The primary reason for the initial adoption of conduit systems was for aesthetic reasons as an alternative to overhead wiring that was often objected to as being unsightly. 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. The huge cost of building new conduits gave New York the distinction of having one of the last horsecar lines (the Bleecker Street Line) in the U.S., not closing until 1917. (Pittsburgh ran the last U.S. horsecar, in 1923.) In some old photographs, two "slots" may be seen between the rails. In New York City, sometimes one slot was used for a cable line and the other for electric cars. Occasionally, two competing lines shared a common track and had independent slots for the ploughs of the respective cars. In London, two slots were sometimes used on a single-track stretch in a narrow road so that cars in each direction used separate conduits. Known as twin-conduit track, examples were found in York Road, Wandsworth and London Street, Greenwich. In New York City, the Queensboro Bridge between Manhattan and Queens had tracks installed on the outer lanes with conduits for Manhattan cars in addition to overhead wires. The conduit allowed them to run to Queens Plaza terminus without need for removing the plough and raising the poles. In later years the conduit was removed and only trolley wire remained. In London, the London County Council Tramways experimented with side conduit, where the conduit was in one of the side rails. This was tried along Kingsland Road between Bentley Road and Basing Place, Hoxton, but the stresses and strains of the weight of the cars weakened the conduit, so it was not tried elsewhere. In the centre of Brussels some tram lines were fitted with conduits, the last ones being converted to overhead operation during World War II. The system was tried in the seaside resort of Blackpool, UK, but was soon abandoned as sand and saltwater entered the conduit and caused breakdowns and there was a problem with voltage drop. Some sections of track still had the conduit slot visible until the tramway was refurbished in 2012. Hybrid installations Washington, D.C. had a large network of conduit lines, to avoid wires. Some lines used overhead wires when they approached rural or suburban areas. The last such line ran