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