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November 03, 2008

Leaves and Loco's

It sounds like a question on a kid’s quiz show: “How do you stop a train?”

A) Hail it like a cab? B) Pull the emergency brake? C) Put wet leaves on the track?

If you chose “C”, you were correct… and you must be a regular commuter on Metro-North.

This is the time of year that tries train engineers’ souls and commuters’ patience. One day last week, 60 rush-hour trains were delayed by “slippery rails” when wet leaves caused trains to “slip-slide” on their usually solid tracks.

You may not realize it, but the flanged wheel of a train only contacts the rail in a surface area the size of a dime. That’s why trains can move so smoothly with minimal power… riding a small, but firm area of friction.

But when the leaves fall and later get wet, they are ground into one of the slipperiest substances known to man, a compound called pectin. As the train rolls along, its computer senses the slip and tries to apply the disc brakes which eventually scrape off the goo.

But often the brakes are applied so hard that a locked wheel is ground against the track creating a flat-spot on the usually round surface. In years past these flat wheel issues have taken 25% of cars out of service for regrinding.

Sophisticated train computers don’t like it when they think the train can’t stop, so on the new M7 cars running in Westchester county the railroad had to reprogram the safety systems to reassure them the train wasn’t out of control and didn’t need emergency braking.

Worse yet, on some lines the slippery leaves can virtually leave the trains unable to move. Case in point, the Danbury branch line is almost a continual up-hill climb from Norwalk to “The Hat City”, 397 feet above sea level. On this branch, diesel locomotive-pulled trains can’t stop on hills at stations like Cannondale, so on some days they skip such stops and make a running start for the steeper climbs.

On an MU (multiple-unit) mainline train, all cars are locomotives, spreading out the traction-power the full length of the train. But on a branch line, a single Genesis locomotive weighing 120+ tons has only eight wheels touching the track, seeking enough traction to pull a fully loaded eight car train.

Sometimes the solution is as simple as sand dropped from special hoppers on the train just in front of the drive-wheels. The resulting friction gets the train going or helps it stop.

This is a problem for railroads worldwide, not just here in the northeast.
Of late, Metro-North has brought in heavier armament… a specially designed car dubbed “Water World” equipped with high pressure hoses that blast the tracks free of the gooey mess.

They’re also experimenting with chemical sprays. And one inventor in the UK is proposing to zap the goo off the rails with lasers!

So in the fall when we appreciate the gorgeous foliage, remember the words of Paul Simon: “Slip sliding away, slip sliding away. You know the nearer your destination, the more you’re slip sliding away.”

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