Abstract: A trolley system for positioning the door of a railway boxcar to cover or uncover an opening in a wall of the boxcar has an upper track mounted to the boxcar and an upper trolley with at least one roller rotatably secured therein and co-acting with the upper track. A safety plate restricts the vertical motion of the roller to prevent derailment of the trolley from the track. The safety plate may include various designs to maximize the retention of the wheel against the track. A boxcar utilizing either a simple sliding door or a sliding door having a plug-type door associated with it may utilize this trolley system.