We are on our leaf fall timetable at present. For us that means we run the trains a few minutes early and will do so from early October until around December. Leaf fall is a bit of a problem on railways and every year we have to work around it in a variety of ways. Re-jigging the timetable is one and there are some practical things we can do in terms of maintenance of the rails and our land but the autumnal onslaught is something we struggle with every year. Basically it's because leaves are bastards.
Leaves. Green things on sticks. Big sticks and ones with root systems but that's what it boils down to. The problem is that they don't stay there. Come the autumn they get flung off and blow about a bit. A fair quantity find their way onto railway tracks and at that point it's a slippery slope to doom.
The thing we hate about leaves is the sap. As discarded leaves naturally rot down they release tree sap. This stuff is incredibly slick and sticky and when you are running a vehicle with metal wheels balanced on metal rails then that's bad news. Every time the motors are applied the wheels have a tendency to spin uselessly for a bit before they can gain traction. Aside from the cumulative effect of many tiny delays caused by trains struggling to get started this causes damage to the wheels. This is bad enough but the issue is compounded because wheels which are damaged or flatted in one or more areas can in turn cause damage to the track. So not only do we have trains struggling to move and gradually accumulating bigger and bigger delays but we have both trains and tracks needing more than usual maintenance.
As ever, when there is a problem starting there is also a problem stopping. With slippery track it is incredibly simple to gently apply the brakes and have every wheel instantly lock up. The train then has the potential to slide along until friction eventually stops it. Naturally this will result in flatting of the wheels and again, that sort of damage is best avoided.
There are some solutions. We don't have a perfect solution but we have a few things going on to give us a fighting chance in the annual battle with nature. The first thing we do is cut short turnaround times at termini. In plain english that means the train will leave a few minutes early. This allows the train to run slightly slower but to still arrive at major interchanges around the same time. By running more slowly it obviously takes less time to bring the train to a halt in stations so that drivers don't need to brake so harshly. Another thing we do is change driving style. Braking starts much further out from a station and is much more gradual. Depending on the distance between stations I could start applying tiny amounts of brake from as far out as halfway whereas normally I'd not even think about it until I was a trainslength or so outside.
This slow, measured approach is crucial to keeping things moving. It adds a little extra to each journey time but on balance it cuts down delays. By keeping speeds down and braking gently and early trains are less likely to overshoot or slide straight through stations. It also reduces the likelihood of a driver being horrified as they slide straight towards a red signal. If you read my previous entry on failed signals you'll remember that when a signal is passed at danger (whether authorised or unauthorised) there is a procedure in place to maintain safety. And that this procedure takes quite a bit of time to complete. So accidentally flying through reds because the wheels are locked up is going to cause a huge delay (not to mention that the system instantly loses a driver as they are removed for interviews and investigation and if there is no spare around that means putting the train away too).
If you read that entry you'll also remember that if we are in any way not sure what's going on we have to default to the safest method of working. In the case of Signallers if they suddenly get a whole bunch of signals turning red for no apparent reason they have to assume it's because a train entered that area - even if there are no other indications of a vehicle being there. I mention this because the little leafy demons are responsible for delays in another way. The buildup of sap and decaying leaves can disrupt the signalling - essentially it short circuits the signals and these go to danger. The Signaller is then obliged to run the system with a failed signal and that takes lots of time to process.
One thing we try to do is to keep trees cut back on our land. Ideally they'll be no closer than a metre from the rails so that falling leaves will not go on the track. We have crews out for much of the year cutting back back large sections of foliage but it's a sisyphean task. With large amounts of LUL track being outdoors it's very difficult to strike a balance between maintaining wildlife habitat and keeping a working railway. And even though we cut back harshly, trees will have sprung up again within a few months. Even if we completely stripped our land of trees we'd still have leaves blowing in from other areas. So unless LUL can get a bylaw passed to institute treemageddon within the M25 boundary then we need to think up another means of dealing with leaf fall.
And we have one. Two, actually. One is to pressure wash the track. This is a tactic used by many companies which run on Network Rail track but with us being powered from the rails it's obviously not ideal to run a train through dumping water everywhere. So instead we lay something called Sandite. This is a mixture of sand which provides better traction and an enzyme which helps disperse leaf sap. Sandite comes from hoppers on a small train which pours it directly onto the running rails. It is not a perfect solution and needs replacing at least once per day but it makes a big difference in how easy it is to get trains running properly.
Various train operating companies also have systems on trains which are designed to stop the wheels spinning uselessly and locking up. It rather depends on the age of the train and who designed it as to whether this works well or not. Some are ok, some are a bit pants. But every little thing that is done to counteract leaf fall can give us a tiny advantage.
I think this is a war we are never going to win. Most of the time we are victorious in the yearly battles with hopefully only a few casualties in terms of sliding trains. But leaves are never going to leave and it's going to be at least another month before the Horror of Autumn is over. Just in time for the Horror of Winter with iced up power rails, frozen points and (you guessed it) sliding trains. It never rains but it pours.*
*If it rains we get slippery track and.... ;-)