Public transport is well-developed with bus (), tram () and trolleybus () lines running in all areas of the city. The Sofia Metro became operational in 1998, and now has four lines and 47 stations. , the system has  of track. Six new stations were opened in 2009, two more in April 2012, and eleven more in August 2012. In 2015 seven new stations were opened and the underground extended to Sofia Airport on its Northern branch and to Business Park Sofia on its Southern branch. In July 2016 the Vitosha Metro Station was opened on the M2 main line. A third line was opened in August of 2020 and re-organisation of the previous lines lead to a 4th line being created. This line will complete the proposed underground system of three lines with about  of lines. The master plan for the Sofia Metro includes three lines with a total of 63 stations. Marshrutkas provide an efficient and popular means of transport by being faster than public transport, but cheaper than taxis. There are around 13,000 taxi cabs operating in the city. Additionally, all-electric vehicles are available through carsharing company Spark, which is set to increase its fleet to 300 cars by mid-2019.