Mayor Michael Bloomberg says the expansion of the No. 7 subway line is on schedule and on budget. On a tour of the half-finished tunnel, more than 100 feet underground, with MTA chief Jay Walder nearby, the mayor says workers have not run into unexpected problems.

Paul Jareck is a foreman and says he was thrilled to see the mayor. Jareck, who came to the city from Poland seven years ago, says he never imagined he'd be part of such a massive project.

"Not even for a second, I was never thinking that I would be part of the history of New York, never was thinking about that," he says.

When completed the tunnel will extend the 7 line from Times Square to 34th Street and 11th Avenue, near the Javits Convention Center.

Bloomberg says the extension of the 7 line will spur development in the area. The majority of the project's funding comes from the city, and it's slated to be completed in December 2013.

Click here to see a slideshow of the underground construction and the mayor's visit.