Hybrid Installations
Washington, D.C. 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. The current collector "plow" as it was called, was mounted underneath the car on a fitting just forward of the rear truck on D.C. Transit's PCC cars. It had two cables with female connectors on cables to attach to matching cables of the car's electrical system. A "plowman" was assigned at each changeover point from overhead trolley wire to conduit point to remove the cable attachments to the car and stow the plow, which would not remain with the car, but which would be reattached in an incoming car running on overhead wire. The lower section of the plow "board" was drawn by the moving car above within the cavity of the conduit. 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. The 'pit' here has the meaning analogous to racing circuit pits rather than a depression in the road.
In the UK, London also 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 from conduit to overhead wire (at what was known as the 'change pit') the change process was largely automatic. The conductor released the trolley pole onto the wire then, as the tram moved forward, the conduit channel veered sideways to outside the running track automatically ejecting the collector plough. The tram was said to be 'shooting the plough'. At the change-over between overhead wire and conduit, the process was a little more complicated. The tram pulled up alongside a ploughman who engaged a two-pronged guide (known as a 'plough fork') over the plough in a short length of unelectrified conduit and into the plough channel underneath the centre of the tram. As the tram drew forward, the conduit channel moved under the tram carrying the plough into position. The conductor could then pull down the trolley pole and stow it. The process is illustrated here. The ploughman's job was a fairly skilled one because, if he failed to locate the plough fork correctly, it or the plough itself could jam in the plough channel and cause lengthy delays. Some tram designs required an extra carrier to be located with the plough and these frequently caused problems for ploughmen not used to the design (particularly if the tram had been diverted from its normal route).
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 June 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, Nice, Lyon, Lille 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.
Read more about this topic: Conduit Current Collection