Double-decker bus
With the exception of coaches, double-decker buses are uncommon in the United States. Many private operators, such as Megabus, run by Coach USA, employs double-decker buses on its busier intercity routes.
Trailer bus
During World War II and in the immediate post-war years, trailer buses were turned to as a simple and economical way of providing bus transport to replace worn out conventional bus fleets. The semi-trailers were basic and uncomfortable, but each could carry more passengers than an ordinary single-decker bus, and nearly as many as a double-decker bus. Indeed BEST of Mumbai, India had ten double-decker trailer buses in her fleet during the 1970s.