A lowbridge double-deck bus is a double-decker bus which has an asymmetric interior layout, enabling the overall height of the vehicle to be reduced compared to that of a conventional double-decker bus. The upper deck gangway is offset to one side of the vehicle, normally the offside (or driver's side), and is sunken into the lower deck passenger saloon. Low railway bridges and overpasses were the main reason that a reduced height was desired.