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.
Single-deck bus
A single-decker bus or single-decker is a bus that has a single deck for passengers. Normally the use of the term "single-decker" refers to a standard two-axled rigid bus, in direct contrast to the use of the term double-decker bus, which is essentially a bus with two passengers decks and a staircase. These types of single-deckers may feature one or more doors, and varying internal combustion engine positions.