Line 6 (Madrid Metro)

Line 6 (Línea 6 Circular) of the Madrid Metro opened originally between Cuatro Caminos and Pacifico in 1979. This is one of two circular lines in Madrid, but unlike Line 12, it did not open as a full circle. The circle was completed in 1995, taking four stages from its original opening. It has a length of 23.5 km and is coloured grey on route maps.

The line is made up of 28 stations with 115-metre platforms, linked by 23.472 km of wide gauge tunnel tracks. It allows one to transfer twice to all the lines of the network (three times in the case of lines 3 and 4) with the exception of lines 8 and 11, which start from the circular route and do not enter it, and the peripheral lines. (such as line 12 and the Light Metro lines).

Being built to allow transfers with many other lines and to cover the entire central area of the city, plagued by unevenness, it is one of the first lines, along with line 5, that was built at great depth, so that it would not suffer major damage from unevenness in its route. Thus, for example, the greatest depth of the Madrid Metro system is reached at the Cuatro Caminos station (a depth of 45 meters below ground) given that the tunnel is at the same altitude above sea level as, for example, in Príncipe Pío, its most superficial point (where it still remains two stories below the ground). This means that although the line is of very high utility in the system, sometimes some of the transfers are longer than the average in the network.

Along its route are some of the large interchanges built in recent years: Moncloa, Príncipe Pío, Plaza Elíptica and Avenida de América, in addition to the correspondence with Cercanías Renfe in Nuevos Ministerios, Laguna and Méndez Álvaro (which also coincides with the South Bus Station of Madrid).

History
First on 7 May 1981, the line was extended from Pacifico to Oporto, then on 1 June 1983, the line was extended from Oporto to Laguna. Thirdly the line was extended from Cuatro Caminos to Ciudad Universitaria serving Madrid's Complutense university on 13 January 1987, and lastly the line was extended from Ciudad Universitaria to Laguna on 10 May 1995, completing the circle. Arganzuela-Planetario station opened on 26 January 2007 between Legazpi and Méndez Álvaro. This station serves Madrid's Planetarium and IMAX theatre.

Operation
Line 6 is one of the busiest lines on the network, so to ease congestion on the busiest stations, Madrid adopted the "Spanish solution". This means that at some stations there are two side platforms, and an island platform. This was also used on Line 5, but only two stations preserve the original layout (Campamento and Carabanchel). Line 6 uses 6-car trains of mostly class 8400, however the line still has class 5000s on the line.

Trains travelling clockwise (when viewing the route map from above) are designated as "Platform 2" (Andén 2), while those travelling anticlockwise are designated as "Platform 1" (Andén 1).