Double-Stack
Double-Stack is a rail transport technique in which containers are carried stacked two high on specialised well cars (whose lowered floor keeps the double load within height limits). By carrying twice the containers per railcar and per train, double-stacking dramatically improves the capacity and cost-efficiency of intermodal rail.
Pioneered and dominant in North America, where generous rail clearances and long trains suit it, double-stack has transformed container-on-rail economics for moving boxes between ports and inland terminals, and along land bridges across the continent. Its main constraint is vertical clearance — tunnels, bridges and overhead electrification must be high enough — which is why it is less widespread in regions with tighter loading gauges (though clearance projects have extended it). Double-stack is a key enabler of efficient, high-volume intermodal rail freight and a major reason rail is competitive for long-haul container movement in the markets that can accommodate it. It relates closely to intermodal transport, rail freight and land bridges.
Double-stacking doubles the containers a train can carry, transforming the economics of moving boxes inland by rail — which is why it dominates North American intermodal and land-bridge traffic. Its dependence on vertical clearance explains why rail competes so well for containers in some regions and not others, making it key to understanding intermodal rail economics.
What is a well car?
A railcar with a lowered floor that lets two stacked containers stay within height limits, enabling double-stacking.
Why is double-stack limited in some regions?
It needs high vertical clearance under tunnels, bridges and overhead wires, which many rail networks outside North America lack.