it's about the most freight per load. When I was at Frito Lay we had a fleet of almost exclusively 53ft trailers, though a few 48 ft trailers would find their way west, FL used the 48ft trailers mostly on the east coast I95 corridor because of the tighter service area. We would sometimes end up with 57ft trailers in the traffic ctr, but because they required permits for excessive length they would pretty much find their way to the south and midwest due to carless dispatchers or lazy drivers.

You still see the 40ft from time to time, food service and LTL. However the AMT versions are very much dated being from the early 70's. not likely you'd see very many of those in regular freight service these days...probably more likely as tool trailers or storage trailers.