IIHS study finds safety flaws in tractor-trailer trucks

You don't have to be a physicist to know that accidents involving tractor-trailer trucks are very risky for smaller vehicles. Now a new study finds that a key safety feature on the back of big rigs can make these crashes even more dangerous.

The Insurance Institute for Highway Safety (IIHS) has found that the under-ride steel guards on the back of trailers that are supposed to prevent smaller vehicles from sliding underneath often buckle or break, and that even those which meet federal safety standards can fail in low-speed crashes.

The IIHS is now petitioning the National Highway Traffic Safety Administration (NHTSA) to require stronger under-ride guards and mandate guards for more large trucks and trailers. The latest NHTSA rules, which took effect in 1998, required lower and wider guards on new trailers, but the regulation does not apply to many of the heavy trucks used every day on the nation's roads.

Seventy percent of the 3,163 people who died in crashes in 2009 involving large trucks were occupants of passenger vehicles. Under-ride, which NHTSA estimates kills over 400 people each year and injures over 5,000, is the result of the smaller vehicle's passenger compartment getting crushed beneath the trailer. Even modern vehicles, which are designed to perform well in front crashes, are not designed for such a scenario.

To assess the problem, the Institute conducted six crash tests evaluating three semi-trailer rear guards that comply with U.S. safety standards, two of which also comply with stricter Canadian standards. They used a 2010 Chevrolet Malibu—a Top Safety Pick for crashworthiness--and crashed the vehicle into the rear of the parked trailers. In three of the tests, the dummies' heads made contact with the car's hood or trailer, which could cause decapitation in a real-world situation. (See videos of the tests.)

Based on this latest IIHS study, Consumers Union feels the issue of tractor-trailer bumper compatibility with passenger cars warrants investigation by NHTSA.