Background and Ratings

In recent years, cars have gotten much safer. One reason is that safety is now a selling point in new cars -- people actually seek out and buy safer cars. In the United States, the NHTSA crashes cars and analyzes data with a goal of improving car safety.

Carmakers themselves crash many vehicles each year. Car manufacturers are required to certify that their cars meet the Federal Motor Vehicle Safety Standards (FMVSS). These rules cover everything from how bright the turn signal bulbs must be to the crash-testing requirements. Carmakers have to be certain that if the NHTSA goes to any dealer in the United States, buys any car and crashes it at 30 mph, the car will pass all of the FMVSS requirements. To ensure that all of the different combinations of engines, transmissions and accessories will pass, carmakers might crash 60 to 100 vehicles themselves.

It is rare that a car fails the FMVSS requirements, so to challenge the carmakers even more -- and to provide valuable information to consumers buying cars -- the NHTSA started their New Car Assessment Program (NCAP). NCAP crashes cars at 35 mph (56 kph) in both frontal and side impact, and rates the cars based on how likely the occupants are to be injured during a crash. You can find the ratings online, a good first stop when looking for a new car.

What are my chances of being seriously injured?
This is a pretty tough question. In order to answer it, we have to define a serious injury. A lot of research has been done (and is still being done) to classify injuries. Crash-test researchers came up with a standard called the Abbreviated Injury Scale (AIS) for classifying different injuries. These same researchers published a manual that contains detailed descriptions of all the injuries normally found in car crashes. Each injury is assigned a rank based on how severe it was: 1 is just minor cuts and bruises; 3 indicates a serious injury that requires immediate medical treatment and may be life threatening; 6 is fatal.

Rating systems
Researchers have used crash test data to determine the likelihood of injuries that may be sustained in a crash. In addition, that data was used to create the NHTSA's star system. This system makes automobile safety ratings easier for consumers to understand when buying a car.

In frontal crashes, the star rating is determined by the worst score on these three criteria:

  • Head Injury Criteria (HIC)
  • Chest deceleration
  • Femur load

In order to receive a five-star rating, all three of these criteria must be below the level that indicates a 10-percent chance of severe injury. There is a star rating for each of the front seat passengers, for each type of test that was run (frontal or side impact).

Ratings for Frontal-Impact Tests
# of Stars
Result
5
 10% or lower chance of serious injury
4
 11% to 20% chance of serious injury
3
 21% to 35% chance of serious injury
2
 36% to 45% chance of serious injury
1
 46% or greater chance of serious injury

In side-impact crashes, there are two criteria:

  • Thoracic Trauma Index (TTI)
  • Lateral Pelvic Acceleration (LPA)
To achieve a five-star rating in side-impact crashes, both criteria must be in the range that indicates less than a 5-percent chance of serious injury.

Ratings for Side-Impact Tests
# of Stars
Result
5
 5% or lower chance of serious injury
4
 6% to 10% chance of serious injury
3
 11% to 20% chance of serious injury
2
 21% to 25% chance of serious injury
1
 26% or greater chance of serious injury