Plans to build a rapid transit system in New York were first made in 1831. By 1868 the first elevated railway was erected. As the "El" became crowded, construction of an underground railway was proposed. Ground was broken on March 24, 1900. The original subway, which took opened October 27, 1904, ran 9.1 miles from City Hall to 145th Street and Broadway. The fare was a nickel. Extensions to the Bronx opened in 1905 and to Brooklyn in 1908, completing the first subway. Today, the rapid transit system in New York is one of the largest in the world, with a fleet of 7,000 cars making 8,000 trips daily. In building such a system, unusual engineering challenges had to be overcome: above the streets were towering buildings and heavy railway and vehicular traffic; under the streets was a complicated network of subsurface structures -- sewers, water and gas mains, conduits for electric cables, electric surface railway systems, telegraph and power lines, and numerous basement vaults. Other contributions included innovative practices in cut-and-cover excavations, subaqueous shields, rock tunneling, steel bent construction, etc.