The Arizona Department of Public Safety says the truck collided with another vehicle and then struck a freeway wall. That's when the back door opened and the guard was ejected.
The accident occurred on westbound I-10 at Speedway Boulevard during the Monday morning commute, closing two lanes so DPS could investigate the accident.
The lane closures caused a backup of westbound I-10 for more than two miles. The Department of Transportation urged travelers to take alternate routes.