Here in the U.S., containers that are transported only on trains and by truck are usually 53 feet long. This coincides with the maximum length of a trailer for a tractor-trailer combination on almost the entire U.S. interstate highway system.
You may also find some 48-foot containers out there. China tried using them in international shipping for a while, but it was just too unwieldy to stack them with 20-foot and 40-foot containers. So they are generally used as smaller versions of the 53-foot containers you see here in domestic U.S. shipping.
Interesting stuff - thanks for sharing.