were upgraded and subsequently re-opened in 2011 and 2014, respectively. Following the upgrade, all T1000 stock can be retired and replaced by the new MX3000 trains. The Grorud and Lambertseter Lines serve the Groruddalen valley while the Østensjø and Lambertseter Line serve the southern areas of Nordstrand. These four lines have the highest ridership. In the west, the Kolsås, Røa, Holmenkoll and Sognsvann Lines serves less densely populated areas. The Ring Line serves the northern borough of Nordre Aker, while the Common Tunnel serves the city center. List The following table presents the eleven lines of the Oslo Metro. They are chronologically sorted by the date of the first section of line to open. The service column indicates which of the six numbered services operates on most of the lines. Services are omitted from lines where they serve only one or two stations. The date indicates the official opening date of the line on the section noted in the fourth column. Sections with blue background indicate lines that were opened as tramways, while white background indicates the line was converted to or built as metro standard. The length column indicates the total length of the line at the time of opening or upgrade, and the extension column indicates the length of the extension. The station column indicates the number of stations on the line after the opening of each extension or upgrade. Unless specified otherwise, the lines are metro standard. References Notes Bibliography