According to research from the Virginia Tech Transportation Institute (VTTI), the most safety-critical events for truck drivers occur in the first day following an hour-of-service restart, that tracks with previous data that showed the most accidents occur in the first hour the driver is on the road.

However, the analysis showed no relationship between either the duration of the restart period or differences between the safety of all hours after the first of the day, including in the eleventh hour.

In a study funded by the Federal Motor Carrier Safety Administration, VTTI compiled data from November 2005 to May 2007, collecting video and data of 100 Class A CDL drivers at four fleet companies at seven locations. VTTI said it preferred to do its research in the field, rather than in a controlled environment. 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 2899 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 the restart did not show any relationship to the number of safety incidents, she said, although results indicate that drivers get far more hours of 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 that the first hour of any day was the most likely to have a safety event. The study authors hypothesized that this was due to heavy traffic conditions, sleep inertia, or an increase in complex driving situations typical in the first driving hour.

In the future, VTTI hopes to take a look at the impact of non-driving activities on safety events. “We have good data on drivers actually driving, but not as much on when drivers are off duty—what they’re eating, medications they’re taking, what they’re doing on a day off,” said Hanowski.

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