Conduit current collection

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Conduit current collection was a system of current collection used by electric trams where the power supply was located in a channel under the roadway, rather than located overhead.

1 Description
2 Usage
3 Hybrid installations
4 See also
5 External links

[edit] Description

The power rails for conduit cars are contained in a vault between and underneath the running rails, much in the same fashion as the cable for cable cars. The vault contains two "T" section steel power rails of opposite polarity facing each other, about 12 inches apart and about 18 inches below the street surface. Power reached the car by means of an attachment beneath the streetcar that rode in the conduit, called a plow (US), plough (British). The plow had two metal shoes that pushed sideways against the power rails, and connected to the car's controller and motor(s). The running rails are not part of the electrical circuit. In America the cars were sometimes popularly but incorrectly called trolleys, but did not typically draw power from overhead wire, as trolleys do.

[edit] Usage

The world's second electrically operated street railway was in Denver, Colorado, starting in 1885. It pioneered the use of conduit current collection. Difficulties with the conduit and the electric streetcars led to the replacement of all conduit cars and lines with cable cars by 1888.

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

In the centre of Brussels, a number of tram lines were fitted with conduit, the last ones being converted to overhead operation during World War II.

[edit] Hybrid installations

Washington, D.C., also had a large network of conduit lines, to save the capital city from unsightly wires. Some lines used overhead wires when they approached rural or suburban areas. The last such line ran to Cabin John, Maryland. Because of this usage, many of 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 a hybrid network of double-deck trams: overhead collection was used in the outer sections and conduit in the centre. At the change-over points between the overhead wire and the conduit, the trolley pole was hooked down and a plough (as the device to collect the current from the conduit was known) was introduced under the vehicle from a stock kept at the side of the road. The method was to shove the plough as hard as possible along a short stretch of unelectrified conduit which diverged towards the side of the road, so that momentum drove it into place. The process is illustrated here.

New track was laid as late as 1951 for the Festival of Britain, which commemorated the Great Exhibition of 1851. The last tram was withdrawn in 1952 and virtually all the tracks had been removed by the 1970s, although a short section can still be seen in the Holborn area at the entrance to the former Kingsway Tramway Subway.

Other European hybrid tramway networks included Paris and Bordeaux in France, Berlin, Vienna and Budapest. In Paris the conduit sections were frequently very short, requiring cars to change from overhead to conduit and back several times in one journey. The last conduit line in Paris closed in 1936, while the last Bordeaux conduit car ran in 1953. The conduit systems in Berlin, Vienna and Budapest were very short-lived. All three were replaced by overhead working before World War I.