Until 1958, trams formed a network spanning most of Adelaide, with a history dating back to 1878. Adelaide ran horse trams from 1878 to 1914 and electric trams from 1909, but has primarily relied on buses for public transport since the mid-20th century. Electric trams, and later trolleybuses, were Adelaide's main method of public transport throughout the life of the electric tram network. The tram network was progressively closed down through the 1950s with the last lines closing in 1958; the Glenelg tram line was the only line to survive these closures and has remained in operation ever since and has been progressively upgraded and extended since 2005.