In 1895 electric traction, which previously had proved successful on street railways, was introduced on short sections of U.S. railroads, which were then powered by steam-driven locomotives. This innovation was adopted first by the New York, New Haven, and Hartford Railroad and later in the same year by the Pennsylvania Railroad and the Baltimore & Ohio Railroad. At first electric power was used principally in urban areas and especially in tunnels, to eliminate smoke and steam.
The electrification of the tracks passing under Park Avenue to enter Grand Central Terminal in New York City was in response to a serious accident that had occurred when the tunnel became filled with smoke. This electrification project, completed in 1907, was undertaken in compliance with a state law requiring railroads to discontinue the use of combustion engines within New York City.
Later, the value of electric traction in mountainous regions was discovered. Electricity provides greater power on grades than can be achieved with steam, and the use of regenerative braking, in which the motor functions as a generator on downgrades, makes for greater safety and also for economy, because the power produced on downgrades is fed into the supply line.
Some of the most extensive electrification in the United States was done by the Pennsylvania Railroad on approximately 1,080 km (670 mi) of route, with about 3,620 km (2,250 mi) of track, connecting New York City, Philadelphia, and Washington, D.C., and extending westward to Harrisburg, Pennsylvania. An important consideration underlying the adoption of electric traction in this densely populated area was the need for increased carrying capacity. Because electric locomotives can accelerate more rapidly, faster schedules could be established and more trains could be run on the same track.
In installations made early in the 20th century in the suburbs of New York City, power is distributed by means of a third rail. This method is still used on some railroads, although it limits power to 600 volts and live rail is dangerous. Today, on more than 95 percent of electrified railroads in the world, current is collected from overhead wires. The circuit is completed through the running rails, which must be grounded.
While electric railroads are popular throughout the world, they are less so in the United States. In the 1950s the Great Northern Railroad (now Burlington Northern Santa Fe) removed its electric wires that crossed the Cascade Mountains. Several other major railroads followed suit in the mid-1970s. In 1981 Conrail (which has subsequently been bought by CSX and Norfolk Southern) put its electric freight-train locomotives into storage. Electric train operation became relegated to short utility-owned private railroads, intercity and suburban passenger trains, and subways.