Electrification of rail lines is one of the most significant

Electrification of rail lines is one of the most significant and transformative changes railroading has ever experienced. Its benefits are numerous, including reduced operating costs and improved speed of service. However, the implementation capital is substantial and carries with it some risks. Historically, a combination of factors has made electrification a challenge to implement, with a result that only a few major railways have implemented it on large scales.

The most common type of electrification is through power rails, which supply traction current for electric locomotives and other equipment. These rails are normally made of high-conductivity steel bolted to aluminium to improve conductivity, with a stainless steel contact surface or cap for added durability. This system is used on the Montreal Metro, Paris Metro, Santiago Metro, Sapporo Municipal Subway and other similar systems, as well as on rubber tyred transit trains such as those of the Hong Kong Mass Transit Authority.

In addition to the power rails, some systems have a third rail for distributing electrical signals to control operations of trains. The third rail is typically a separate metal contact block, which can be switched to power or coast modes by the train operator. The third rail can also be used to supply electricity for platform lighting and announcements. The rails are usually insulated from the running rails, although in some cases this is not the case.

Some of the earliest electric railways were powered by a central third rail, such as Volk's Electric Railway in Brighton, England, which opened in 1879, and the Giant's Causeway Tramway in Ireland, which began operation in 1883. This system was also used on some early urban electric railways, such as the London Underground's surface lines. A heavy "shoe" suspended from a beam attached to the train's bogies slides over the third rail to collect its power, with the positive rail having twice the voltage of the negative.

An overhead wire is another form of electric railway electrification, which is most commonly used in suburban commuter systems and on modern rapid transit systems such as the New York City Metro. It is also used on some main line passenger railroads, such as the Long Island Rail Road's CSX-Westinghouse Electric-powered Brooklyn, Queens and Rockaway Line, which has its own overhead power towers.

When a train is stopped at a station, it's important to stay away from the third rail. It can carry up to 650 volts of direct current, enough to kill a person within five seconds of contact. To prevent shock, the third rail is usually covered or protected by a platform screen, but even when this is in place it's still possible to be electrocuted by touching the rail. The best way to avoid this is to run away as quickly as possible from the platform when a train is approaching.