OK, so the curtain sides are a way of managing LTLs (Less than
Truckload Lots). In North America the tendency would be to load up a
trailer with goods going to the same city, then unload for city
delivery at their local terminal, onto smaller trucks (even tractor-
semitrailer rigs, but perhaps with only one driving axle and one
trailer axle), from back to front in the order of the city driver's
route.

Sometimes side access to palletized loads is required. Flatbeds are
popular for dense freight: side panels can be removed and single
pallets unloaded. The entire load can be tarped in case of inclement
weather.

One unique application for flatbeds is grass sod delivery. A miniature
fork lift truck is mounted to the back of the flatbed. The truck
driver lowers it to the ground and unloads as many sod pallets as the
homeowner has ordered.

Another is for moving household goods. One semitrailer might hold the
contents of four or five households. If, for any reason, either the
new residence or the residents are unavailable when the movers arrive,
the contents are crated up at the mover's warehouse. Then a separate
flatbed carries these huge crates when both the new home and the
customers are ready.

Yes, I think that it's probably a matter of physical geography. North
America is a vast country, but with comparatively 'compact' population
centres, and huge tracts of nothing between. That probably makes it better
to just run full trucks from one depot to another. In the UK, it is of
course much smaller, but with equally dense population centres. That makes
those centres much closer together, so makes the palletised distribution
model eminently practical. It was poularised by a woman called Hilary Devey
who now runs the biggest network in the UK if not Europe. She is a TV
personality also as one of the entrepeneurs on Dragons Den which has the
U.S. equivalent Shark Tank. It's a very practical system of distribution,
and has made her very rich.

Arfa