The MTA says it will spend another $66 million to speed up construction work on the Second Avenue subway — an admission that its timetable for opening the long-delayed project was again in jeopardy, as NY1's Jose Martinez reports.

The city's biggest subway extension in decades has been taking shape below Second Avenue for years - and talked about for nearly a century.

But with the December deadline for its opening drawing ever closer, many residents along the route are skeptical they'll be riding the new Second Avenue subway anytime soon.

"Maybe not in my lifetime," said one straphanger.

"I've watched this being built," said another. "It goes to nowhere. The extensions won't be done for another 20 years. This is a boondoggle."

On Monday, there was more skepticism, as the MTA said it will spend another $66 million to accelerate the work in hopes of meeting the December deadline.

"The acceleration agreements will accelerate the completion of critical activities necessary to commence pre-revenue testing and training by September 1, 2016," said MTA spokesman David Cannon. "And revenue service in December 2016."

The plan is for contractors to work longer shifts, multiple shifts and on weekends to complete the project, which will bring subway service to 72nd, 86th and 96th Streets along second avenue.

Upper East Side residents aren't the only ones who remain skeptical about the project opening on time. On Monday, officials here at MTA headquarters in Lower Manhattan heard from their own independent engineering consultant, who said that the project remains a "moderate risk" of opening with a delay.

The Federal Transit Administration has also disputed the MTA's timeline — warning it's possible the line might not open until 2018.

Gene Russianoff of the Straphangers Campaign says such skepticism is well-deserved.

"The Transit Authority and the Second Avenue Subway are famous for false starts," Russianoff said. "They don't want also to be famous for a false finish."

But the General Contractors Association expressed faith in the new effort to fast track the work.

"Accelerating construction completion will give the MTA the time they need so that Phase I of the Second Avenue Subway opens by year end," the association said in a statement.

Riders should know soon enough how it's going. The MTA is promising monthly progress reports.