A date is now set for the big switch between the F and M lines, the MTA said Monday.

Starting Dec. 8, the F and M trains will swap the tunnels they run through under the East River.

F trains will make stops at Queens Plaza, Court Square-23rd Street, Lexington Avenue-53rd Street and 5th Avenue-53rd Street.

M trains will shift to 21st Street-Queensbridge, Roosevelt Island, Lexington Avenue-63rd Street and 57th Street.

Transit officials say the swap is about more than just new stops.

“The most important part there is also allows us to be a more reliable service. And if an incident does occur, allows the incident to stay isolated to one of the lines and not, infecting, for lack of a better word here, the other lines around the area, allowing us to recover from incidents faster and making

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