By way of explanation: in the spring of 1996 I was fortunate to cross paths with a gentleman bearing first-person knowledge of the "leaf issue" as it affects the British Rail system. What follows are his remarks to me regarding the problem.

Date: 12 Apr 96 15:21:19 EDT
From: "C.Hammond"
Subject: Leaf fall

Texas Heather,
Thanks for your note[...]. Re leaf fall and railways, this is a problem which causes problems throughout Europe. Bascically, in the autumn, leaves get pulverised on the track, causing an extremely slippery profile to the rails. Not only do light turbos find it difficult to stop, but they also 'disappear'. No, this is not something out of the X-Files - but in most of the world the exact position of train x on the tracks is known to a signaller by track circuits. What in effect happens, is that each rail is used to carry very low power circuit, which is caused to short circuit as the train passes along; these circuits are marked out in lights on track layout panels in signal boxes. Thus as a short circuit occurs the signaller can see exactly where it is located. However, when leaves get condensed on the track the trains can fail to make any electrical contact and thus literally disappear from the panel in the signal box. Obviously, the signaller has to stop all other trains on the line until he knows where it is located, thus causing delays.

But the real danger is trains being unable to stop.

Driving trains on leaf mulch is much like driving a car on black ice. The result can be worn outer rims of train wheels - which means a ride is bumpy until a lathe reprofiles the rim - and damaged motors costing thousand of pounds. Because these dangers are known, in the autumn drivers have to drive slower and allow greater time for braking, which leads to further delays.

The worst time is when light rain and broad leaves such as sycamore and chestnut fall on to lines. The leaves are crushed by train wheels and the pressure of successive trains, over 30 tonnes per square inch, carbonises the leaf content forming a hard Teflon-like coating. It is very difficult to remove.

There are a number of answers apart from slowing down trains. British Rail has fleets of Sandite trains, which spread a gritty paste on the rails. Some trains are fitted with anti-wheel slip devices and all wheel axles are motorised giving greater adhesion to the track. The real answer, however, is to cut down lineside trees and replace them with smaller leafed trees and shrubs - unfortunately this is not popular with environmentalists.

Anyway, I think that covers your point - bet you wish you hadn't asked now!

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