US safety watchdog slams truck trailers

THE US road safety watchdog has called on the government to tighten up legislation after tests showed up a big variation in underrun protection.

The tests crashed a Chevrolet Malibu sedan into the back of eight different semitrailers in a test designed to simulate a vehicle hitting the trailer at about 60km/h.

The tests showed that when a car hit the overrun barrier - designed to stop a car from slipping underneath in the event of an accident - all performed well.

However, if the crash was offset so only part of the car’s front hit the barrier, the results were very different.

“(With) only half the width of the car overlapped with the trailer, all but one trailer passed,” the IIHS said in its report handed down yesterday.

“However, when the overlap was reduced to 30 per cent, every trailer except one ... failed.”

The institute said it used a 30 percent overlap for the most challenging underride test “because it is the minimum overlap under which a passenger vehicle occupant's head is likely to strike a trailer if an underride guard fails”.

The IIHS identified that part of the problem was the way that the underride barriers were made and fixed to the chassis of the semitrailer, leaving unsupported overhangs on each side.

The trailer that passed the test had extra strengthening to help it hold its form after a crash.

“All the improvements in occupant protection that have helped drive down crash deaths in recent decades count for little when the front of a passenger vehicle ends up under a truck,” the institute said.

“When this happens, the top of the occupant compartment gets crushed because the structures designed to absorb the energy of a crash are bypassed.

“The airbags and safety belts can't do their jobs, and people inside can experience life-threatening head and neck injuries.”

The IIHS has made a recommendation to the US government to introduce minimum underrun standards similar to its North American neighbour, Canada, after a Canadian-built semitrailer was the only one to pass the tests.

The IIHS said it is yet to hear a response from the government.