Crash incompatibility

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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. Another incompatibility may be in the specific shape, stiffness, or other design aspects of the impacting vehicles. For example, some SUVs and pickup trucks ride higher than cars. 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 [1].

The National Highway Traffic Safety Administration have done studies of the aggressiveness of vehicle designs. The term 'aggressiveness' is used to denote the injury risk to the driver of the smaller vehicle as compared to the injury risk to the driver of the larger vehicle. A 2003 NHTSA study estimated that in vehicle to vehicle crashes, minivans were 1.16 times as aggressive as cars, pickups are 1.39 times more, and SUVs are 1.71 times more aggressive than cars. When weight is 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 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. Besides, the numbers above are difficult to translate into any meaningful steps because the NHTSA does not define a car or a light truck very well (the PT Cruiser is classifed as a light truck whereas as Lexus LS430, a much heavier vehicle, is classified as a car). So, it would not make sense to say that eliminating all light trucks (which includes minivans, SUVs and pickups) will eliminate incompatibility because there would still be smaller vehicles crashing into larger vehicles. This is the case in Japan which has few light trucks but crash incompatibility is considered to be a major issue.

There have been extensive research and testing done by NHTSA, other governments,research organizations as well as the automobile manufacturers to find solutions that improve safety in the small car in collisions with a larger vehicle. In the US, a group of experts proposed major steps to improve compatibility [2]and these have been accepted as a voluntary regulation by the US automotive manufacturers as well as by most other companies selling vehicles in the US. The Canadian Government has also accepted these recommendations. This requires all manufacturers to put head protection airbags ('curtain' airbags) in all their cars within a couple of years and also to design the front end of all light trucks to be less aggressive.

Although much of the crash incompatibility debate in recent years has centered around SUVs, the concept has been around far longer. When subcompact cars were introduced in the 1970s, there was a fear that incompatibilities of mass and design could lead to more serious injuries for drivers of these smaller, lighter vehicles. Crash incompatibility is an area of active study.