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A series of recent manhole fires in the heart of Manhattan forced the evacuation of several theaters and was a stark reminder that the subway is not the only creaky infrastructure beneath the streets of New York City.

Underground lies a chaotic assemblage of utilities that, much like the subway, are lifelines for the city: a sprawling tangle of water mains, power cables, gas and steam lines, telecom wires and sewers.

The city has one of the oldest and largest networks of subterranean infrastructure in the world, with some portions dating more than a century and prone to leaks and cracks.

And winter — from the corrosive rock salt used on streets and sidewalks to “freeze-thaw” cycles that weaken pipes — makes infrastructure problems even worse.