Outer-borough folks are learning what Metro-North riders have long known: Fallen leaves can severely foul up your commute.

The MTA has posted signs on subway lines that go outside, reports the New York Times, warning riders to expect leaf-fueled delays.

Subway riders who thought they had come across every reason for train delays — station fires, flooded tracks and sick passengers — have been presented with a new one: falling leaves.

Transit officials have put up about 500 signs along three subway lines in recent weeks warning that fallen foliage, “crushed by moving trains,” has been leaving a “slippery residue” that “may affect the train’s ability to start and stop.” Riders of the B and Q lines, which have several open-air stops in Brooklyn, and the Franklin Avenue shuttle in Brooklyn, which is completely exposed, were told to “allow for additional travel time.”

New Yorkers are not taking the news well.

“Because of leaves?” one rider, Sylis Gordon, asked incredulously on Wednesday as she waited for the Q train at the Parkside Avenue station. “That’s new.” She looked around her, noticing garbage on the tracks, but said, “There aren’t that many leaves.”

New York actor Chad Lindsey sounds like a cool cat. The guy jumped onto the subway tracks at Penn Station Monday to rescue a guy that had fallen and knocked himself out after a blow to the head.

Not only that, but the guy blended back into the anonymous city landscape after that. No Letterman, no cover of the NY Post, no tooting his own horn. Just an anonymous Joe risking his life to save a fellow human.

Pretty cool.

In fact, it was his friends who responded to a short article in the Times Monday about the incident.

An editor at The Times, Wendell Jamieson, said a crowd entered his car on the downtown C train, and the people were thanking and congratulating one among them, a disheveled fellow filthy with track grime.

The man, having already foregone any chance at glory by boarding the next train to pull into the station, declined to speak to Mr. Jamieson, unfortunately. We’ll never know what was going through this man’s mind during his dangerous time on the tracks.

Of course, Lindsey might flip the script, so to speak, and turn himself into the biggest media whore since Wesley Autrey. Since he’s an actor in a city that’s lousy with them, he probably should.

But for now, Chad Lindsey strikes us as a class act. Currently starring in an Off-Broadway show called Kasper Hauser, Lindsey told the Times the gravity of what he’d done didn’t really sink in until a few minutes later, after he’d boarded the C train that almost killed him and his benefactor, Theodore Larson.

“Then I sort of freaked out, and I was nervous and shaky. These five women opened their purses and gave me Handi-Wipes. I was covered in blood and dirt from the subway tracks.”

We’ve all seen someone fall on the subway. Unwitting dolts who didn’t anticipate the force of a train starting up from a dead stop.

Well, I joined their inauspicious ranks today. Perhaps still groggy from my week in the sun, I took a full-on tumble on a packed 6 train at rush hour.

Here’s how it happened.

The uptown 6 was nearly full at 28th. As we approached 33rd, I decided to move from where the doors were opening to a less-populated spot a few feet away. You know, make room for people. Do right by New York.

A large woman stood in my way. I said excuse me. She didn’t move. I muttered a sarcastic “thank you” as I squeezed between her and the pole, next to which a man and a woman shared a two-seater.

Mind you, the train had just pulled into 33rd. It wasn’t moving and I don’t think people had even started getting on yet. None of the usual fall-factors were at work.

I’d taken my backpack off back at 28th, again to free up room for my fellow riders (there’s more space for it swinging knee-level from my hand than clamped to my back), again to do right by New York. Perhaps that had me off-balance. Perhaps the dour, large woman threw a subtle hip-check.

Either way, I fell sideways, dropping 200 pounds of dopey Irishman onto the man and woman in the two-seater.

“I’m sorry!” I exclaimed as I jumped to my feet. People looked. People snickered. I cast a dirty look at the shrew, pretending it was all her fault. The train crawled out of 33rd, all eyes on yours truly.

We’ve all had someone fall on us on the subway. And unless we’re truly injured, we try to console them, assuage their humiliation. (If we’re injured, we smite them.) Not these two, especially the man, a prissy 40-ish Asian guy with a suit on. He pushed me away and hissed.

A week in Mexico, and I’ve lost my commuter skill. How long before it returns?