Note: Sequences such as 22G1 refer to ISO container size and type codes.
The initial container sizes were the 20-footer (22G1) and the 40-footer (42G1), dimensions that were agreed upon in the 1960s and became an ISO standard. Initially, the 20-footer was the most widely used container. However, as containerization became widely adopted in the 1990s, shippers switched to larger container sizes, notably the 40-foot container. Larger sizes confer economies of scale in loading, handling, and unloading, which are preferred for long-distance shipping as well as by customers shipping large batches of containerized commodities. The same ship capacity would take, in theory, twice as much time to load or unload if 20-footers were used instead of 40-footers. There is thus an evident rationale to use the largest container size possible.
“Hi-cube” containers (45G1) have also been put in use since they do not require different handling equipment or road clearance. They are one foot higher (9’6″) than the standard 8’6″ height, and a 40-footer hi-cube container provides about 12% more carrying capacity than its standard counterpart. Most North American double-stack rail corridors can handle two stacked hi-cube containers, creating an additional multiplying effect in terms of total capacity per rail car. The 53-foot hi-cube container (P5G1), which is the maximum length permitted on the American Interstate highway system, is a load unit that would enable carrying even more low weight cargo (42% more volume than a 40-foot high cube container). However, it is not commonly used since it can only be stacked in the upper section of containerships and does not fit into their bellyhold designed to accommodate 40-foot containers.
The European Union is trying to implement a new container labeled the European Intermodal Load Unit (EILU), which would have a length of 45 feet and a width of 8.5 feet (LEG1). The rationale behind this initiative is that it would allow two of the standard European pallets to be loaded in containers side by side as existing containers are based on North American pallet dimensions. While the new dimensions would still meet clearances for road and rail transport in Europe as well as abroad, the EILU is not being adopted internationally. Shipping lines have huge accumulated investments in current equipment, and new ships under construction are optimized for existing ISO container sizes. Because containers have a useful life of about 12 to 15 years, intermodal carriers are reluctant to adopt any new standard because of prior commitments in capital investment in modal and intermodal infrastructures.