In a study of national crash data on fatal two-vehicle accidents involving a heavy truck, Daniel F. Blower, assistant research scientist at the U-M Transportation Research Institute (UMTRI) found that the actions of drivers of passenger vehicles alone contribute to 70 percent of the crashes. On the other hand, truck drivers alone commit driving errors in 16 percent of the accidents, while both drivers make errors 10 percent of the time. (The remaining 4 percent of crashes do not result from driver error or have an undetermined cause.)
Taken at face value, this seems to indicate that passenger-vehicle drivers contribute disproportionately to fatal crashes involving a truck and a passenger vehicle, says Blower, who notes that the purpose of his study is not to assign blame, but to understand the full range of actions that contribute to fatal truck accidents.
One explanation for the disparity, he says, could be that since it is typically the driver of the passenger vehicle who is killed in such fatal crashesabout 40 times more often than the truck driverthe deceased driver obviously cannot give his or her side of what happened.
But Blower says that the surviving driver hypothesis is too simple. In crashes where both drivers survive, the driver of the passenger vehicle is still the primary cause more than twice as often as the truck driver.
Accident investigators, he says, have other sources of information to determine what happened in a crashbeyond deciding which drivers story to believe.
Physical evidence about what happenedwho ran into whomis a powerful indicator and usually shows that the driver of the passenger vehicle made the error that led to the collision, Blower says.
Using data from UMTRI and the National Highway Transportation Safety Administration, Blower analyzed the nearly 5,500 fatal accidents that involved one heavy truck and one passenger vehicle (car, van, sport-utility vehicle, pickup or light truck) in 1994 and 1995 (the most recent years with complete crash data).
He found that the most common crashes (nearly 23 percent) are head-on collisions in which the passenger vehicle crosses the center line into the trucks patheight times more often than a truck crosses into the lane of a passenger vehicle.
Further, Blower says, drivers of passenger vehicles are six times more likely than truckers to sideswipe a truck heading in the opposite direction, four times more likely to hit a truck from behind and twice as likely to turn across the path of a truck or sideswipe a truck going in the same direction.
The disproportion of passenger-vehicle driver errors in fatal crashes may be in a sense related to the fact that a fatality occurred, rather than that they are more culpable, he says. Rear-end collisions provide the clearest example, because a fatality is more likely to occur if a passenger vehicle strikes the rear of a truck, rather than the truck striking the rear of the passenger vehicle.
According to Blower, rear-end collisions caused by passenger-vehicle drivers may occur because of driver inattention, unsafe speed and truck conspicuity, while harder-to-explain head-on crashes may be due to alcohol use, night-time travel and weather.
It is clear that addressing the truck safety problem must take into account more than just trucks and truck drivers, he says. The actions of other vehicles on the road contribute substantially to the toll. Even if all trucks were operated perfectly, only a minority of the fatal crashes would be eliminated.
Truck crashes do not occur in isolation, but as part of a larger system, involving the roadway and environment, vehicle condition and the other vehicles in the traffic system. If we want to reduce the toll of truck accidents, we need to broaden our understanding beyond just trucks and truck drivers.