London Underground Infrastructure

London Underground Infrastructure

The infrastructure of the London Underground includes 11 lines, with 270 stations. Lines on the Underground can be classified into two types, subsurface and deep-level or tube. Lines of both types usually emerge onto the surface outside the central area. While the tube lines are for the most part self-contained, the subsurface lines are part of an interconnected network. The Underground uses rolling stock built between 1960 and 2005. The Underground is one of the few networks in the world that uses a four-rail system. The additional rail carries the electrical return that on third-rail and overhead networks is provided by the running rails. Planned improvements include new stations, line extensions, computerised signalling, automatic train operation (ATO), track replacement, new rolling stock, new cooling systems, and mobile phone coverage underground.