On Monday morning, a malfunctioning switch motor on the subway tracks beneath midtown Manhattan caused significant delays for commuters, coinciding with the debut of the new F & M train swap.

Described by one insider as an instance of “terrible luck,” the motor controlling a critical switch at the 5th Ave. – 53rd St. Station malfunctioned overnight. This unfortunate incident occurred just as the F and M lines were poised to commence their revised routes.

The updated service plan aims to streamline and accelerate subway traffic between Manhattan and Queens by exchanging the East River crossings for the F and M trains on weekdays from 6 a.m. to 9:30 p.m.

Under this new schedule, M trains now traverse the East River using the 63rd St. tunnel, making stops at 21st St.-Queensbridge, Roosevelt Island, Lexington Ave.-63rd St., and 57th St. They then merge with the F line at Rockefeller Center to continue along the Sixth Avenue route.

Conversely, F trains, which previously utilized the 63rd St. tunnel, are now rerouted through the 53rd St. tunnel. They share tracks with the E train and stop at Court Square and Queens Plaza in Queens, as well as Fifth Ave. and Lexington Ave. in Manhattan.

This rerouting strategy, which reverts during nights and weekends, is designed to prevent peak-hour trains from crossing paths at a complex network of switch tracks located under Long Island City, referred to as the 36th St. interlocking.

NYC Transit President Demetrius Crichlow said Monday that the swap will rid straphangers of a problem they’ve had “for years.”

“You’re waiting at Queens Plaza and you’re waiting for that E train, and all of a sudden that M local cuts in front of you and you’re waiting — that will be a thing of the past,” he told reporters at Roosevelt Island.

The dead switch at 53rd St. should serve to split the F from the E and send it downtown along the Sixth Avenue line. But Monday’s Manhattan meltdown meant F trains had to take the scenic route and follow the E down the borough’s west side, until it could rejoin the M at the West 4th St. Station.

Work crews were still in the process of repairing the switch Monday afternoon, with the MTA expressing hope the lines would return to (their new) normal in time for the evening rush.