The Hamburg S-Bahn is a rapid transit railway system in the Hamburg Metropolitan Region. Together, the S-Bahn, the Hamburg U-Bahn, the AKN railway and the regional railway form the backbone of railway public transport in the city and the surrounding area. The network has operated since 1907 as a commuter rail system, under the direction of the state railway, and is a member of the Hamburger Verkehrsverbund. There are four lines, serving 68 stations, on 147 kilometres (91 mi) of route. On an average working day the S-Bahn transports about 590,000 passengers; in 2010 about 221 million people used the S-Bahn.