All of the system runs on 630 volts DC, with the -210 volt negative rail between the running rails and the +420 volt positive rail outside the running rails. The positive rail can be on either side of the track but is positioned furthest from the platform at stations. read more
Nicholas Stone, lives in London (1993-present) and Quora User, Train Driver at London Underground (1989-present) · Author has 66 answers and 29.6k answer views All of the system runs on 630 volts DC, with the -210 volt negative rail between the running rails and the +420 volt positive rail outside the running rails. read more
This map shows all trains (yellow dots) on the London Underground network in approximately real time. Skyfall version I have similar things for the London buses and National Rail, and an awesome bookmarkable train times journey planner. read more
Serena: On the London Underground both the central rail AND the outer rail are live. The system used there is known as 4th rail and runs at a nominal 660V DC with just over 400V DC running in the central rail in one direction and at just over 200V DC in the outer rail in the opposite direction. read more