These are semi-trailers that may no longer be used over the road, but which have been maintained in "wind & water tight" condition for commercial storage uses. For many commercial and industrial firms, they provide a more flexible and cost efficient alternative to acquiring additional warehouse or shop space for shorter term storage needs. They are particularly useful if all loading/unloading will be done at dock level rather than ground level. Some of the 48 foot trailers are 8 1/2 feet wide to hold more pallets side-by-side.