The secret world behind New York City's subway, which millions of people use every day

Photo: Mario Tama/Getty Images

The New York City subway system is one of the most iconic in the world, servicing over five million people every weekday. But its also been mired in budget problems, and some parts of its technology have remained largely unchanged since its inception in 1904.

The combination of these two things makes working on the subway quite the task for the Metropolitan Transportation Authority (MTA). And the MTA’s Instagram does a good job of showing what it’s like, taking you behind the scenes of flooded tunnels, snowy tracks, and welding jobs.

Here are 24 photos that show what it takes to keep one of the world’s biggest subway systems running:

Additional reporting by Graham Rapier.

'Crews are preparing to scrape old paint off the tunnel ceiling at 59 Street on the 4/5 lines...'

'There wasn't a cloud in the sky, so MTA New York City Transit had to bring in their own water to perform a 'wet test' of the flood barrier protection at the Bowling Green Station in Lower Manhattan.'

'Here, an old section of the third rail is hoisted up onto a work train near Classon Av...'

'...Silt can rapidly accumulate and reduce our ability to handle the approximately 13 million gallons-per-day we pump out. So, we have to get in there with a suction hose and a shovel to keep things flowing, ultimately preventing a flood in the subway system.'

'Signal maintainers were out performing maintenance on the vital junction at Broadway & Myrtle Av today where the J/M/Z lines diverge in Brooklyn.'

'The City of New York Board of Transportation was abolished in 1953, replaced by the New York City Transit Authority.'

'TurnStyle, a collection of shops and restaurants, opens in the concourse of 59 St-Columbus Circle...'

'Infrastructure crew grouts leaks in the tunnel ceiling under Broadway north of 157 St on the 1 line...'

'Here, track workers move in to hoist some of the 35 lengths of rail that were replaced this week during overnight FASTRACK work on the B/D/F/M lines in Manhattan.'

'Here, north of Bowling Green, with a dramatic flash of light and puff of smoke, molten steel flows into the a rail joint by the thermite welding process.'

'A Signal Maintainer clears snow from a stop arm on the West End line in Brooklyn.'

'A pop-up jazz concert was held on Sun., November 29, 2015 to commemorate the 100th anniversary of the birth of 'Take the A Train' composer Billy Strayhorn.'

'Detail from the former Brooklyn Rapid Transit's WWI memorial, located alongside the East New York bus depot.'

'Bus Maintainers at work in the Charleston Depot, Staten Island...'

'A member of Track Department cuts down a length of new rail to the correct size north of Chambers St on the 7th Ave 1/2/3 line...'

'Welding sections of a new third rail along the R line in Bay Ridge overnight...'

'A giant fan is deployed aboard a work train to alleviate the dust that's kicked up when the ballast tamper evens out the roadbed.'

'Crews worked through the night at 14 St. on the 1/2/3 lines after a water main break in the street.'

'Cleaners give a good scrubbing to the historic terra cotta reliefs in the Boro Hall station during overnight FASTRACK work on the Lexington Avenue line.'

'Adam Meagher surprised his girlfriend, Carolyn Grossman ... with a marriage proposal the middle of the Second Avenue Subway! The two are urban planners.'

'Jamie Benson performing in 'Party To-Go.''

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