A new study by the Insurance Institute for Highway Safety has found that underride guards on semi trailers are prone to failure. Despite major advances in passenger car safety since the mid-1970s, it seems the guards on tractor trailers still fail to reliably prevent vehicles from sliding under trailers in the event of a collision – a similar result to studies conducted over 30 years ago.

@funkmasterflex

Of course, some trailers are better than others, but there is no testing standard for evaluating the underride guards and their attachment points and hardware. Despite this, there is a federal safety standard for the guards, and there’s also a more stringent Canadian specification which requires the guards to be stronger and absorb more crash energy. In analyzing the Large Truck Crash Causation Study, a federal database of about 1,000 actual crashes from 2001-2003, the Institute determined that of the 115 crashes where a passenger vehicle struck the rear of a truck or semi, nearly 80 percent involved underride, and nearly half of those vehicles suffered severe or catastrophic damage.

The guards aren’t required on as many trucks as you’d first think, despite a 1996 standard calling for increased strength, guard size and energy absorbtion. Many trucks are exempt due to their trailer or chassis configuration, with dump trucks being a notable )and notably dangerous) example. When hit straight-on, the guards can perform better than offset tests, but in crash tests, the IIHS found performance was all over the map for trailer underride guards.

The worst performance in these new IIHS tests belongs to a Hyundai trailer whose guard bent and tore from its attachment points in a 35 mph crash test with a 2010 Chevrolet Malibu. Instead of keeping its passengers safe with its high-performing safety design (the Malibu is an IIHS Top Safety Pick), the front of the car slid under the trailer and left the roof structure to absorb the impact with the trailer. A Wabash trailer with a Canadian-spec guard kept the Malibu from plowing under the trailer in the 35 mph center crash test. Offset impacts – when only part of the guard is engaged by a vehicle – are still troublesome, and even the high-performing Wabash trailer suffered severe underride in a 30 percent overlap test.

In light of this ever-present danger on roadways, the Insurance Institute for Highway Safety is callig for more stringent standards, closing the gaps that allow many trucks to go without guards or use guards that don’t meet the 1996 standards for strength and energy absorption, and a more comprehensive standard that incorporates a method of better protecting vehicles in offset impacts as well as crash tests by trailer manufacturers to certify that the underride guards and their mounting systems live up to the intent of the law.