Merseyrail is a commuter rail network which serves Merseyside and adjacent areas of Cheshire and Lancashire. Merseyrail serves 69 stations across two lines – the Northern Line and the Wirral Line. The network uses 750 V DC third rail electrified lines having 75.0 miles (120.7 km) of routes, of which 6.5 miles (10.5 km) are underground. Merseyrail was established in 1977, when existing railway lines were connected by constructing new tunnels under Liverpool city centre and Birkenhead. The nucleus of the system was the Mersey Railway, which opened from Liverpool James Street to Green Lane, Birkenhead, running through the 1886 Mersey Railway Tunnel. This line is the world's oldest underground railway outside London.