"A well car, also known as a double-stack car or stack 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 which 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 loading gauge assures sufficient clearance. The top container is held in place either by a bulkhead built into the car, or through the use of inter-box connectors." (copied from wikipedia)
An NX8 model would be ideal, parasolid or step would work as well.
There is a model in google sketchup, but I can't translate it. If anyone can translate it to step or parasolid.
if this link doesn't work go to http://sketchup.google.com/3dwarehouse and search "intermodal well car.
Thanks in advance.