Hard Rock

To finish up the brief dive into the construction of the original IRT subway, here are 1902 and 1903 photos titled “Central Park Tunnel.”

The title may seem a little weird, as the IRT subway – now the 1, 2, 3, 4, 5, 6, and 7 trains, has no stops in the park. But the plan was always to have two branches in upper Manhattan: one following Broadway and one serving central Harlem by running up Lenox Avenue (now Malcolm X Boulevard). The canonical “original IRT” from City Hall to 145th Street only operated for a month in the fall of 1904 before the Lenox Avenue branch opened.

The Lenox line branches off the Broadway line in the middle of the 103rd Street station: the two express tracks at 96th Street sink below the level of the local tracks as you head north, allowing them to curve east under 104th Street. After crossing Central Park West (Eighth Avenue) and entering the park, the tracks turn northeast, run under the Great Hill, just west of the Harlem Meer, and then turn left at Central Park North (110th Street) to run up Malcolm X. So there’s the Central Park Tunnel: less than half a mile long, cutting the northwest corner of the park.

The second picture above gives a pretty good sense of the bedrock below the hill. The first picture shows the wood formwork used to cast the concrete liner you see in the second picture. Where the tunnel structure had to support all the weight above – such as in the river tunnels – the IRT used the cast-iron liner segments popular everywhere at the time. Rock provides arching action, so the concrete was not particularly structural as much as it was a liner supporting waterproofing.