Photos: The Second Avenue Subway, Under Construction

The first leg of the the Second Avenue Subway is on track to open in less than one thousand days. It's the first major extension of the city's subway system in over 50 years.

Phase I will bring the Q train from 63rd to 96th Streets. It's currently two-thirds of the way done, and is estimated to cost $4.4 billion. Later stages will stretch north to 125th Street and down to Hanover Square in lower Manhattan, when it will officially be known as the T train.

While it will look similar to the subway system, there are some differences. In the summer, the stations will be about 10 degrees cooler than the outside temperature, due to the construction of giant ventilation shafts. (Pedestrians on the sidewalk above might notice the absence of subway grates.) And it will also be quieter. Low-vibration tracks will eliminate the screeching sound heard on other lines. And parts of the station walls will be lined with sound-absorbing materials. As Michael Horodniceanu, the president of MTA Capital Construction, put it: "when you are in the station you're not going to be able to yodel."

The first phase of the line will run from 96th Street to 63rd Street and is slated to open to passengers in December of 2016.

(all photos by Kate Hinds/WNYC)