A double-decker bus or double-deck bus is a bus that has two storeys or decks. They are used for mass transport in the United Kingdom, the United States, New Zealand, Europe, Asia and also in cities such as Sydney; the best-known example is the red London bus, namely the AEC Routemaster. Double-deckers are primarily for commuter transport, but open-top models are used as sight-seeing buses for tourists. William Gladstone, speaking of London's double-deck horse-drawn omnibuses, once observed that "...the best way to see London is from the top of a bus".