The most safety-critical events for truck drivers occur on the first day following an hour-of-service restart. That confirms previous data that showed most accidents occur in the first hour the driver is on the road.

Those are the conclusions of a new study from the Virginia Tech Transportation Institute (VTTI). However, the analysis showed no relationship between the duration of the restart period or differences between the safety of all hours after the first hour of the day.

In a study funded by the Federal Motor Carrier Safety Administration, VTTI compiled data from November 2005 to May 2007, collecting video data of 100 Class A CDL drivers at four fleet companies at seven locations. The video was analyzed to spot extreme situations such as longitudinal acceleration, time-to-collision, swerving, and lane deviations, the Institute said. “Naturalistic data collection is collection data behavior and performance data in a natural environment,” said Dr. Richard Hanowski, director of the center for truck & bus safety for VTTI. “We really bring the lab into the field by putting ‘instrumented’ trucks into the real world.”

There were a total of 2,899 safety-critical events documented in the study, which analyzed crashes, near crashes, and “crash-relevant conflicts,” where a crash was possible but avoided more easily than in a near crash. Over the course of the study, there were 13 crashes and 61 near crashes, VTTI said. “The data has a high validity because you're collecting data in the real world, but low control, because it is based on what is really going on in a driver's normal routine,” Hanowski added.

According to VTTI's Myra Blanco, long-haul drivers average a 48-hour restart; medium haul, 53 hours; and short haul, 63 hours, all far more than the 34-hour restart required by FMCSA. However, the length of restart did not show any relationship to the number of incidents, she said, although results indicate that drivers get far more sleep per day during the restart (7.2 hours) than in a regular workday (6.1 hours).

The previous study found no statistical difference between the second and eleventh hour of driving, but the first hour of any day was the most likely to have a safety event. The authors hypothesized this was due to heavy traffic conditions, sleep inertia, or an increase in complex driving situations typical in the first driving hour.