Crash incompatibility

Crash incompatibility, crash compatibility, vehicle incompatibility, and vehicle compatibility are terms in the automobile crash testing industry. They refer to the tendency of some vehicles to inflict more damage on another vehicle (the "crash partner vehicle") in two-car crashes. Vehicle incompatibility is said to lead to more dangerous, fatal crashes, while compatibility can prevent injury in otherwise comparable crashes.

The most obvious source of crash incompatibility is mass; a high-mass vehicle such as a large MPV or SUV will tend to cause much more serious damage in a crash with a lighter vehicle such as a typical sedan or compact car. In particular, research by Michael Anderson and Maximilian Auffhammer suggests that "controlling for own-vehicle weight, being hit by a vehicle that is 1,000 pounds heavier generates a 40-50% increase in fatality risk." Incompatibility may also result from the specific shape, stiffness, or other design aspects of the impacting vehicles. For example, some SUVs and pickup trucks ride higher than cars and lack crumple zones to absorb impact energy. Another source of incompatibility is that heavier vehicles are required to have stronger front ends because of today's test requirements like the NCAP test.

The National Highway Traffic Safety Administration has done studies of the "aggressiveness" of vehicle designs. The term "aggressiveness" is used to denote the average injury risk a vehicle imposes on occupants of other vehicles during collisions. A 2003 NHTSA study estimated that in vehicle to vehicle crashes, the design of minivans was 1.16 times as aggressive as cars, pickups were 1.39 times more aggressive, and SUVs were 1.71 times more aggressive than cars. When weight was included in the analysis, light trucks (including SUVs) were estimated to be 3.3 times more aggressive than cars in head-on crashes and perhaps more so in side impact crashes.

These studies have been controversial as they affect public perception and policy decisions on CAFE standards and light truck safety test standards as they exist today. NHTSA does not define a car or a light truck based on weight (e.g., the Chrysler PT Cruiser is classified as a light truck whereas a Lexus LS 600h L, a vehicle that weighs 66% more per published specifications, is classified as a car). So while there have been no proposals to eliminate light trucks (which includes minivans, SUVs and pickups), doing so would not eliminate incompatibility because there would still be lighter vehicles crashing into heavier vehicles.

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