Who's Doing the Rating?

Although automobile manufacturers have performed crash tests on vehicles for many years, they do so primarily as an engineering exercise in order to make improvements. Carmakers do not publish these results for public use.

Instead, consumers must turn to two groups that conduct independent testing: the National Highway Traffic Safety Administration and the Insurance Institute for Highway Safety.

NHTSA (often pronounced nit'-sah) is a division of the U.S. Department of Transportation and is perhaps the most familiar of the two agencies. NHTSA, the successor to the National Highway Safety Bureau, was established by the Highway Safety Act of 1970.

The agency is responsible for reducing deaths, injuries and economic losses resulting from motor vehicle crashes by setting and enforcing safety performance standards for motor vehicles and motor vehicle equipment. It also helps state and local governments conduct effective highway safety programs by providing grants; it can also freeze funding for states in noncompliance with federal laws.

NHTSA's frontal-impact test strikes an immovable barrier at 35 mph. This scenario doesn't mimic most real-world crashes.

NHTSA's frontal-impact test strikes an immovable barrier at 35 mph. This scenario doesn't mimic most real-world crashes.

NHTSA has multiple roles — investigating safety defects in motor vehicles, setting and enforcing fuel economy standards, and so on — but it's probably best known for its New Car Assessment Program, which performs crash tests and assigns vehicle ratings. Taxpayers fund NHTSA's crash-test program, and the agency uses tax monies to buy test vehicles and pay its staff.

Unlike NHTSA, IIHS is an industry trade group. It's comprised of major automotive U.S. insurance companies, from Alpha Insurance to Zurich North America, that fund both IIHS and the Highway Loss Data Institute, a sister organization that publishes insurance loss data on different kinds of vehicles.

According to its website, "IIHS research focuses on countermeasures aimed at all three factors in motor vehicle crashes — human, vehicular and environmental — and on interventions that can occur before, during and after crashes to reduce losses." The losses it refers to are, of course, insurance company losses in the form of claims. In 1992, IIHS opened the Vehicle Research Center, its independent crash-test facility in Virginia.

The mission of IIHS is to reduce the number and size of claims the insurance companies dole out. This clearly coincides with motorist's losses in terms of vehicles, injuries and lives. IIHS is funded by its member insurance companies, and consumers also pay through their insurance premiums to those companies.

Explaining the Ratings Scales

NHTSA uses a ratings system based on a scale from one star (the lowest) to five stars (the highest). For frontal-impact testing, both head and chest injury data are combined into a single rating and reflected by the number of stars. The rating represents a vehicle's relative level of crash protection in a head-on collision. Five stars indicate the best protection for vehicles within the same weight class. Of course, you should evaluate only the vehicles you are interested in against other vehicles within the same weight class.

NHTSA Ratings Scale
The National Highway Traffic Safety Administration uses a star-based system to characterize crash severity. The ratings show the chance of sustaining a serious injury, defined as one that requires immediate hospitalization and may be life threatening. Frontal-impact ratings combine chest and head injury data; side-impact ratings use only chest data.
RatingFrontal Impact: Likelihood of Serious InjurySide Impact: Likelihood of Serious Injury
5 stars10% or less5% or less
4 stars11% - 20%6% - 10%
3 stars21% - 35%11% - 20%
2 stars36% - 45%21% - 25%
1 star46% and greater26% and greater

Source: NHTSA

NHTSA's side-impact ratings utilize the same five-star system, but only chest injury data is taken into account. Because the sled in these tests does not replicate being hit by a higher-riding vehicle, such as a sport utility vehicle or pickup truck, we believe these ratings are somewhat deficient.

IIHS's frontal-impact test strikes an offset barrier at 40 mph. This test gives a better indication of how a vehicle will absorb crash energy in realistic collisions.

IIHS's frontal-impact test strikes an offset barrier at 40 mph. This test gives a better indication of how a vehicle will absorb crash energy in realistic collisions.

IIHS employs a slightly different rating system that uses letters and colors. The four categories are Good (green), Acceptable (yellow), Marginal (orange) and Poor (red). In some cases, IIHS will give a vehicle a Best Pick.

The criteria used to give a vehicle a certain score is based on an overall evaluation of these factors: how well the front end absorbed the crash energy and the amount of intrusion allowed by the safety cage; the injury potential to the head, neck, chest, legs and feet; and the ability of the restraints (seat belts, airbags and head restraints) to limit movement that could cause greater injury. Other factors also considered include the positioning of the head restraints to reduce whiplash and the amount of damage endured by the bumpers.

In addition to frontal- and side-impact testing, IIHS also publishes bumper and rear-impact test ratings. IIHS conducts four tests on bumpers that include: front and rear full-width impacts at 6 mph and front- and rear-corner impacts at 3 mph. These tests measure how well bumpers protect car bodies from damage in similar accident — the damage is monetized so consumers can see how pricey a small tap could be. Rear-impact tests provide data on how well head-restraint systems protect occupants against possible whiplash injury. These involve a dummy and a flat-bed sled equipped with a car seat rather than the full vehicle.

Different tests produce different results, so someone shopping for a car based on its safety rating may want to take both tests into consideration before coming to any conclusions. Even then, you must be careful to compare the similar make, model and year to get any useful information. You can't compare the ratings for a Ford Excursion SUV to a Toyota Corolla compact sedan.

© Cars.com 8/19/08
More Resources