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Every car commercial tells you that their car has a five-star safety rating. Does this score really mean anything? What tests are being performed and who does the measuring?

The Organizations

In the United States, there are two organizations that score cars on safety ratings, the National Highway Traffic Safety Administration (NHTSA) and the Insurance Institute for Highway Safety (IIHS). The NHTSA is run by the Department of Transportation and is sometimes called the New Car Assessment Program (NCAP) or the government five star rating.

Frontal Collision Ratings

The NHTSA gets its data by running a car directly into a wall at 35 mph. The IIHS does a different test, where the impact is offset, and not directly in the middle. The IIHS test does a better job of mimicking real-life accidents. While most cars do well in directly head-on collisions, most real-life collisions are offset.

The NHTSA scores with five stars. Five stars means that there is ten percent or less chance of injury. Injury is defined as something life-threatening or for which you will need immediate hospitalization. Four stars is between eleven and twenty percent chance of injury. Three stars is between twenty-one and thirty-five percent chance.

The IIHS score is not in a five star format. They rate a vehicle as Good, Acceptable, Marginal, or Poor.

The NHTSA and the IIHS scores should be looked at in conjunction with one another. Remember, both these scores only rate what would happen if you collide with another vehicle the same size as yours. However, many crashes involve only one-vehicle, so these tests are useful.

Side-Impact Ratings

Again, the NHTSA and IIHS uses different side-impact tests. The NTSA crashes a giant beam into the side of a car and measures the shock on two male-sized dummies. They then make a star rating based on the chance of chest injury to the dummies. Five stars means less than 5% chance of injury, four stars is 6%-10%, and 3 stars is 11%-20%. They don't gage the damage to the head in this star rating, but if they think that it is excessively dangerous, they will add a safety note to their report.

The IIHS uses dummies that represent adolescents or small-statured women. This helps assess the safety of people other than men in the car. They also use a larger beam. They score their rating based on injury to the head, neck, chest, abdomen, pelvis, and femur. This is arguably a more comprehensive test than the NHTSA test.

Rollover Ratings

The NHTSA is the only company that does Rollover ratings. Rollovers are often the most fatal type of accident. The NHTSA measures the chance of a car rolling with no external catalyst, and the chance of it happening for a reason (hitting a shallow ditch, hitting the curb, going onto the shoulder). 95% of rollovers are "tripped," and have some external element.

Recent NHTSA testing has proven what we know about SUVs being much more likely to rollover than sedans or other cars.

Low-Impact Bumper Test

The IIHS performs a low-impact bumper test to see how much repairs would cost you if you gently hit something by accident. They rate the cars accordingly. Although this is not necessarily a safety rating, it will tell you what you can expect for possible repairs for your car and is something to keep in mind while purchasing a car.

When you shop

Considering the safety ratings of cars is important. But it is also important to know how these ratings are measured so that you can make the most informed decision about your purchase. Maybe you want your car to be cool, or to be functional, but most of all you want it to be safe.