system. There is a debate around the origin of the name "S-tog" ("S-train") with many citing that the name of the system came from a competition in the newspaper Politiken . The judges' panel cited a long list of possible explanations for the "S" in S-tog, including: "state railways", "city railway", "Greater Copenhagen", "sun", "lake", "forest", "beach", "snow", "skiing", "skating", "sleigh", all of which start with an S in Danish. Larsen and Poulsen, however, challenge that this basis for the system name as an urban myth and that DSB had already determined the name. The names, though, demonstrate that the initial marketing of the S-trains emphasized recreational day trips from the city to the countryside. Hellerup to Hillerød, Svanemøllen to Farum were existing lines reorganized into the new network as was the line between Frederikssund and Valby. The section Valby – Vanløse opened in 1941, was extended to Ballerup in 1949 and then finally to Frederikssund in 1989. The system had single tracks between Ballerup and Veksø until 2000 and between Veksø and Frederikssund until 2002. New tracks were established along the existing Valby – Høje Taastrup line between Valby – Glostrup, opening in 1953. It was extended to Taastrup in 1963 and then 1986 to its final destination at Høje Taastrup. A completely new line: The Køge Bay line was built between Dybbølsbro and Køge in four stages: Dybbølsbro – Vallensbæk opened in 1972; Vallensbæk to Hundige in 1976; Hundige to Solrød Strand in 1979 and then finally to Køge in 1983. The Frederiksberg – Vanløse – Grøndal line was closed with the arrival of the Copenhagen metro. The former Godsbaneringen Grøndal – Ny Ellebjerg route has been converted to an S-line. Originally, no letters or numbers were used for the individual lines, but with the introduction of the summer timetable on 14 May 1950 the system moved to line letters. The S-train system has been entirely one-man operated since 1978. Network The network consists of a central section through downtown Copenhagen that splits into three radial lines at each end, reaching the outer suburbs and neighbouring towns. The radial sections are connected to each other via that central section. The system is designed so that a train from any southern radial can continue along any of the three northern and vice versa. In the city centre, the trains run underground in two tunnel sections which are also served