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It was called the L train apocalypse: a 15-month shutdown of a major subway tunnel between Manhattan and Brooklyn that would allow for critical repairs, but would cause one of the biggest transportation disruptions in New York City’s history, affecting 250,000 daily riders.
On Thursday, though, Gov. Andrew M. Cuomo announced an unexpected reprieve, saying that engineers would use a new technology from Europe to fix the tunnel without having to close it entirely.
The original plan would have shut the whole tunnel, starting on April 27, to repair damage from Hurricane Sandy’s floodwaters. Mr. Cuomo’s new plan could take about the same amount of time, but would keep full train service during weekdays and close one of the tunnel’s two tubes on nights and weekends.
The news was a head-spinning turn of events for Brooklyn residents who had rearranged their lives in anticipation of a shutdown that would sever their lifeline to Manhattan. They moved apartments. Changed jobs. Plotted new commutes. Rethought their social lives.
Of course, the announcement was also celebrated by the many New Yorkers who rely on the line. Shawna Pattishaw, 49, who lives in Bushwick and works in Manhattan, said the change was a blessing.
“I love this,” she said while riding the subway with her grandson on Thursday.
But Mr. Cuomo’s announcement also raised a barrage of questions: Would the new technology work? Has it been effective elsewhere? Why did the governor wait until the last minute to do this? Transit advocates also wondered how much the construction would cost and raised questions over whether Mr. Cuomo had made the decision unilaterally without consulting the Metropolitan Transportation Authority’s board.
Mr. Cuomo appeared pleased to have stepped in to save the day. The decision, he said, would be a “phenomenal benefit to the people of New York City.’’
The authority’s acting chairman, Fernando Ferrer, said the agency welcomed the new plan and planned to adopt it. Mr. Ferrer said the work could take about 15 to 20 months.
But some New Yorkers who already fled Williamsburg and other neighborhoods along the L line were frustrated. Andrew Klawiter was annoyed that he moved from Bushwick to Crown Heights to avoid the L train upheaval, only to have the shutdown called off.
”I was speechless for, like, half an hour,” Mr. Klawiter said of learning the news.
[The L train isn’t shutting down after all. What exactly does that mean?]
For months, subway officials have been preparing for the closing and planning alternate options for commuters, which would have included a significant expansion of bus service and more service on other subway lines. When the shutdown was announced in 2016, the news prompted panic in Brooklyn over what it meant for real estate and local businesses.
Mr. Cuomo had convened a panel of experts to consider other options for repairing the tunnel. He called the new design a “major breakthrough.”
“What these people have designed is the first of its kind in the United States of America,’’ said the governor, who was joined by the panel members. “No rail system has used this approach before. So it really is, from their point of view, exciting.”
“I don’t know if you can tell,” Mr. Cuomo joked, “but these engineers are excited.”
The new plan means that the L train’s weekday rush hour schedule would remain the same. Some trains would run at night and on weekends, but wait times would be longer.
The subway tunnel itself was structurally sound, the governor said, but the problem that needed to be addressed was salt water leaching into the tunnel and coming into contact with electrical components.
“Salt water and electronics do not mix,’’ Mr. Cuomo said.
A key provision of the alternative plan eliminates the need to replace major portions of the tunnel’s bench wall, which runs along the side of the tunnel and houses electrical cables. The cables were corroded because of damage from Sandy, Mr. Cuomo said.
Instead, using what engineers referred to as a “racking system,” new cables would be mounted on one wall and wrapped in protective material. A new power and control system would be installed, and the old cables housed in the bench wall would no longer be needed.
Last month, Mr. Cuomo, who controls the subway, toured the L train tunnel with engineering experts to see if there was another way to undertake the repair work.
“If there’s a better way of doing it, they tell us there’s a better way of doing it,” Mr. Cuomo said at the time. “If there’s not a better way of doing it, they say that’s the best that it can be done.”
Officials said the new plan also included improvements to make the tunnel more resilient in the event of a storm similar to Sandy. Those modifications included sealing openings that allow water to enter the tracks between the First Avenue station in Manhattan and the Bedford Avenue station in Brooklyn. The tunnel would also be equipped with technology to monitor its structural integrity.
The transit agency initially said the shutdown would be 18 months and later shortened it to 15 months. Subway officials had considered two proposals: a shorter, full closing of the tunnel or a partial three-year shutdown that would have allowed some trains to run.
They chose the full closure in an effort to do it quickly and limit the inconvenience for riders.