Defunct, non-existent subway trains keep getting spotted in NYC

This subway mystery has gone off the rails.

MTA trains have been baffling riders by running with line numbers that have been defunct for decades – or never even used in the first place.

Photos on social media show people on trains advertised as being defunct 9 and 13 lines or — even more mysteriously — 10, 11 and 12 ones, which have never been NYC subway lines.

And while the MTA confirms that the mystery trains’ manual “roll signs” have been altered, it has no idea who is to blame — whether it’s a series of accidents by MTA workers, or pranksters having fun, with some even posting how-to videos online.

“Those are regular trains with test signage that may have been temporarily displayed incorrectly,” an MTA rep confirmed to The Post, saying that crews are supposed to check signs before the start of every trip.

The roll signs for 9, 10, 11, 12 and 13 “lines” pictured on social media likely “just got scrolled too far past the current designation,” a spokesperson from the New York Transit Museum said, though experts are “not sure” if the recent sightings are due to crew errors or were knowingly altered.

Tampering with MTA signs could result in fines starting at $50. But would-be jokesters risk fines knowing a Big Apple audience will get a hoot out of the stunt.

“Gasp worthy,” one X user dubbed a sighting of a 9 train in Manhattan in a now-viral June post.

Others suggest that it is nothing new, with one commentator writing on a video showing how to change the roll sign: “I remember I used to do that as a kid.”

Experts say there’s a simple reason why unused routes like the 10 through 13 lines are included as possible line numbers in the first place.

It’s because “when roll signs were still being manufactured, they often included service designations (“bullets”) that could allow for route expansion,” New York Transit Museum curator Jodi Shapiro explained.

“For example, roll signs for trains that ran on routes of the former IRT (trains that are numbered such as 1, 2, 3) had a green 8 or 10, as well as a purple 11 and a red 13.”

That’s not to be confused with the BMT lines, which once ran elevated lines also numbered 10 to 16, according to Quartz.

“Some of [the numbers] were previously used on BMT routes,” Shapiro acknowledged. “However, it looks like the roll signs … in those photos were all taken on trains running on today’s IRT lines” such as the 1, 2, 3, 4, 5, 6 and 7 lines.

“For that reason, we would speculate that they were printed in case the authority wanted to use them for skip-stop service like the 9 was.”

Other roll signs on lettered trains include unused “P” and “X” service designations, likely in case the MTA ever wished to expand service, Shapiro added.

For some New Yorkers, witnessing the red express 9 Broadway-Seventh Avenue line is nothing short of a trip down nostalgia lane, as the 9 train was in service from 1989 to 2005 from Van Cortlandt Park-242nd Street to South Ferry.

Before that, it was used as a shuttle train in the Bronx from the 1940s and 1960s.

“Seeing that roll sign felt like stepping into a time warp,” one Redditor wrote of the 9 train.

Other straphangers, however, hope the flipped signs stay in the past: “It irritates me every time cuz I grew up on the 9,” another Redditor said, dubbing the express line “stupid and a waste of time.

“I’m glad it’s long gone.”