As manufacturers design new vehicles, they go through a number of tests to ensure passenger safety in the event of a crash. In fact, most cars are tested to ensure that you can walk away from any accidents that occur at 35 mph or less.
But most cars are not designed to hold up when a passenger car rear-ends a much higher-riding semi truck, even at low speeds.
According to the Insurance Institute for Highway Safety (IIHS), 3,163 people died in accidents with tractor-trailers and large truck crashes in 2009. Of those, 70 percent were occupants of passenger vehicles. IIHS president Adrian Lund noted that in many collisions involving cars and semi trucks the upper part of the car is crushed as the passenger vehicle slides under the body of the truck's trailer.
Underride guards on the back of tractor-trailers are supposed to reduce injuries and fatalities when a car crashes into the back of a large truck. But, many large commercial trucks either do not have them installed or the underride guards often fail on those trucks that do have them.
"Your vehicle could be one that earns top marks in frontal crash tests," says Lund, "but if that truck's underride guard fails - or if the truck doesn't have one at all - your chances of walking away from even a relatively low-speed crash are not good at all."
Estimates by the National Highway Traffic Safety Administration (NHTSA) suggest that over 400 people die each year and another 5,000 people are injured in underride crashes. In an effort to help reduce this number of injuries, the IIHS is petitioning NHSTA to require all large trucks to have underride guards, and also require higher standards for underride guard manufacturers.
Source: Semi Crashes Still Proving Fatal