Hundreds came out New Year's Day to ride the train in New York City, cheering as it left the station. That may sound odd, but this wasn't just any subway or any old station, it was the stuff of urban legend: the Second Avenue subway line.

To understand the crowd, you have to go back to the 1920s when the idea for the subway line was first floated, but never left the station because the Depression hit.

The idea was revived again in the 1950s as a replacement for the elevated trains, but city planner Robert Moses decided to spend money building expressways instead.

In 1968, the city finally got federal funding to build a subway on Second Avenue. It was expected to cost $220 million. The TV show Mad Men even worked in a reference to the plan when Peggy Olson, one of the main characters, goes apartment hunting on the East Side that year on the show.

But it didn't happen because in 1975 the city was broke.

By the 1990s overcrowding on the sole East side line had become untenable so the idea for a Second Avenue subway line was revived, and in 2004, a plan was approved. The first phase would include three new stations that go from 72nd Street to 96th Street. The Metropolitan Transit Authority even gave a deadline: 2013. And a cost: $3.8 billion.

But the public was skeptical, as that deadline was pushed back to 2015 and costs crept up. The MTA finally settled on Dec. 31, 2016.

On New Year's Eve, at a newly renovated station on 72nd Street, Gov. Andrew Cuomo held an opening night party. There was a five-piece band, a newsstand was converted into a beer bar, and the cavernous station was filled with purple, pink and orange lights. The governor helped secure more than a billion dollars in federal funding for the project and the MTA, and appoints their board members. At the New Year's Eve party he told the more than 500 invited guests that the Second Avenue Subway is vindication of his vision.

"We needed to show people that government works and we can still do big things and great things and we can still get them done," Cuomo said.

The final cost for the three stations, and two miles of track was $4.5 billion. And on Sunday morning, it officially opened to the public.

"I am so excited. I've been waiting for this for years and I'm thrilled to be on the first train," said 50-year-old Lillian Redel.

Redel, who lives nearby, says the new line will shave nearly 20 minutes off her commute. And the new stations filled with colorful tile art, including 12 portraits by the artists Chuck Close, are snazzy.

"I love the high ceilings, it looks like there might be some soundproofing so I'm really pleased about that," she said.

And this announcement is sweet music to her ears: "This is a Brooklyn-bound Q train via the Second Avenue line."

Nine-year-old train enthusiast Jared Margulis was impressed with the clean elevators, but had one suggestion: "I think they got to work on the train, because the train did not say the right stop that the train is going to."

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