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Baby, You Can Crash My CarHow automotive safety tests work.

By Daniel Engber
Posted Monday, Aug. 7, 2006, at 6:08 PM ET

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The Toyota Camry and Toyota Rav4 performed very well in crash-test results released Aug. 6. According to the Insurance Institute for Highway Safety, the Toyotas received "Good" ratings for both front and side collisions. Meanwhile, the side-airbag-equipped Dodge Caliber scored only "Marginal" marks for side-impact protection. How do these crash tests work?

They ram the cars into barriers, and vice-versa. Both the Insurance Institute and the National Highway Traffic Safety Administration use front- and side-impact tests to rate new cars. For the front crash, the vehicles are propelled into fixed barriers that are designed to crumple the way the front of a real car might. For the side crash, the car stands still while a crushable barrier is propelled into its side.

Testers at the Insurance Institute buy two cars of a given model from dealer lots. They then drain the electrolyte from the batteries and replace the gasoline in the tanks and fuel lines with a testing solution that poses less risk of catching fire. At the end of a simulated crash, they can measure the risk of a fire in real-world conditions by checking how much of the fake gas spilled out of the car.

Dummies are carefully positioned inside the cars before each test. The standard front-crash test dummy is called the "Hybrid III biofidelic anthropomorphic test device," or just the Hybrid III. Developed by General Motors in the late 1970s, the Hybrid III consists of a steel skeleton covered in vinyl and studded with force and acceleration sensors. The head attaches to the trunk with a characteristic segmented metal neck. (Other dummy models are specialized for side-crash evaluations.)

Testers can coat the head and knees of the dummies with greasepaint to see where they make contact with the car. (After the crash, they check the car's interior for smudges.) During the test, sensors in the dummy record several-dozen measurements related to the forces exerted on its head, neck, chest, and lower extremities. Each of these measurements can be compared to "injury assessment reference values" to determine the chance that it would cause a serious injury to a real person. The government assigns its safety ratings on the basis of these probabilities. For example, a vehicle gets five stars for the front-crash if the dummies reveal less than an 11 percent chance of serious injury from the collision.

The Insurance Institute compares the dummy results with measurements of the structural damage to the car. Before the testers smash the car, they carefully document it with still photos. They also record the location of 14 landmarks, including the steering wheel, the driver's seat, and the brake pedal. By remeasuring those landmarks after the crash, they can figure out how far the damage penetrated into the interior of the vehicle.

Got a question about today's news? Ask the Explainer.

Explainer thanks Russ Rader and David Zuby of the Insurance Institute for Highway Safety.

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Daniel Engber is an associate editor at Slate. He can be reached at .
Photograph of crash test dummy on Slate's home page by Brad Granzow/AFP/Getty Images.
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