A domestic intermodal move is: a dray carrier picks up a container, takes it to a rail ramp, the railroad line-hauls it across the country, and a dray carrier at the destination ramp delivers it. The container is never opened in between.
Intermodal trades transit time for cost. On long lanes it is cheaper and more fuel-efficient than over-the-road truckload, but it is slower and less flexible — ramp schedules, rail congestion, and the two drayage moves add days and coordination.
It works best for freight that is not time-critical, moves in consistent volume on long lanes with good ramp pairs, and can tolerate the extra handling risk at the ramps.
Example
A manufacturer ships steady weekly volume from Chicago to Los Angeles. Rather than pay a team-driver truckload rate for a two-day transit, it books intermodal: dray to the Chicago ramp, rail to LA over about four days, dray to the consignee. The rate is well below the truckload equivalent, and the extra two or three days are acceptable for this product.
Why it matters
On long, non-urgent, high-volume lanes, intermodal can undercut truckload by a wide margin. A carrier that only quotes over-the-road loses those lanes to rail; one that can offer both keeps the freight.