A sudden braking caused a train derailment in Harlem, injuring 30 people and causing massive transit disruption. View Full Caption TWU Local 100

WEST HARLEM — Investigators are trying to figure out why an emergency brake suddenly activated and derailed a southbound A train near West 125th Street and injured more than 30 people Tuesday morning, officials said.

The southbound A train was pulling into the 125th Street stop when the brake suddenly snapped on and sent two of its eight cars off the rails and into the subway tunnel wall about 9:48 a.m., officials said.

“The emergency brakes automatically went on. The train bucked forward, it bucked backwards, and in the process of doing that, there are eight cars on this train, two of the cars derailed. They scraped the side of the walls,” MTA Chairman Joseph Lhota — who recently returned to the position after stepping down in 2012 — said at a press conference at the scene.

“The brakes went into emergency. We need to determine why they went into emergency ... until the train is removed, we really don’t know the full extent of what’s there. We’ll be able to know that over the next couple of hours,” Lhota added.

Investigators are still piecing together how fast the train was going and how the brakes triggered, but "numerous transit workers and investigators" were combing the tunnel to find out, Lhota said.

"We're evaluating right now what caused the brakes to go into emergency. We do not know. That investigation is ongoing," Lhota added.

Tony Utano, the Transit Workers Union Local 100 vice president for the Maintenance of Way, said that the damage caused by the accident was extensive.

"It's a serious derailment, with quite a bit of damage to signals and some structural damage to the walls," he said. "Our members are working as fast and safely as possible to bring the system back to normal."

Lhota — who helmed the MTA from October 2011 through December 31, 2012, including leading the agency through Hurricane Sandy — returned to his former post last week amid a crush of bad press and disastrous infrastructure conditions.

Lhota nodded to the crumbling conditions and underfunded repairs at Tuesday's press conference, but said that initial investigations don't seem to indicate any mechanical error. But he said it was too soon to say since the cause has not yet been determined.

He added that the fire and smoke conditions were caused by trash on the tracks ignited by sparks from the derailment.

"This does not look like a failure on the part of equipment," Lhota said.

He added that he intended to "restore confidence" in the beleaguered agency and that New Yorkers should be able to get to school and work safely and on time.

"One of the things that I’ll do while I'm here is to rebuild the confidence in the ability of the MTA. We transport millions of people every day. We want to do it safely. We want to do it as quickly and as efficiently as we possibly can, the way we've always done it and the way we will continue to do it," Lhota said.

Governor Andrew Cuomo, who controls the MTA board, has not issued a statement on the accident.

City Councilman Ydanis Rodriguez, chairman of the Transportation Committee, called for a line-by-line audit of the MTA budget.

"The system is in crisis. Emergency measures need to be taken," the councilman's spokesman Russell Murphy said.

Rodriguez endorsed closing down train lines for emergency repairs to ensure rider safety. He said that nearly $55 billion has been allocated to capital improvements over the last decade, some of which has yet to be spent.

"The system is failing. We want to make sure that the money is going to the right places, because that's a lot of money for a system that is not up to snuff," Murphy said.