WASHINGTON — Police are looking into what caused a tractor-trailer to run over its driver, killing him Friday morning at a Montgomery County weigh station.

James Lee Hobbs, 58, of Salisbury, Maryland, was killed at about 11:30 a.m., in Hyattstown while working under the truck on its brakes, Maryland State Police said. A trooper with the Commercial Vehicle Enforcement Division stopped Hobbs for brake violations.

A preliminary investigation found Hobbs was attempting to make the necessary brake adjustments, but had failed to engage the parking brake on the vehicle. Because he was under the truck, it rolled back and killed him.

The semi-truck was empty and was located in the weigh station’s out-of-service lot at the facility at the time of Hobbs death, police spokesman Ron Snyder said.

Hobbs was declared dead at the scene. A full investigation into what happened has not yet been completed.