WALES — The driver of a dump truck hauling gravel was killed Friday morning when the truck rolled over on Route 126.

Chief Deputy William Gagne of the Androscoggin County Sheriff’s Office said investigators are looking into the possibility that a medical issue caused the crash. The truck was headed toward Monmouth shortly before 7 a.m. when it left the roadway and rolled over, he said.

The driver was the sole occupant of the vehicle; no other vehicles were involved, Gagne said.

Authorities are withholding the name of the driver pending notification of next of kin.

Route 126 was closed to traffic for several hours, he said.

The Sheriff’s Office is conducting an accident reconstruction, which is considered best practice in fatal accidents, Gagne said.

The Maine State Police Commercial Vehicle Enforcement Unit assisted at the scene, along with fire departments from Monmouth, Wales and Sabattus as well as Sabattus Police Department.