The standardized container made intermodal possible. A box built to ISO dimensions locks onto a vessel cell, a railcar, and a road chassis equally well, so freight can cross an ocean and a continent with the doors opened once, at destination. Capacity across the whole system is counted in TEU, and a typical ocean freight import is intermodal almost by definition: vessel to the port, then rail or truck inland.

The cost case is strongest on long inland legs. Rail moves a container for less per mile than a truck once the haul stretches past several hundred miles, which is why a box from Shanghai to Chicago typically rides rail from the West Coast rather than rolling the whole way on a chassis. The trade is variability: trains run on fixed schedules, containers can sit at ramps waiting for a slot, and a missed connection adds days, not hours.

Every intermodal move starts and ends with drayage, the short truck legs connecting ports and rail ramps to docks, and those legs cause a disproportionate share of the failures. Sound logistics planning treats intermodal transit as a range rather than a date and sizes inventory buffers accordingly.