower- or higher-riding vehicle). A heavier vehicle would protect its occupants better than a lighter one if all other factors were equal, but they never are. So a large vehicle with a Poor rating is not necessarily safer than a small vehicle with a Good rating. Unfortunately, researchers have not yet devised a reliable method for reporting the effect of size differences on a vehicle's score.

Note: Side-impact crash tests are comparable across classes because the sled that rams the test vehicles is of a consistent size and weight. See the section titled "Side-impact ratings have deficiencies" below.

Crash tests differ by agency
The Dodge Durango performs well in the NHTSA frontal crash test, earning a double five-star rating.

The two testing agencies perform different types of frontal tests. NHTSA crashes cars head-on into a solid immovable barrier. Neither the angle nor the obstacle corresponds with the majority of real collisions. The Insurance Institute for Highway Safety conducts a frontal-offset crash into a deformable barrier that reacts like another vehicle. This gauges how well half of the vehicle's front end absorbs crash energy. Many experts say this test is more revealing and better represents the majority of real-world crashes. To see IIHS crash-test video on, click here.

Side-impact ratings have deficiencies
Side-impact crash tests currently aren't as telling as we'd like. Though NHTSA has tested more models than IIHS for side-impact protection, we dismiss these tests as inadequate and, arguably, flawed for two reasons:

  • The sled employed to "T-bone" the stationary test vehicle has the height and mass of a car, not an SUV or pickup truck. This tends to minimize its intrusion into the cabin — a best-case scenario.

  • NHTSA's chance-of-injury data are based on trauma to the test dummies' torsos, not their heads. Occupants' heads are more susceptible to injury in a side impact, and head injuries are more often serious and potentially fatal.
The sled used in IIHS side-impact crash tests is designed to simulate a collision with a truck or SUV.

The IIHS side-impact test does measure head injury and employs a sled as high and heavy as a full-size SUV or pickup, a more dangerous scenario. Unfortunately, IIHS has just begun this program and few models have been tested. Because the sled is consistent, comparisons of side-impact ratings are valid across vehicle classes.

Rollover ratings have shortcomings
Auto manufacturers and safety experts considered NHTSA's original Rollover Resistance Ratings, begun in the 2001 model year, inadequate at judging a model's rollover propensity because they were based solely on a mathematical calculation of the vehicle's center of gravity. For the 2004 model year, NHTSA has combined this calculation with a "fishhook" dynamic driving test in which the test vehicle swerves suddenly and then overcorrects. The combined results, called simply NHTSA Rollover Ratings, give a percentage chance of rollover — a star rating based on this chance and whether or not the model tipped up on two wheels during the fishhook test. These new ratings are a step in the right direction, though some automakers still criticize them for extrapolating some conclusions.

Some models are not rated
If the model you seek is missing, results may be pending or the vehicle may not be eligible. Both agencies concentrate on the highest-volume vehicles. Convertibles are rarely tested for this reason. Results for new or recently reengineered models are likely to appear months after the vehicle goes on sale because both agencies purchase their test subjects from dealerships, just as consumers do. NHTSA tends to note if a vehicle is TBT (to be tested) or if results are pending or under review. IIHS gives no clue as to future reports.

Crash Tests