A well car, also known as a double-stack car (or also intermodal car/container car), is a type of railroad car specially designed to carry intermodal containers (shipping containers) used in intermodal freight transport. The "well" is a depressed section that sits close to the rails between the wheel trucks of the car, allowing a container to be carried lower than on a traditional flatcar. This makes it possible to carry a stack of two containers per unit on railway lines (double-stack rail transport) wherever the structure gauge assures sufficient clearance.
The top container is secured to the bottom container either by a bulkhead built into the car — possible when bottom and top containers are the same dimensions, or through the use of inter-box connectors (IBC). Four IBCs are needed per well car. In the terminal there are four steps: unlock and lift off the top containers of an inbound train, remove the bottom containers, insert outbound bottom containers, lock assembly after top containers emplaced. Generally this is done car-by-car unless multiple crane apparatus are employed.