In addition to the cable and winch, which is okay of there's only one siding and the cars are going only in one direction, there's also a trackmobile.
This is like a small speeder with 4 metal wheels on 2 axles that straddles the rails. At one end, there's your standard coupler to couple to the car to be moved.
90° to the metal wheels are 4 rubber tires on 2 axles. The operator's cab hangs over the side of the rails. To get the trackmobile off the rails, the operator simply lowers the rubber tires which jacks up the track mobile. He drives out of the tracks and away down the road to the next car.
For MasonJar, there used to be one at the Hershey plant in Smiths Falls.
PS - Haven't heard from you since January 4th. Are you still interested? Reply offline