New York City is in the process of making that subway system even bigger. It's adding a new line as part of the city's first major subway expansion in 50 years. New York transportation officials say once it's done, the new line will help reduce overcrowding and delays. But that's doesn't happen quickly and that doesn't happen cheaply.
Ali Velshi looks at what's involved.

Backhoe excavators that can cost $700,000 apiece, manlifts that sell for up to half a million bucks, see that hydraulic drill jumbo? They can go for 800 grand a pop. These are the machines of modern-day civil engineering.
New York City has them working full speed ahead on its new Second Avenue subway line.

Subways are expensive. Just to give you a sense of perspective , way back when the first subway in Manhattan was 21 miles, and it cost $35 million. This one, about a mile and a half, for about $4.5 billion. That's more than a billion dollars a stop.

And that's just for phase one. We went digging 10 stories below Manhattan to find out what goes into the bottom line on a new subway line.

It's a bargain. a bargain, $800,000 a pop.

The most massive piece of equipment used is the tunnel boring machine. The last time New York built a subway it used the cut-and-cover method, digging from street level. Boring is much more efficient and it disrupts life above ground a lot less.

The one that did this is 22 foot in diameter ,a little over two stories tall. It can go on average about 50 foot a day.

One of these things costs $12 million and requires 20 people to operate it. At 50 feet a day, boring two mile-and -a-half tunnels takes a long time.

But this is a linear project.Right.

You must do the tunnels before you do this.

And highly specialized laborers are the ones doing that. Sandhogs or urban miners work alongside operating

engineers who drive and maintain the machinery.

On average, we pay a guy about $1,000 a day, and that's base salary plus benefits .

It's putting people to work in a tough economy. The Metropolitan Transit Authority expects phase one of the subway-- that's 31/2 stops and a tunnel and a fourth stop -- to create 130,000 jobs with an economic impact of almost $18 billion over the nine years of construction.

New Yorkers keep asking why this takes so long.

It is normal.It is what It is normal. It is what it takes.

All the while, Americans are footing the bill, no matter where they live.

Second Avenue, right now, $1.3 billion come from the federal government and the rest of $3.15 billion comes from New York.

And in 2016, when we swipe our card and ride their first train, it's going to feel real good.

All right. It's time to have a little fun. Several weeks ago, we asked you to send us iReports of any questions you had for me. We had a great response to this. The full interview is up and ready to watch at

cnnstudentnews.com. You'll find it in the "Spotlight" section. If you want to know who comes up with all the puns,go there. If you want to see a sample of what this is all about, watch here.