New Yorkers have been waiting nearly a century for the new second avenue subway. But the line that begins service this weekend is far smaller than the one riders were promised decades ago. And it's unclear if the full line will ever be built. NY1's Jose Martinez takes a look in the final part of our series, "A First for Second Avenue".

With its gleaming new stations, open concourses and striking public art, the Second Avenue subway line that opens to the public Sunday will impress riders.

But it's less than a fifth of the line that was first proposed nearly a century ago. 

By that measure, the project is far from done.

"And if we don't do it, then New York's future is really in jeopardy. But it's nice to see the efforts that were put in for the last 15 years," said former MTA Executive Director and CEO Elliot Sander.

For decades, the transit system's planners envisioned the Second Avenue subway running 8.5 miles from 125th Street in Harlem to Hanover Square, in Lower Manhattan.

The line that opens New Year's Day will run just 1.5 miles from 96th to 63rd streets. Which is why some are calling it the Second Avenue "stubway".

"You have to have a champion, somebody who says 'This is the most important project,'" said former MTA Manager of Planning Phillip Mark Plotch.

The hurdle for the MTA, as usual, is money.

It took nine years and four and a half billion dollars to build the segment opening New Year's Day.

At that rate, realizing the dream of building the entire line will cost tens of billions of dollars.

"You don't take no. And if they say no, you figure out how to get them to say yes," said Congresswoman Carolyn Maloney.

The MTA hopes the project can be built in three more phases. 

The next stage, phase two, would extend the line from 96th to 125th Streets. A billion dollars has been set aside for initial planning work.

Phases three and and four would extend it south from 63rd Street. No money for that has been approved.

"It was much more difficult to get it started when it was a dream, when it was a mirage, when frankly, it was a joke. But I think now when people start using it and seeing it, yes, I think it will happen," Sander said.

If the Second Avenue Subway is extended south of 63rd Street the MTA says it will be called the T line. That's T as in time, because that would take a long, long time to happen.