Line 4 is a rapid transit line of the Madrid Metro connecting the west and center of Madrid with the said city's northeastern end, running between Argüelles and Pinar de Chamartín. It consists of a total of 23 narrow-gauge stations with 60-metre platforms. Altogether, its route measures just under 15 kilometers, with a journey that lasts approximately 38 minutes. It is operated by a single train model, the 3000 series of the CAF company, which circulates in compositions of 4 cars. This represents a limitation on its maximum passenger capacity per train, which is compensated by one of the highest frequencies in the entire network.

The Madrid Metro is a rapid transit system serving the city of Madrid, capital of Spain. The system is the 14th longest rapid transit system in the world, with a total length of 293 km (182 mi). Its growth between 1995 and 2007 put it among the fastest-growing networks in the world at the time. However, the European debt crisis greatly slowed expansion plans, with many projects being postponed and canceled. Unlike normal Spanish road and rail traffic, which drive on the right, Madrid Metro trains use left-hand running on all lines because traffic in Madrid drove on the left until 1924, five years after the system started operating.