Single-deckers and Double-deckers

Single-deckers

The midibus is a lighter and smaller purpose-built development of the single-deck bus, which emerged in the 1990s.
Double-deckers

Where more capacity is needed, a double-decker bus or articulated bus may be used, the prevalence of which varies from country to country. A double-decker is a rigid vehicle with an extra upper deck, the two conjoined for access by a staircase— usually in modern vehicles a spiral staircase near the front, but often at the rear on older vehicles, which may have an open platform. Larger double-deckers might have both front and rear staircases.