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. Early double-deckers put the driver in a separate cab. Passenger access was via an open platform at the rear and a bus conductor collected fares. Modern double-deckers have a main entrance door at the front and the driver takes fares, thus halving the number of workers aboard, but slowing the boarding process. The rear open platform, popular with passengers, was abandoned for safety reasons, as there was a risk of passengers falling when running and jumping onto the bus. 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". By country Cities listed here have double-decker buses as part of their regular mass transit fleet. Cities with only tourist and sightseeing double-decker buses are excluded. Europe In the European Union, the maximum height for any vehicle is 4 metres, for motor vehicles in categories M2 and M3 and their trailers in category 0 and motor vehicles in categories N2 and N3 and their trailers in categories 03 and 04, in national and international traffic according to Council directive 96/53/EC of 25 July 1996 and in continuity of council directive 85/3/CEE. The United Kingdom has a triple standard for the double-decker bus: highbridge bus (urban Britain), lowbridge bus (countryside Britain) and 4 metres height coach such as the Neoplan Skyliner that can traverse Europe. United Kingdom The first commercial horse-drawn double-decker omnibuses were introduced in England in 1847 by Adams & Co. of Fairfield, Bow; it was then improved upon by John Greenwood, who introduced a new double-decker in 1852. Double-decker buses are in common use throughout the United Kingdom and have been favoured over articulated buses by many operators because of the shorter length of double-deckers and larger seating capacity; they also may be safer to operate through narrow streets and round tight corners. The majority of double-decker buses in the UK are between and long, the latter being more common since the mid-1990s, though there are three-axle models