Abstract: Employee #1 was changing a pinion seal in a transmission. The vehicle, a 35 foot long Pace Arrow, had been backed into the work bay. Due to its length, the front end of the vehicle remained out on the downward sloping ramp. The employee placed the unit in neutral (it does not have a park position) and applied the parking brake, locking the transmission. He did not put a wheel chock in place. He crawled under the rig and disconnected the universal on the drive shaft. This allowed the rear axle to turn and the unit started rolling away. The employee rolled out from under the unit, chased it down, and started opening the driver's side door when the unit struck a parked Ford 9000 LTL tractor (for a tractor trailer) a glancing blow. Employee #1 was pinned between the vehicles until rescued by fire fighters using airbags. He sustained multiple injuries, but was not hospitalized.