Line 4 (Madrid Metro)
Line 4 is a line of the Madrid Metro with 23 stations. Originally opened in 1944, the station has been expanded many times over the years and is now one of the busiest lines in the Madrid metro.
The Line 4 was opened on 23 March 1944 between Goya and Argüelles. 
In 1958, the line took up a branch of line 2 from Goya to Diego de León, which originally opened on 17 September 1932. In the 1970s, the line was extended in two stages: from Diego de León to Alfonso XIII (1973) and from Alfonso XIII to Esperanza (1979). On 1 April 1998, the line was extended from Esperanza to Mar de Cristal, to provide interchange with the new Line 8. Later that year on 15 December, the line was extended to Parque de Santa María. On 11 April 2007, an extension from Parque de Santa María to Pinar de Chamartin opened. At Pinar de Chamartin, interchange with Line 1 can be made and from spring 2007, interchange with Metro Ligero 1 (ML1) is available too. At Pinar de Chamartin, an island platform is used for departures, and a side platform for arrivals. Line 4 has used four-car trains of class 3400 since 2007.
- "El ministerio de obras publicas preside la inauguracion de la obra nueva linea del metro". ABC (in Spanish). Madrid, Spain. 24 March 1944. Retrieved 17 November 2017.
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- Madrid Metro (official website)
- Schematic map of the Metro network – from the official site (in English)
- Madrid at UrbanRail.net
- ENGLISH User guide, ticket types, airport supplement and timings
- Network map (real-distance)
- Madrid Metro Map