The metropolitan area of Adelaide, South Australia is served by a wide variety of transport. Being centrally located on the Australian mainland, it forms a hub for east–west and north–south routes. The road network includes major expressways such as the Southern Expressway, the South Eastern Freeway, the Port River Expressway, the Northern Expressway and the South Road Superway. The city also has a public transport system managed by Adelaide Metro, consisting of a contracted bus system including the O-Bahn Busway (a guided busway), six metropolitan railway lines, and the Glenelg-Adelaide-Hindmarsh Tram. According to a study conducted by the Australian Bureau of Statistics, Adelaide has the highest passenger vehicle travel to work (84%) and the second lowest proportion of people walking to work (2.9%)–something that is being combated by the South Australian government in an effort to increase citizen ridership and use of public transport. Roads Road transport in Adelaide has historically been comparatively easier than many of the other Australian cities, with a well-defined city layout and wide multiple-lane roads from the beginning of its development. Adelaide has been called a "twenty-minute city", with commuters having been able to travel from metropolitan outskirts to the city proper in twenty minutes or less. However, the Royal Automobile Association now considers these roads are inadequate to cope with Adelaide's growing road traffic volumes. In 1964 the 'M.A.T.S.' plan (Metropolitan Adelaide Transport Study) was commissioned by the Government of South Australia. It examined establishing a large network of highways along Adelaide's main urban transport corridors. The plan went as far as the State Government of the day purchasing land along Adelaide's major roads, in preparation for highway construction. However, later State Governments abandoned the plan during the 1970s. The consequences of the political rejection of this plan are now being realised as increased traffic has caused travel times to increase, and congestion on main thoroughfares such as South Road has become a daily reality. Adelaide is connected to Port Wakefield Road and the Sturt Highway in the north, and the South Eastern Freeway in the South East. The Southern Expressway acts as a bypass for congested South Road in the southern suburbs of Adelaide. Bus The focus of Adelaide's public transport system is the large fleet of diesel and natural gas powered buses. The majority of services terminate at the city-centre or at a suburban interchange. Buses get priority on many roads and