Before Modern Engineering: How a Deadly Construction Mistake Led to NYC's Great Subway Cave-In of 1915

On the morning of September 22, 1915, New York City was in the middle of a massive expansion of its subway system. Workers were digging a new tunnel for the Broadway-Seventh Avenue line deep beneath the street. Above them, the city was moving through its morning rush hour, completely unaware of the structural failure happening below.

A Street Disappears

Just after 8:00 AM, a section of Seventh Avenue between 24th and 25th Streets suddenly gave way. The ground opened up, creating a massive crater that was 200 feet long and nearly the full width of the street. The collapse happened in an instant.

A crowded southbound streetcar, filled with passengers on their way to work, plunged directly into the pit. It fell more than 30 feet to the bottom of the subway excavation, landing on its side amidst a tangle of steel beams and splintered timber supports. A large truck from a local brewery also fell into the hole, along with tons of rock, dirt, and pavement. The air filled with dust and the sounds of twisting metal.

Rescue Amid the Wreckage

The scene was one of total chaos. The giant hole had severed gas mains and water lines, which began to flood the bottom of the pit. Police, firefighters, and construction workers who had been digging the tunnel immediately rushed to the edge of the crater to help.

Rescuers climbed down makeshift ladders into the unstable hole. They worked to pull survivors from the wreckage of the streetcar and the brewery truck. The rescue efforts were dangerous, as the sides of the crater threatened to collapse further. In total, the cave-in killed seven people and injured more than one hundred others.

The Cause of the Collapse

An investigation determined the direct cause of the disaster. The tunnel was being built using a method called “cut-and-cover.” Workers would dig a trench, build the subway tunnel, and then cover it back up. To keep the street active during construction, the road surface was held up by a temporary structure of heavy wooden beams.

Early that morning, workers deep in the tunnel had detonated a dynamite charge to clear rock. The blast was stronger than intended and it weakened the timber supports holding up the street above. The enormous weight of the fully loaded streetcar passing over the compromised section was the final trigger, causing the entire structure to fail.