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.
GM Buffalo bus
In 1966, GM introduced the PD-4107. Also known informally as "decks", these buses were similar in some ways to the Scenicruiser design, but had a larger "second level" with the first level reduced, and the lavatory was located at the rear. The 4107 was in length, and nominally (without lavatory) would seat 41 passengers (38 or 39 with lavatory). In 1968, the PD-4903 was introduced, a long version of the 4107 which nominally would seat 49 passengers (46 or 47 with lavatory). The PD-4903 was the first GM bus to use a 24 volt electrical system and was 40 feet long with a third luggage bay. For states with lower axle load limits, a factory option used the third bay to hold a retractable two-tire axle.