A truck driver involved in an accident last week that killed seven children had been awake for 34 hours, the Associated Press reports.Alvin Wilkerson, 31, was driving a load of bottled water to Jacksonville, Fla., when he plowed into a car at a school bus stop. David Rayburn, a National Transportation Safety Board investigator, said fatigue was one of many factors being reviewed.Wilkerson, who has not been charged with any wrongdoing, has refused to speak with investigators. Blood test showed he had not been using alcohol or drugs and was not using his cell phone at the time of the accident. The truck did not experience mechanical failure.The NTSB, using an identical school bus and truck, determined the school bus should have been visible for more than half a mile. The truck left some light skid marks before hitting the car and pushing it into the school bus.According to the Federal Motor Carrier Safety Administration (FMCSA), more than 750 people die and 20,000 more are injured each year due directly to fatigued commercial vehicle drivers.Large trucks are involved in multiple-vehicle fatal crashes at twice the rate of passenger vehicles, according to government statistics. Almost 800 large truck occupants, almost all of them drivers, die each year in these crashes, the Advocates for Highway and Auto Safety says. In recent years, almost one of every four fatalities among passenger vehicle occupants have been the result of multi-vehicle collisions involving a large truck.