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The Metropolitan Transportation Authority will shut the express subway tunnel between 36th and 59th street stations for a full year starting in spring of next year to repair rusted beams that are at risk of collapsing, according to members of Community Board 7.

Storm water has corroded the so-called “T beams” that support the tunnel, and workers must replace the buttresses between 40th and 58th streets, according to board members familiar with the plan.

The shutdown will be an inconvenience for straphangers, but the work is critical, because the tunnel is in such bad shape, according Community Board 7 transportation committee chairman Zachary Jasie, who met with transit officials on Jan. 10 and gave a report during the board’s Jan. 18 general meeting.

“This is work that needs to be done — that’s the bottom line. There’s profound deterioration of the center support structure of the tunnel for these 18 blocks. There is no choice in the matter, because it’s going to cave in on itself,” said Jasie.

A spokesman for the authority denied that the agency is telling community board members that the tunnel is in such bad shape.

“Unbelievable. Where do you guys get this stuff, or do you just make it up along the way?” said agency spokesman Kevin Ortiz. “The tunnel is NOT on the verge of ‘caving in’ as you so eloquently state, and there is no danger to our customers.”

Over the years, street-resurfacing projects on Fourth Avenue have raised the roadbed in such a way that rain water now runs into subway grates instead of sewer drains — and that errant flow has rusted underground beams, said Jasie.

As part of the tunnel work — which is set to run from May 2018 to May 2019 — transit workers will also install new drains and raise the sidewalk vents to prevent water from spilling into the subway, according to community board members.

Work will take place eight blocks at a time in four-month intervals and will require the city to close a lane of Bay Ridge-bound traffic, said Jasie. The Department of Transportation has agreed to place traffic agents along the construction to help drivers navigate the roads, he said. N trains will run on the local line during the year-long project, according to Jasie.

Locals are concerned that the lengthy construction will place strain on the R line and result in sluggish service, but one community leader emphasized the need for the decaying line’s repairs.

“This is 100-year-old infrastructure we’re dealing with,” said Daniel Murphy, chairman of Community Board 7. “This is sorely needed.”