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.
Bus conductor
Bus conductors (also referred to as conductors, or clippies) were a common feature of many local bus services in larger towns and cities in the UK and Ireland, until the late 1970s and early 1980s. The main reason two-person crews were needed was that most towns and cities used double-decker buses for urban services. Until the 1960s, all double deck vehicles were built with front-mounted engines and a "half-cab" design, like the familiar AEC Routemaster London bus. This layout totally separated the driver from the passenger saloons. The conductor communicated with the driver using a series of bell codes, such as two bells to start (the well-known "ding-ding").