With an estimated cost of SEK 16.8 billion (January 2007 price level), which equals 2.44 billion US dollars, the City Line, an environmentally certified project, comprises a -long commuter train tunnel (in rock and water) beneath Stockholm, with two new stations (Stockholm City and Stockholm Odenplan), and a -long railway bridge at Årsta. The City Line was built by the Swedish Transport Administration in co-operation with the City of Stockholm, Stockholm County Council, and Stockholm Transport, SL. As Stockholm Central Station is overloaded, the purpose of this project was to double the city's track capacity and improve service efficiency. Operations began in July 2017.