It is usually a single-deck design, and comprises two rigid sections linked by a pivoting joint (articulation) enclosed by protective folding bellows on the in- and outside of the vehicle (usually of gray or black colour) and a cover plate on the inside of the vehicle. This arrangement allows a longer legal overall length than single-decker rigid-bodied buses, and hence a higher passenger capacity, while still allowing the bus to maneuver adequately on the roads of its service route. [Source]