NEW YORK CITY — When it's finally completed in 2016, New York City's Second Avenue Subway Line will be the culmination of 75 years worth of planning, millions of tons of extracted slag, and over $17 billion in spending. But that's not the point. What's important is that this long-awaited public transportation option will connect hundreds of thousands of people from Harlem to the Lower East Side. If New York City is the heart of the world, this route will certainly be one of its major arteries. Wired Science descended seven stories beneath Manhattan to uncover the tempestuous history of the line, speak with the men and women excavating it, and meet the literal spearhead of the project: an 800-foot long, two-story-tall tunnel-boring machine capable of chewing through 60 feet of subterranean rock every day. Photo: Jonathan Snyder/Wired.com

The need for a subway line under Second Avenue stupendously goes all the way back to 1919. At the conclusion of World War I, New York City’s Public Service Commission looked for a way to relieve mounting traffic and pedestrian congestion in Manhattan. City engineer Daniel L. Turner devised an ambitious plan that added subway routes beneath just about every Manhattan avenue running north to south along with lines that connected Queens, Brooklyn and Staten Island. The centerpiece of this plan was a gargantuan six-track line that ran underneath Second Avenue. Ten years after his proposal, the Board of Transportation greenlit a version of Turner’s complicated proposal that included his plan for a huge thoroughfare running along Second Avenue and earmarked $98,900,000 for it (over $1.2 billion in today’s dollars). But when the stock market plummeted and the economy imploded in October of that year, funding for the line evaporated. And it would become money, not technology or personnel or politics that would remain the line’s greatest hurdle for the next seven and a half decades. Above: Workers repair the massive iron struts that keep the launch box walls from collapsing. Photo: Jonathan Snyder/Wired.com

There would be other attempts through the years to jumpstart the project. A serious attempt was made in 1939 only to have the United States’ entry into World War II put the project on hiatus. More delays came because of astronomical increases in building material costs during the Korean War. Then a stagnant economy in the 1970s coupled with one of the worst financial crises in New York’s history, plus a mass population exodus to the suburbs, stalled production again. It wasn’t until the financial boom of the '90s in conjunction with an influx of people back into the city that the subway line under Second Avenue was finally seen not only as a real possibility, but also as a required necessity. In 2005 NYC voters passed a transportation bond that jumpstarted the project. Some $337 million was earmarked for the tunneling and the project finally got underway. Above: The control station of the tunnel-boring machine. Most operations are handled via a touchscreen interface. Photo: Jonathan Snyder/Wired.com

When the Second Avenue project was first conceived in the early 20th century, tunnel boring usually meant one thing: dynamite. And lots of it. At the time, safety precautions and explosives did not necessarily go hand in hand. In fact, during the construction of the Pennsylvania tunnels that run underneath the East and Hudson rivers, so many workers died (from explosives, cave-ins and other assorted hazards) that officials sent bodies to the Bronx and Brooklyn in the hopes of concealing their negligence. Eventually the story broke, and amid the turmoil, the workers united to form what is now known as the Local 147 — the same workers’ union (known as the sandhogs) that is handling the drilling today. And they still use dynamite. Above: Clockwise from top left: Local 15 mechanic Joseph Sammarco, electrician Alan Bates electrician, chief geologist Scott Chestman, wielder Wendell James. Photo: Jonathan Snyder/Wired.com

In 2007 ground was broken on 96th Street to create a launch box — a seven-story-deep, 1000-yard-long, and 75-foot-wide rectangle that would act as housing for the enormous tunnel-boring machine that would do most of the drilling for the line and would later be transformed into a subway station. Workers used a combination of high explosives and heavy machinery to carve out the launch box in a little under three years. But to create an ideal subway tunnel, you need to drill it with giant drills. That’s where the enormous tunnel-boring machines come in. This two-story-tall, one-million-pound, 800-foot-long machine is designed to bore through 20 yards of rock face in a single day. Above: The face of the boring machine contains 44 steel cutters and weighs 500 tons. Photo: Jonathan Snyder/Wired.com

The drill is placed on a track where an array of hydraulic pistons presses it forward. As the drill is applied to the rock, the steel discs on its face shred the stone in its path. The resulting debris, called slag, is collected through a set of channels on the drill’s face and ferried on conveyor belts to the rear of the machine. As more of the rock is drilled, the machine creeps forward along its track. Think of it like a giant earthworm. It’s not spectacular to see the drill spin — it moves at only about 5 rpm. But it is efficient. If workers used dynamite and conventional mining techniques, they would only be able to clear about half the stone the machine does in the same amount of time. Above: This conveyor belt will ferry the 50–60 feet worth of sledge (a mixture of rock, mud and water) that is excavated by the machines each day. Most of the sledge will be dumped in New Jersey. Photo: Jonathan Snyder/Wired.com

“The best part of this job is getting to see parts of the Earth no one has ever seen before,” said Scott Chestman, chief geologist for the Second Avenue subway construction. He spoke rapidly and lovingly of the stone that forms the foundation of his native New York City.> The rock under Manhattan is unique. Called Manhattan schist, it was forged some 470 million years ago during the formation of the supercontinent Pangaea. Unlike the rock beneath nearby Queens and Brooklyn, which is much harder to bore through, the rock in Manhattan is soft and easy to excavate. "It cuts like butter,” Chestman said. Above: A view of the tunnel boring machine from 7 stories above. Photo: Jonathan Snyder/Wired.com

There are no fossils or archeological relics or precious metals. No pockets of oil or huge amounts of groundwater. The drill just effortlessly bores a hole into the earth leaving a smooth, beautiful cylinder behind. It’s sort of ironic, after so much turbulence, the actual act of boring underneath Manhattan for this line is turning out to be the easiest part of the whole endeavor. That could change though. As the project continues, geologists will have to negotiate a latticework of preexisting tunnels, pipes and cables. There are also pockets of sand, silt and clay, all of which could make drilling tough. Above: The beginning of the 22-foot-diameter tunnel. The machine will churn through the rock with almost 3 million pounds of force. That’s about the same amount of power as 50 747 jet engines. Photo: Jonathan Snyder/Wired.com

For the next year, the giant drill will chew its way through the Manhattan schist until it reaches the 63rd Street line. Upon reaching that juncture, the machine will be reversed out of its tunnel and moved to drill another parallel tunnel all the way to 63rd Street again. Estimates for completion of the tunneling are around November 2011, although many critics point out that unforeseen issues in funding, stability of surrounding buildings, and personnel could delay the project by years. But eventually the line will be completed. The new line, called the T, will operate from 125th Street to Hanover Square. A grand opening is optimistically scheduled for 2016. Once it gets going, it will transport over 200,000 riders per day. The cost in both time and money is immense though. After over 75 years of false starts, billions of dollars, and untold numbers of hours worked, today’s New Yorkers will finally have the subway line generations have been clamoring for. Above: Jay Walder, Chairman and CEO of the MTA speaks with reporters. Photo: Jonathan Snyder/Wired.com