Every year the federal government and independent associations perform crash tests to evaluate vehicle safety. The results are published so consumers can have a better idea of how various year, make and model vehicles rate in terms of crash safety. The government crash tests are conducted by the National Highway Traffic Safety Institute (NHTSA). The Insurance Institute for Highway Safety (IIHS) represents insurance companies and does their own crash testing. Crash tests are also performed by the Collision Safety Institute. Others such as the Center for Auto Safety analyze the government crash test results and publish their own safety ratings that rank vehicles relative to each other.
Crash tests may be relatively simple such as a head on crash into a solid barrier at a specified speed. This type of test shows how well the vehicle structure absorbs and dissipates energy in an impact and how well the vehicle protects the driver and front seat passenger from injury. A well-designed crumple zone around the engine compartment should absorb much of a frontal impact and redirect the force around the passenger compartment to minimize injury to the vehicle occupants.
For a frontal crash test, an average-size adult male dummy is placed in the driver seat, and a smaller adult female dummy is placed in the front passenger seat. The dummies are strapped in with the factory seat belts. The vehicle is then crashed into a solid barrier at 35 mph. The dummys are then evaluated for head, neck, chest and leg injuries.
If you want to read through the NHTSA engineering test procedures for vehicle crash testing, see FMVSS 208 Crash Test Procedures and Requirements (1.6MB PDF file_).
Side impact tests ram a sled into the side of the vehicle to see how the door beams and B-pillar resist the impact, and how vulnerable the passengers are to body, head and neck injury. The NHTSA test uses a 3,015 lb. sled to ram the side of a vehicle at 38.5 mph.
A slight variation of the side impact test is a "side pole" crash test. The vehicle is angled at 75 degrees and is then pulled sideways at 20 mph into a 25cm diameter pole so the pole hits the driver's door.
The most challenging crash test is an "offset" impact into a solid barrier. NHTSA does not do this type of test but the Insurance Institute for Highway Safety does because many frontal crashes are actually offset crashes where one vehicle hits another head on but usually off-center towards the driver's side.
In an offset test, a vehicle is driven into a barrier that only crushes the front driver's side of the vehicle (a 50 percent offset). It is a more severe test because energy is concentrated on one side of the vehicle. Some vehicles that do well in a full frontal crash test do poorly in an offset crash test.
A variation of this test is the "small overlap" frontal crash test where the vehicle just clips the barrier on the driver's side (15 to 20 percent offset). Both offset tests are done at 40 mph.
The NHTSA gives vehicles a star rating after completing its crash tests. The more stars, the better. A 5-star rating is the best. A 4-star rating is Good. Other groups may assign a Good, Acceptable, Marginal or Poor rating based on a combination of the government test results and their own test results or analysis of the date.
The Center for Auto Safety publishes a report called The Car Book that rates crash test results for new vehicles. Their ratings are different from the government's simplified 5-star rating system, and take into account subtle differences in how vehicles actually perform in both front and side impacts as well as how vehicles compare to each other.
Typically, most vehicles that are tested by NHTSA receive a 4- or 5-star safety rating in the frontal crash tests, and most receive a 5-star rating in the side tests. But there are exceptions.
NHTSA crash star ratings only indicate a vehicle meets the criteria for a particular test. But two vehicles that both receive a 5-star crash rating may actually perform quite differently in a real world accident. One may be significantly safer than the other. That's why IIHS does their own crash tests to further rank and compare vehicle safety.
For example, some SUVs that receive a 5-star rating in both frontal tests and side impact tests may actually receive a Below Average rating in a Side Crash Test compared to other vehicles in the same category.
The likelihood of driver injury can also vary quite a bit between vehicles with the same star rating. Car A and Car B may both receive 5-star NHTSA ratings for the driver in the front crash test, but driver in Car A may have a 5 percent chance of receiving a life threatening injury while the driver in Car B may have a 10 percent chance of a life threatening injury. A 5 percent difference may not sound like much, but may literally mean the difference between life and death! So the more detailed information that is published regarding actual crash test results, the easier it is to pick out the best performing vehicles and the worst.
Check out the following websites for the latest vehicle safety ratings and crash test results: