A railway electrification system supplies electric power to railway trains and trams without an on-board prime mover or local fuel supply.
Electrification has many advantages but requires significant capital expenditure.
Selection of an electrification system is based on economics of energy supply, maintenance, and capital cost compared to the revenue obtained for freight and passenger traffic.
Different systems are used for urban and intercity areas; some electric locomotives can switch to different supply voltages to allow flexibility in operation.
This is a model of a London Underground or ‘tube’ train.
The London Underground is a public rapid transit system serving a large part of Greater London and parts of the home counties, and is considered the oldest rapid transit system, incorporating the world’s first underground railway, the Metropolitan Railway, which opened in 1863 and is now part of the Circle, Hammersmith & City and Metropolitan lines.
It was also the first line to operate underground electric traction trains, the City & South London Railway in 1890, now part of the Northern Line.