Conduit current collection is an obsolete system of electric current collection used by some electric tramways, where the power supply was carried in a 'conduit' (a small tunnel) under the roadway. Modern systems fall under the term ground-level power supply. Description The power rails are contained in a conduit midway between and below the two surface rails on which the cars operate, in much the same fashion as the cable for cable cars. The conduit contains two "T" section steel power rails of opposite polarity facing each other, about apart and about below the street surface. Power reached the car by means of an attachment, called a plough (US plow), that rode in the conduit beneath the car. The plough had two metal shoes attached to springs that pushed sideways against the power rails. The plough was normally connected to a platform that could slide laterally to conform with variations in the placement of the conduit, for example in some areas there was a conduit for cable cars adjacent to the one for electric cars. The current was carried by a flexible cable from the plough through the platform to the car's controller and motor(s). The running rails are not part of the electrical circuit. In the United States, the cars were sometimes popularly but incorrectly called trolleys but did not typically draw power through a trolley pole from an overhead wire as (strictly defined) trolley cars do. Usage Conduit current collection was one of the first ways of supplying power to trams but it proved to be much more expensive, complicated and trouble-prone than overhead wires. When electric street railways became ubiquitous, it was only used in those cities that did not permit overhead wires, including London, Paris, Berlin, Marseilles, Vienna, Budapest, and Prague in Europe, and the New York City borough of Manhattan and Washington, D.C. in the United States. In Denver, Colorado, the world's second electric street railway in 1885 pioneered conduit current collection. Difficulties with the conduit and the streetcars led to the replacement of conduit cars and lines with cable cars by 1888. New York City had the largest installation of conduit cars, due to the prohibition of 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.