A United Parcel Service truck pulling a single trailer drifted off the shoulder of Interstate 405 just north of State Route 527 in Bothell Tuesday morning, drove into a ditch and rolled over.

The driver suffered minor injuries and was transported to Evergreen Hospital for evaluation, according to Washington State Patrol (WSP) Trooper Keith Leary.

The incident occurred at 5:40 a.m., caused a traffic backup of four miles and the road was fully reopened at 9 a.m., according to the Washington State Department of Transportation.

Leary noted that WSP and commercial-vehicle workers were trying to determine whether the driver fell asleep at the wheel or if there was mechanical problems with his vehicle. Commercial-vehicle workers ruled out mechanical troubles, Leary added.

No citation has been given to the driver at press time.