Southern Pacific, in 1953, ran truck trailers on flatcars as piggyback

Trucks could pick up and deliver at any dock, but a truck moving cargo across the country spent a long time on the road. Rail could move freight cheaply between cities but could not serve every door. Each mode had half the answer.

Southern Pacific made the two modes one system in 1953 by putting highway trailers directly onto flatcars — the piggyback service, or trailer-on-flatcar. The trailer rolled to the railhead, the rail carried it between cities, and another tractor finished the trip. The cargo itself was never unloaded.

That kept the convenience of door-to-door trucking while giving the long intercity leg the cost of rail. The carrier did not have to win the whole trip with one mode; it just had to hand the same box off.

Southern Pacific ran its first commercial TOFC service in 1953 on the Los Angeles–San Francisco corridor, and the idea caught on quickly enough that dozens of railroads adopted it within a few years.

Make the trailer the unit that rides both modes

The trailer stays intact, so goods are handled once at each end instead of transferred between truck and train.

Rail covers the long, fuel-heavy leg while trucks handle the short, time-sensitive ends.

A carrier does not need to own both a long-haul truck fleet and a rail line to offer a complete service.

TOFC gave railroads a way to win back traffic that trucks were taking on medium-distance lanes.

Intermodality works when the load unit stays intact across modes — the box that moves is more valuable than the mode that moves it.

Trailer-on-flatcar spread to 42 North American railroads within about five years and became the ancestor of modern intermodal. When containers replaced highway trailers as the unit, the door-to-door rail-truck model grew into the global intermodal network that carries most long-distance freight.