The decision that will affect hundreds of thousands of commuters has been made: The L train will shut down between Brooklyn and Manhattan for 18 months in 2019, a spokesman for the Metropolitan Transportation Authority said Monday.

The MTA estimates 225,000 take the train under the East River each day. 

While service will be suspended from Eighth Avenue in Manhattan to Bedford Avenue in Brooklyn, the subway line will continue to run between Bedford Avenue and Rockaway Parkway.

The move comes as the MTA grapples with fixing flood damage from Superstorm Sandy inside the 100-year-old Canarsie Tunnel.

Earlier this year, the MTA announced it would have to close the tunnel — either entirely or partially — for an extended period of time in order to fix the salt water damage.

The agency had prosed two options: Shut down the tunnel entirely between Brooklyn and Manhattan for 18 months; or partially shut down the tunnel, allowing for some L train service, for three years.

The MTA said on Monday that it chose the 18-month plan based on an operational review and community input.

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“While the MTA always looks to avoid service disruptions, there is no question that repairs to the Canarsie Tunnel are critical and cannot be avoided or delayed,” MTA Chairman and CEO Thomas F. Prendergast said in a statement.

Prendergast vowed that the MTA would continue to work with commuters and transit advocates ahead of the shutdown.

“We are committed to working with the community just as closely as we develop ways to add service to help minimize the impacts of the closure,” he said in the statement.

The agency faced outrage from residents and transit advocates following its initial announcement of the planned shutdown after many felt it did not offer enough information, causing fear and confusion.

Masha Burina, community organizer at Riders Alliance, applauded the MTA’s decision on Monday.

“The MTA made the right call for 300,000 daily L train riders. But even the best option is painful for people who depend on the L train,” Burina said. “The MTA and the city have to put together an aggressive, comprehensive plan to serve L train riders from all of the communities that will be hit by this closure.”

The MTA said it is now beginning to develop plans for alternative service while the L train is shut down.