Final answer:
The intermodal option that combines truck and rail transportation with trailers on rail flatcars is called "trailer on flatcar" or TOFC, which is part of the intermodal transportation system.
Step-by-step explanation:
The intermodal option that combines truck and rail transportation, with conventional road trailers carried atop rail flatcars for the long segment of the transit, is known as trailer on flatcar or TOFC. This method is part of a broader category referred to as intermodal transportation, which played a significant role in reshaping global manufacturing and shipping logistics by reducing costs and increasing efficiency. Intermodal transportation involves using the same container or vehicle in different modes of transport, such as road, rail, and ship, without handling the freight itself when changing modes.