A conduit car was an electric streetcar (tram) that drew power from an underground third rail, rather than from overhead wire, a wayside energized rail, or an on-board battery.

Description

The third rail for conduit cars was contained in a vault between and underneath the running rails, much in the same fashion as the cable for cable cars. Power reached the car itself by means of an attachment beneath the streetcar that rode on top of the third rail called a plow. The cars were sometimes popularly but incorrectly called trolleys, but did not typically draw power from overhead wire, as a trolley would.

Usage

New York City had the largest installation of conduit cars due to the prohibition of stringing overhead wires on Manhattan Island, although a few Bronx-based trolley lines entered the northern reaches of Manhattan using overhead wire. Trolley lines from Brooklyn and Queens also entered Manhattan under wire, but did not use city streets.

The expense of creating conduit lines in New York was somewhat reduced where it was possible to convert the cable vaults from discontinued cable car lines to conduit use. The huge expense in building new conduit, however, gave New York the distinction of having the last horsecar lines in the U.S., not closing until 1914.

Paris had a conduit tramway network, or tram avec troisième rail in the 19th century, but it did not last long.

Hybrid installation

Washington, D.C. also had a large network of conduit lines, to save the capitol city from unsightly wires. In Washington's case, though, some lines used overhead wire when they approached rural or suburban areas. The last such line ran to Cabin John, Maryland. Because of this usage, Washington's streetcars carried trolley poles, which were lowered while operating in the central part of the city; when the cars reached a point where they switched to overhead operation, they stopped over a plow pit where the conduit plows were detached and the trolley poles raised, the reverse operation taking place on inbound runs.

London, England had an hybrid network of double decker tramways. New track was laid as late as 1951 for the Festival of Britain which commemorated the Great Exhibition of 1851. Operations stopped in the 1950s and the tracks were removed in the 1980s and 1990s. In the last decades of operations the increased motor traffic fell afoul of the conduits too many times.

Sealed conduits in the 21st century

New technologies exploiting the phenomenon of electromagnetic induction have made it possible to build tram systems with an underground third rail in a sealed conduit, in the middle of the way, between the two tracks. The city of Bordeaux, France was the first to exploit this in 2003 when it opened its new "ligne A". Teething problems with the seals and frequent water infiltration has led to frequent closure of the line.