Railway electrification system

The main advantage of electric traction is a higher power-to-weight ratio than methods such as diesel or steam that generate power on board. This enables faster acceleration and higher tractive effort on steep grades. On locomotives equipped with regenerative braking, descending steep grades requires little use of air brakes as the locomotive's traction motors become generators sending current back into the supply system and/or on-board resistors (which convert the excess energy to heat).

Other advantages include the lack of exhaust fumes at point of use, less noise and lower maintenance requirements of the traction units. Given sufficient traffic density electric trains produce fewer carbon emissions than diesel trains, especially in countries where electricity comes primarily from non-fossil sources, such as Austria and France.

A fully electrified railway would have no need to switch between methods of traction thereby making operations more efficient. One country that approaches this ideal is Switzerland.
The main disadvantage is the capital cost of the electrification equipment, most significantly for long distance lines that do not generate heavy traffic. Suburban railways with closely-spaced stations and high traffic density are the most likely to be electrified, and main lines carrying heavy and frequent traffic are also electrified in many countries