Understanding why large trucks crash is key to developing countermeasures to reduce those crashes. New IIHS-sponsored research shows that serious vehicle defects triple the risk of being involved in a crash. Long hours behind the wheel and use of the short-haul exemption for federal hours-of-service rules also are important contributors to crashes.
In 2015, 3,852 people died in crashes involving large trucks. Sixteen percent of these deaths were truck occupants, 69 percent were passenger vehicle occupants and 15 percent were pedestrians, bicyclists or motorcyclists.
IIHS has been studying serious crashes involving large trucks for decades, and, although the outlook has improved, IIHS research shows unsafe trucks and tired truckers persist. During the 1980s, the Institute studied large truck crashes in Washington and found that tractor-trailers with defective equipment were twice as likely to crash as trucks without defects (see "Truck defects double the danger," Sept. 19, 1987).
The latest study updates that research and for the first time looks at the short-haul exemption's effect on crash risk. Drivers who work for an interstate carrier and operate within a 100-mile radius of their work base can apply for the exemption if they work fewer than 12 hours a day and don't make overnight trips.
IIHS researchers partnered with the University of North Carolina Highway Safety Research Center and the North Carolina State Highway Patrol to investigate factors that affect crash risk for large trucks operated by interstate carriers. Researchers compared large trucks involved in serious crashes in North Carolina with injuries or deaths during 2010-12 with a sample of similar trucks that weren't involved in crashes. The matched case-control design allowed researchers to compare the relative prevalence of various factors to determine which ones are associated with increased crash risk.
Researchers collected data on a total of 197 crash and control pairs. More than a third of crashes were fatal and 17 percent involved an incapacitating injury. Crashes were more likely to occur during the daytime and to involve another vehicle besides the tractor-trailer.
Vehicle violations raise crash risk
Nearly three-quarters of the crash-involved trucks had vehicle defects identified during a post-crash inspection. Trucks with out-of-service violations for any type of defect were more than 4 times as likely to be in a crash as trucks without such violations. The crash risk for a truck with any out-of-service vehicle defect deemed as the striking vehicle in a multiple-vehicle crash was 10 times as high as the risk for comparable trucks without vehicle defects.
A commercial motor vehicle inspector can issue an out-of-service order for a mechanical or loading problem that makes the truck a serious hazard on the road and would likely cause a crash or breakdown. Examples include faulty brakes, fraying sidewalls on tires and burned out headlights, taillights or brake lights.
Having vehicle defects of any type raised crash risk. Trucks cited for brake violations were 50 percent more likely to crash than the comparison trucks, and out-of-service brake violations tripled crash risk. Tire and lighting system violations were generally associated with bigger increases in crash risk, but researchers caution this may be the case in part because some of the violations inspectors flagged resulted from crash damage.
"Highway patrol officers and roadside inspectors serve as the front line of defense when it comes to spotting unsafe trucks, and these efforts should continue," says Eric Teoh, a senior statistician with the Institute and the study's main author. "Defects on 40-ton vehicles are a serious threat to highway safety."
Carriers with higher past crash rates were associated with an elevated current crash risk. Firms with at least 100 reported crashes per 1,000 power units (tractors or single-unit trucks) within the preceding 24 months had a 72 percent higher risk of crashing than carriers with fewer than 100 reported crashes per 1,000 power units.
"Some trucking groups have suggested that carriers shouldn't be penalized for crashes that weren't the fault of the driver or were unpreventable, but these results show counting all crashes is meaningful. We don't always know who was at fault in crashes, and if something about a carrier's operation puts them at high risk for not-at-fault crashes, that's important to know too," Teoh says.
Tired truckers and short-haul exemption are factors
Looking at driver-specific factors, researchers found that truckers age 60 and older had a higher crash risk than drivers ages 30-59, who made up 72 percent of the crash-involved drivers in the study.
Truckers who reported driving after at least 12 hours since an extended sleep period were 86 percent more likely to crash than drivers who had been awake for less than eight hours. Truckers who reported driving more than five hours without stopping were more than twice as likely to crash as those who drove 1-5 hours.
Hours-of-service regulations govern how much time truck drivers can be on the road and when and for how long they need to rest. The current regulations allow up to 11 hours a shift and up to 77 hours over seven days (see "Final hours-of-service rule leaves 11-hour shift intact," Jan. 24, 2012, and "Truckers still need more rest than plan allows," April 26, 2011). Driver fatigue is a significant contributor to crashes involving large trucks.
The new mandate for electronic logging devices (ELDs) set to take effect in late 2017 should help reduce the problem by making it harder for drivers to fudge the time they really spend on the highway without sufficient rest (see "Long haul: Mandate for electronic logging devices is finally on the books," Feb. 26, 2016).
Although short-haul drivers must comply with federal rules on work and rest times, they don't have to record their service hours.
Researchers found that the crash-involved trucks whose drivers operated under a short-haul exemption were less likely to operate on interstates and more likely to involve owner-operators and single-unit trucks. These trucks logged fewer miles per year than other trucks. Researchers found that drivers using a short haul exemption had a crash risk nearly 5 times as high as those who weren't. What is more, short-haul trucks were more likely to have inspection violations than other crash-involved trucks.
Teoh says he was surprised that the data showed a higher crash risk for trucks operating under the short-haul exemption.
"Short-haul trucks are used differently and may be more at risk if they have vehicle defects," Teoh says. "The short-haul exemption merits a more in-depth look to understand what's really going on."
Safety technologies can lower crash risk
Several safety features showed promise in reducing crash risk among the large trucks in the study. Antilock braking systems for large trucks reduced the risk of crashing by 65 percent. Antilock brakes, which keep wheels from locking during hard braking, improve driver control of large trucks during emergency stops and reduce the likelihood of a tractor-trailer jackknifing. Antilocks have been required on new tractors since 1997 and on new trailers, single-unit trucks and buses since 1998.
"We also found benefits for electronic and roll-stability control, speed governors and electronic logging devices," Teoh adds.
ESC will be required on tractor-trailers and buses as of August 2017 (see "Truck tractors, large buses will get ESC under new rule," July 30, 2015). A mandate for speed limiters also is under consideration, along with a requirement that trucks with a gross vehicle weight rating of 10,000 pounds or more have a forward collision warning system with automatic braking (see "Front crash prevention may be required for large trucks," Feb. 26, 2016).
Deaths in crashes involving large trucks, 1975-2015
Percent difference in crash risk
Vehicle safety violations predict crash risk …
… as driver factors also come into play