(Bloomberg) -- New York’s Metropolitan Transportation Authority plans to shut down a subway tunnel for 18 months on its L train that carries passengers under the East River between Manhattan and Brooklyn, disrupting schedules for as many as 300,000 commuters a day beginning in January 2019.

The decision, announced Monday, was forced by damage due to saltwater that flooded the system’s Canarsie Tube during Hurricane Sandy in 2012.

The tunnel links Manhattan’s First Avenue and East 14th Street with Bedford Avenue and North 7th Street in Brooklyn’s Williamsburg section. The 24-station line operates between Eighth Avenue in Manhattan’s Chelsea east through Brooklyn, terminating at Rockaway Parkway in Canarsie.

Extensive repairs

The L train is one of New York’s busiest subway lines. MTA first announced in January that the tunnel would require extensive repairs. Officials and engineers weighed whether to close it entirely to work on it full time, instead of a one-track, three-year closure. MTA officials said that in visits with local Community Boards along the line, residents preferred complete, shorter-duration closing.

“Approximately 80 percent of riders will have the same disruptions with either option,” said Veronique Hakim, president of New York Transit, which runs the subways for the MTA. “It became clear that the 18-month closure was the best construction option and offered the least amount of pain to customers for the shortest period of time.”

Hurricane Sandy saltwater damage

Saltwater damage from Sandy caused corrosion to the tunnel’s walls, tracks and signal cables, one of nine tunnels to be flooded during the storm. Repair costs have been estimated as high as $800 million. Design and construction plans must begin this year to take advantage of hundreds of millions of federal dollars in financing for the project, the agency said in a news release.

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NYC&rsquo;s busy L subway tunnel line will close for 18 months in 2019

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NYC’s busy L subway tunnel line will close for 18 months in 2019