the second branch would turn eastward under Park Place and Beekman Street and down William Street and Old Slip. After going through Lower Manhattan, the second branch would go through a tunnel under the East River before running under Clark and Fulton Streets until a junction at Borough Hall with the existing Contract 2 IRT Brooklyn Line. In order to pass under the Broadway and Park Row subway lines, this branch has grades as steep as 3%, being located below surface level. As a result, the Park Place station was built with escalators. Because William Street is so narrow ( wide), every building along the line had to be underpinned. The entire line, consisting of eight sections, was expected to cost $14,793,419. On September 22, 1915, there was an explosion during construction of the 23rd Street subway station that caused the tunnel to collapse. Seven people were killed after a blast of dynamite in the subway tunnel destroyed the plank roadway over Seventh Avenue. As a result, a crowded trolley car, and a brewery truck fell into the excavation, accounting for most of the injuries. Opening On June 3, 1917, the first portion of the Broadway–Seventh Avenue Line south of Times Square–42nd Street, a shuttle to 34th Street–Penn Station, opened; a separate shuttle service, running between 42nd and 34th Streets, was created. This short extension was opened even though the rest of the route was not yet completed in order to handle the mass of traffic to and from Pennsylvania Station. Only the northern part of the station was opened at this time, and piles of plaster, rails, and debris could be seen on the rest of the platforms. On June 27, 1918, the Public Service Commission (PSC) announced that on July 1, the shuttle would be extended south to South Ferry, with a shorter shuttle on the Brooklyn branch between Chambers Street and Wall Street, on July 1, 1918. The PSC's decision to open the line before the Lexington Avenue Line was completed was unexpected. The new "H" system was implemented on August 1, 1918, joining the two halves of the Broadway–Seventh Avenue Line and sending all West Side trains south from Times Square. An immediate result of the switch was the need to transfer using the 42nd Street Shuttle. The completion of the "H" system doubled the capacity of the IRT system. The local tracks ran to South