Sometimes, in this world, a small thing beats\h a big thing. David beats Goliath, a pea beats a\h\h
princess, a few leaves delay hundreds of trains by\h thousands of hours a year. Yeah, as it turns out,\h\h
fallen leaves are a huge problem for choo choos,\h causing misparks, damage, delays, and at least\h\h
one really annoying sound. But how? I mean, can’t\h dad just clear the tracks once he’s done with the\h\h
lawn? Apparently, no. The problem’s way stickier\h than that, and all the solutions are weirdly\h\h
sci-fi—but I’m getting ahead of myself. How\h does this thing do such a number on this thing?\h
Well, here’s the thing about this thing: it\h only works if there’s the exact right amount of\h\h
friction between these things and these things.\h Obviously, if you want your train to zoom fast,\h\h
you want to minimize friction. Hard metal wheels\h help because, unlike air-filled tires, steel\h\h
wheels barely deform under the weight of what\h they’re carrying, meaning a tiny contact point,\h\h
less rolling resistance, and faster rolling. The\h coefficient of friction between train wheels and\h\h
tracks is around or under 0.5, versus about\h 0.9 between rubber car tires and a dry road.\h\h
But trains, rather famously, have to stop—so\h they need some friction between the wheels\h\h
and the tracks, to be more specific,\h a coefficient of friction over 0.17.\h
But when Mr. Leafy and his buddies come to\h town, the friction on the tracks can get as\h\h
low as 0.015, because leaves are, by accident of\h evolution or trick of God, perfectly engineered\h\h
to make train tracks extra super slippy. By the time a leaf falls off a tree,\h\h
it’s mostly made of water, cellulose, pectin, and\h fatty acid. And when you smush the full weight of\h\h
a train on that via contact points the size of\h an HAI writer’s thumb, you apply a gigapascal\h\h
of force—and no, I don’t know what a gigapascal\h is either, but I assume it’s one billion Pedro\h\h
Pascals punching as hard as they can… which\h would do unspeakable damage to a person,\h\h
and does something similar to leaves. Namely,\h turning them into a slimy black sludge that’s\h\h
conveniently bonded to the top of the rails.\h Which is a problem, because trains can’t always\h\h
brake fast enough on slippery rails, so they might\h mispark in a station and have to reverse back in,\h\h
or just skip it entirely if they can’t\h slow down in time to stop there… which,\h\h
along with messing up train schedules, induces\h an as-yet-unstudied-but-presuambly-lethal\h\h
amount of rage in people who miss their\h train while standing on the platform.\h
Along with the human psyche, leaf sludge damages\h wheels. Sometimes, a slip-slide will trigger a\h\h
train’s automatic emergency brake, which will\h cause the wheels to skid along the track and\h\h
wear parts of them down flat. And something\h cool about flat-bottomed steel wheels is that,\h\h
along with not working so good, they make a super\h loud clangy sound every time they hit the rail. So\h\h
oftentimes, they need to be replaced. All of this\h causes delays: from correcting misparks to taking\h\h
trains out of service for repairs. And beyond\h that, there’s also signal problems: the sludge\h\h
messes with signals, so trains pass them without\h signaling to trains behind them that they’ve\h\h
passed, so those trains get held up waiting for\h clearance that they should already have. In 2015,\h\h
leaf sludge caused 5,800 hours of delays on\h rail lines in the UK. So this is a big problem,\h\h
and the easy solutions don’t work. You can’t\h send dad in with a rake because the leaves are\h\h
sludge. You can’t pull up all the trees\h near tracks because A, in the UK alone,\h\h
that’s more than 13 million trees, and B, without\h trees’ root systems holding land together under a\h\h
lot of tracks, there would be landslides,\h which would probably cause more delays.\h
So how do you deal with this? Sometimes,\h trains get equipped to lay a traction gel\h\h
with sand particles in it on the tracks to\h give themselves some extra grip. Sometimes,\h\h
rail operators run special trains to pressure-wash\h the lines, spraying 48 gallons of water per minute\h\h
through a wee pinhole on the bottom of the train.\h The UK’s Network Rail ran 61 jet-cleaning trains\h\h
in 2021, and these were also the main system in\h place for cleaning commuter trains in the New\h\h
York Metro region for years, with two such\h trains cleaning the entirety of the Harlem\h\h
and New Haven lines every single day for six\h weeks in the fall. This method is effective,\h\h
but it’s inconvenient. And beyond that, it’s\h kinda boring. Believe me, I wouldn’t be making\h\h
this video if the coolest solution out there\h was “rinsing off the goo.” No, dear viewer.\h\h
The solutions here are cooler. Solutions like: Ultrasonic bubbles! Thermal ablation with megahot\h\h
plasma! Electromagnetic braking! Shooting tiny\h dry ice pellets at the track that flash-freeze\h\h
the sludge, then sublimate into a gas that blasts\h the frozen sludge off the track! All of those are\h\h
cool. But the coolest? That would be LASER TRAINS! Yeah, baby! That’s right! Laser trains! Last fall,\h\h
the MTA ran a pilot program where they strapped\h lasers to the bottom of a commuter train. Those\h\h
lasers fired infrared beams at the tracks wherever\h there was leaf sludge at just the right wavelength\h\h
to reflect off the tracks without damaging them…\h while still completely vaporizing the sludge. It\h\h
was a huge success: during the pilot program,\h there was a 40% reduction in emergency stops\h\h
from slip-slides, and wheel repair costs reached\h record lows. This fall, they’re adding a second\h\h
laser train to the team, meaning all vital parts\h of the Metro North system will be laser-cleaned\h\h
once a day, which is conveniently how long the\h rails stay clean before more sludge forms. So\h\h
that’s one point to laser trains, zero points to\h leaves. It just goes to show: sometimes the little\h\h
guy beats the big guy. But if you give the big\h guy lasers, he can almost always pull it back.\h
The world always has problems, some of which\h potentially even more pressing than slippery\h\h
train tracks, but many are getting progressively\h solved thanks to the ingenuity of those who have\h\h
dedicated their careers to doing good. It\h is actually, genuinely possible to have a\h\h
career that is both fulfilling and financially\h sustainable—it just takes a little more work to\h\h
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