Final answer:
The abbreviation for a truck trailer placed on a flat railcar for train transport is TOFC, which stands for Trailer on Flat Car.
Step-by-step explanation:
The abbreviation for a truck trailer that is placed on a flat railcar and then pulled by a train engine is TOFC, which stands for Trailer on Flat Car. When trailers are transported this way, it's a part of intermodal freight transport, allowing for the integration of different transportation methods, like trucking and rail, for the efficient movement of goods.