The agency takes an annual snapshot of drivers' behavior behind the wheel by staking out intersections to count people using cellphones and other devices, as well as other distracting behavior.
Driver distraction wasn't the only significant safety problem uncovered by NTSB's investigation of the Missouri accident. Investigators said they believe the pickup driver was suffering from fatigue that may have eroded his judgment at the time of the accident. He had an average of about five and a half hours of sleep a night in the days leading up to the accident and had had fewer than five hours of sleep the night before the accident, they said.
The pickup driver had no history of accidents or traffic violations, investigators said.
Investigators also found significant problems with the brakes of both school buses involved in the accident. A third school bus sent to a hospital after the accident to pick up students crashed in the hospital parking lot when that bus' brakes failed.
However, the brake problems didn't cause or contribute to the severity of the accident, investigators said.
Another issue involved the difficulty passengers had exiting the first school bus after the accident. The bus' front and rear bus doors were unusable after the accident — the front door because the front bus was on top of the tractor truck cab and too high off the ground, and the rear door because the front of the bus had intruded five feet into the rear of the first bus.
Passengers had to exit through an emergency window, but the raised latch on the window kept catching on clothing as students tried to escape, investigators said. Exiting was further slowed because the window design required one person to hold the window up in order for a second person to crawl through, they said.
It was critical for passengers to exit as quickly as possible because a large amount of fuel puddled underneath the bus was a serious fire hazard, investigators said.
"It could have been a much worse situation if there was a fire," Donald Karol, the NTSB's highway safety director, said.