Underride guards are required on most semi trailers. These are bars that hang from the back of a trailer to keep vehicles from sliding under the trailer in the event of a crash. Research showed that these steel bars’ minimum dimensions and strength previously required for safety purposes were not adequate for preventing serious injuries or fatalities, so the National Highway Traffic Safety Administration was asked to take action in 2011.
In response to this news, many manufacturers began putting stronger guards on their products. With the exception of crashes at outer trailer edges, these guards tend to work better to prevent underride-related injuries. Although the requirements did not come from government entities, experts believe manufacturers are doing this to keep up with their competitors in Canada where such regulations exist. However, experts decided to conduct tests on the latest guards.
Researchers took trailers from eight major manufacturers to test for guard effectiveness. Through a progressive series of crash tests, they noted that all of the trailers had guards that not only met American standards but also the tougher Canadian standards. A guard that is strong enough to withstand a specific amount of force is required under both sets of standards. The Canadian standard requires a trailer to withstand about twice as much force as the American standard does.
The improvements made to protect occupants have lowered crash deaths recently when a car’s front end winds up under a trailer. The top of the car is crushed due to the structures that are made to absorb impact being bypassed. Safety belts and airbags are unable to function as they should, and any occupants may sustain life-threatening injuries. Tests showed researchers how this happened. One of the top-rated vehicles was chosen to undergo a moderate overlap barrier test, which was used to evaluate crash responses. When the guards stayed up properly, the test showed no serious injuries to the dummy in the vehicle. However, they showed serious injuries when the guards failed. The injury rates were so high that actual drivers would have perished.
Researchers found that 260 of the more than 2,200 vehicle occupants involved in fatal crashes with large trucks died after their vehicles crashed into the rear ends of trucks. This number was down from the 460 of nearly 3,700 in 2004. Experts say this decline is likely attributed to changes in vehicle traffic in a weak economy. Data gaps make it hard to show exactly how many crashes were attributed to underrides. A study conducted in 2011 showed that only about 20 percent of crashes involved negligible underride work or no underride. Of this number, about half of the vehicles had catastrophic or severe damages to the underrides.
Trailers undergo multiple overlap tests, and researchers found that several failed the 50 percent test, which they said is a big problem. While many trailers passed this test, a large majority had difficulties with the 30 percent overlap test. The main problem came from the underride guard vertical support location. With most trailers, supports are affixed to the slider rails, which are bars that run lengthwise under trailers and allow the wheels to change based on the load. With this structure, vertical supports are located about 28 inches away from the edge of the trailer. The only trailer that passed the 30 percent test used a special reinforced floor, which was spaced 18 inches from the edge. The guard was attached to this reinforced floor. In addition to being safer to oncoming traffic, it also suffered less total damages to the trailer than other units did.
Experts say that if trailer manufacturers can make better quality guards that protect occupants better and also cost less to repair, that will be a huge win. They also say they are waiting for NHTSA to enforce stricter standards, but they hope trailer buyers will be responsible enough to ensure their selections are as safe as possible whether new regulations are developed or not.