Muni began service on December 28, 1912, when the A Geary-Park line was inaugurated, running between the Financial District and the Richmond District on the western side of the city. The streetcar system was expanded over the next 16 years, including the Twin Peaks Tunnel in 1918 and the Sunset Tunnel in 1928. Muni began operating buses in 1917, and trolleybuses in 1941. The city acquired the competing Market Street Railway in 1944, doubling the size of Muni; its purchase of the bankrupt California Street Cable Railroad in 1952 made it the city's sole transit operator. Replacement of streetcars by buses in the 1940s and 1950s left only five streetcar lines; they were converted to Muni Metro light rail in 1980 with the completion of the Market Street subway. Numerous services changes over the lifetime of Muni gave rise to the lines in use today; a number of other lines have been discontinued.