Electric trains are powered by electricity. Electric locomotives are powered by electricity from overhead lines, batteries or a supercapacitor. Electric locomotives benefit from the high efficiency of electric motors, often above 90% (not including the inefficiency of generating the electricity). Additional efficiency can be gained from regenerative braking, which allows kinetic energy to be recovered during braking to put power back on the line. Newer electric locomotives use AC motor-inverter drive systems that provide for regenerative braking. Electric locomotives are quiet compared to diesel locomotives since there is no engine and exhaust noise and less mechanical noise. The lack of reciprocating parts means electric locomotives are easier on the track, reducing track maintenance and power plant capacity is far greater than any individual locomotive uses. Electric locomotives can have a higher power output than diesel locomotives and they can produce even higher short-term surge power for fast acceleration. Electric locomotives are ideal for commuter rail service with frequent stops such as the Chicago South Shore & South Bend Railroad. Electric locomotives are used on freight routes with consistently high traffic volumes (common along the east coast), or in areas with advanced rail networks. Power plants, even if they burn fossil fuels, are far cleaner than mobile sources such as locomotive engines. 

As a child I remember traveling on the Chicago South Shore & South Bend Railroad, also known as the South Shore Line, and watching the overhead electrical lines (on the track along side) swaying in the wind. At the time I thought it odd that the wires didn't snap. The South Shore Line is the last of the remaining interurban electric trains in the United States. Running between Chicago, Illinois and South Bend Indiana, it is often times standing room only as daily travelers use it to commute back and forth to work.

An Electric train uses a device such as a pantograph, bow collector or trolley pole that connects to overhead wires (lines), pressing against the underside of the lowest overhead wire, known as the contact wire. Current collectors are electrically conductive and allow current to flow through to the train or tram and back to the feeder station through the steel wheels on one or both running rails.