You may not know what a semitrailer underride guard is – but if you get into a crash with a semitrailer, it could save your life.
The Insurance Institute for Highway Safety (IIHS) is asking federal regulators to adopt tougher underride guard standards to prevent passenger vehicles from being crushed beneath semitrailers.
"The problem of underride crashes has been a longstanding danger on the road," says Russ Rader, a spokesman for the IIHS.
An underride crash occurs when a passenger vehicle rear-ends a semitrailer and ends up getting wedged beneath the larger vehicle, Rader explains. Metal bars installed at the rear of the semitrailers are designed to prevent this from happening. The problem is that the guards often fail to do their job, according to the IIHS.
"The crash tests show that some underride guards are too weak," Rader says. "Our tests show when passenger vehicles strike the outer ends of underride guards, most are too weak to prevent a passenger vehicle from sliding underneath the trailer."
The institute says other safety devices, such as air bags and seat belts, offer minimal protection to passenger vehicle occupants when cars are wedged beneath semitrailers. Typically, the tops of passenger compartments are crushed, causing serious head and neck injuries.
In addition to petitioning the National Highway Traffic Safety Administration (NHTSA) to adopt higher standards, the IIHS is urging semitrailer manufacturers to voluntarily improve underride guards.
Semitrailer underride guard crash tests
The push for stronger guards began in 2011, when IIHS reported that its research had demonstrated that the minimum strength required by regulators was inadequate. A review of 115 crashes in which passenger vehicles rear-ended heavy trucks or semitrailers found that almost half of the passenger vehicles suffered severe underride damage.
In 2011, there were 260 passenger vehicle occupants killed in rear-end collisions with large trucks, IIHS says. That was down from 460 deaths in 2004, but IIHS attributed the decline to an overall drop in traffic on the nation's highways. During economic recessions, traffic typically diminishes and there are fewer accidents.
Although the IIHS is awaiting a response from federal regulators to its request for higher standards, it reports that some semitrailer manufacturers have begun installing guards that are stronger than required.
The new guards generally work well, except in crashes in which a passenger car strikes the rear corner of a trailer, Rader says. The IIHS underride guard tests have raised manufacturers' awareness of safety problems, he adds.
"Since we started publicizing the results of our tests, underride guards have been improving," Rader says.
The effectiveness of underride guards depends on the type of collision, IIHS has found. The agency has tested semitrailers from the eight largest manufacturers. All of the semitrailers had guards that met both U.S. and Canadian standards for durability.
In each test, a passenger vehicle struck a parked trailer while traveling 35 mph. In the first test, cars struck the center of the rear of each trailer and all eight underride guards successfully prevented the vehicles from becoming wedged underneath. In the second test, in which only half the width of the car overlapped with the trailer, all but one trailer passed.
However, when the overlap between the car and the semitrailer was reduced to 30 percent of the car's width, only one semitrailer -- from the Canadian manufacturer Manac -- passed the test.
How to make semitrailer underride guards safer
Richard Weinblatt, a former patrol officer who serves as dean of the School of Public and Social Services at Indiana's Ivy Tech Community College, has seen the results of many collisions between passenger vehicles and semitrailers.
When cars are forced beneath semitrailers, injuries typically are devastating, he says. Weinblatt is in favor of anything that can be done to give passenger car occupants a better chance of survival.
"You want to stop the vehicles from going underneath [the semitrailers] and chopping the roofs off the cars," he says.
Rader says IIHS officials are hoping that manufacturers will continue to strengthen underride guards voluntarily. Lew Grill, an accident investigation consultant who has conducted research for the Federal Motor Carriers Safety Administration, says if the guards are made too strong, it could result in greater damage to passenger vehicles.
Guards that can bend when struck absorb energy that otherwise would crush cars that rear-end semitrailers, he explains. If the guards are made too rigid, the effect could be like driving into a wall, he adds.
Stephen Keppler, executive director of the nonprofit Commercial Vehicle Safety Alliance, says the underride guard issue deserves more study. Like Grill, he says it's important to make sure that underride guards continue to absorb adequate energy to reduce damage to passenger vehicles.
"You could have unintended consequences if you make the design too stiff," he says. "What they have incorporated into designs are energy-absorbing solutions, so when you have an impact it is not like hitting a brick wall."
Rader disagrees. IIHS tests show that driving beneath a semitrailer poses a much greater danger of injury than hitting a stiff underride guard, he says.
"When underride guards stay in place, our tests show that drivers will be able to walk away from those crashes without serious injuries," he adds.
Current federal standards for underride guards were created at a time when passenger vehicles were not as crashworthy as they are today, Rader explains. "They thought was that the underride guard had to have some give to it to reduce force for people in passenger vehicles, but our tests clearly show that is not the case."
Grill says accidents often occur because drivers of passenger vehicles don't understand the danger of following a semitrailer too closely.
"It's higher, it's longer, it's heavier," he says. "It is more cumbersome to operate. It takes two times as long for a truck to stop as a car. Maneuvering that truck is like maneuvering the Queen Mary."