Most deaths in large truck crashes are passenger vehicle occupants. Large trucks often weigh 20-30 times as much as passenger vehicles. They are taller and have greater ground clearance than cars, which means that lower-riding vehicles can slide beneath truck trailers, with deadly consequences. Rear underride guards are supposed to stop this from happening, but IIHS research shows that guards meeting federal safety standards can fail in relatively low-speed crashes. IIHS has petitioned regulators to require underride guards that are strong enough to remain in place during a crash and to broaden rules to mandate guards for more large trucks and trailers.
Truck driver fatigue is a known crash risk. Under federal hours-of-service regulations, drivers of large trucks are allowed to be behind the wheel for as long as 11 hours at a stretch and can log as many as 77 hours during a seven-day period. Surveys indicate that many drivers violate the regulations and work longer than permitted. Requiring electronic onboard recorders for all commercial trucks would improve compliance with federal work rules by automatically recording when a truck is driven. The recorders would replace the easily falsified handwritten logbooks drivers keep to catalog their work hours.
Truck braking capability can be a factor in crashes. Compared with passenger vehicles, stopping distances for trucks are much longer, particularly on wet and slippery roads or if the brake systems are poorly maintained. Large trucks also are prone to rolling over. A proposal to require truck tractors to be equipped with electronic stability control could help reduce crashes.
IIHS tested eight top-selling semitrailers to see how well they prevent cars from sliding underneath.