The Metropolitan Transportation Authority (MTA) announced the official start of leaf-fighting season, with crews from the Long Island Rail Road, Metro-North Railroad and the Staten Island Railway operating work trains that spray water jets to clear tracks of slimy leaf debris.

A specialized Metro-North work train sprays water at high pressure, and specially equipped highway/rail trucks use rail scrubbers to remove crushed leaf residue from the tracks. On-board Metro-North diesel passenger trains, "sanders" automatically drop sand onto the tracks to help improve traction and reduce wheel slippage. On the LIRR, a specialized train then applies a traction gel onto the freshly cleared rails that allows train wheels to maintain traction, even in the presence of crushed leaf slime.

Video of the LIRR’s leaf-fighting train performing a demonstration:

During autumn when falling leaves land on the running rails of MTA tracks, they can be run over by trains, compacted by the weight and crushed into a gelatinous, slime-like substance that reduces the normal amount of adhesion train wheels have on the rails. This creates a condition known as “slip slide,” which prevents trains from stopping normally when engineers apply the brakes. To ensure safety, the railroads institute slower speeds for trains passing through an area where an engineer has reported slip-slide conditions, which can cause train delays.

“Anyone who has ever driven a car and tried to brake on a patch of ice knows something of what it feels like for a train engineer who applies the brakes to a train on a patch of rails coated in liquefied leaf residue,” said MTA Chairman Joseph Lhota. “As autumn begins we turn our attention to fighting leaves that have fallen on our tracks, but throughout the year we work to combat vegetation along the rails.”

The first step to reducing these delays for the LIRR, Metro-North and the Staten Island Railway is to trim or remove trees and vegetation alongside the tracks, either through railroad personnel or by hiring outside trained and licensed vegetation management contractors. About two thirds of the leaf matter that interferes with railroad operations on Long Island comes from invasive species such as ailianthus trees, black locust trees, Norway maples, and bamboo. In the region served by Metro-North, the majority of the leaves come from oak, sugar maple and birch trees, and sumac.

The Long Island Rail Road alone plans to engage contractors to trim back vegetation along 80 miles of track in 2018 and 94 miles in 2019. Bushes and trees on LIRR property are subject to removal, and tree branches extending onto railroad property may be pruned as well.

But despite those continuous annual efforts, of course it’s impossible to completely prevent leaves from falling onto the tracks. So each fall, the LIRR, Metro-North and Staten Island Railway use the specialized trains to spray jets of water to push leaves from the rails, and either scrub the tracks clean, as on Metro-North, or, as on Long Island, apply a mixture known as sandite, a traction gel that has the consistency of pancake batter and provides improved traction.

The MTA has programmed its newest commuter railroad cars — the M7’s and M8’s — to allow their braking systems to better adjust to slip-slide conditions, and train crews and dispatchers communicate continuously to identify slip-slide problem areas where trains need to slow, and where the specialized leaf-fighting trains may need to travel next.