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.
Trolleybus
Trolleybuses can optionally be equipped either with limited off-wire capability—a small diesel engine or battery pack—for auxiliary or emergency use only, or full dual-mode capability. A simple auxiliary power unit can allow a trolleybus to get around a route blockage or can reduce the amount (or complexity) of overhead wiring needed at operating garages (depots). This capability has become increasingly common in newer trolleybuses, particularly in North America and Europe, where the vast majority of new trolleybuses delivered since the 1990s are fitted with at least limited off-wire capability. These have gradually replaced older trolleybuses which lacked such capability. In Philadelphia, new trackless trolleys equipped with small hybrid diesel-electric power units for operating short distances off-wire were placed in service by SEPTA in 2008 are, instead of using a conventional diesel drive train or battery-only system for their off-wire movement.
King County Metro in Seattle, Washington and the MBTA in Boston use or have used dual-mode buses that run on electric power from overhead wires on a fixed right-of-way and on diesel power on city streets. Metro used special-order articulated Breda buses with the center axle driven electrically and the rear (third) axle driven by a conventional power pack, with electricity used for clean operation in the downtown transit tunnel. They were introduced in 1990 and retired in 2005, replaced by cleaner hybrid buses, although 59 of 236 had their diesel propulsion equipment removed and continue (as of 2010) in trolley bus service on non-tunnel routes. The MBTA uses dual-mode buses on its new (2004-opened) Silver Line (Waterfront).