Here's a bit more courtesy of Google.
http://hoaxes.org/weblog/comments/a_brief_history_of_triple_decker_busesThe first real triple-decker bus went into service in 1932, shuttling up to 88 passengers at a time between Rome and Tivoli. But as the picture of it below shows (from Popular Mechanics, 1932), the third level was only a small section at the rear of the bus.