A leaf-fall question

Yup all Amersham and all 8 car Cheshams leave 3 mins earlier in leaf fall

well it is downhill and the spedos are not that good leaf fall speed limit is 40mph norm 50mph

Yes. A special timetable booklet is produced for passengers. Some years ago this would identify itself as the leaf-fall timetable, with some information about the problem and how LUL worked to resolve it. One year (at least) the cover was the northern end of the line shown vertically, with autumn leaves coming from it - rather inventive! For the last few years the timetable has had no mention of leaf-fall through.
I understand that during the season Chiltern are banned from running two-car units on their own, and that a switch is operated somewhere to change the signalling system. One of our signalling experts can probably give more details.

There is a sequential signalling switch that if a track "bobs" it will keep signals to the rear at danger - IMSO or Somer will be able to explain further!

Two car Chilterns are not allowed in the peaks.

As to the timetable, sadly anything inventive went out whe TfL came in...

I read where back in the day, uncoupling was not allowed during leaf-fall.

Indeed, but the Met. is the Metropolitan.

It's not the only part of the Underground with leaf-fall problems, but the reason that it gets a special timetable and signalling is that it's an uphill gradient all the way from Rickmansworth to Amersham (and then beyond, to Dutchlands summit). Adhesion problems are made worse by the gradient; downhill trains have to brake more gently to avoid skidding and getting wheel flats - hence the extra time allowed between stations.

Yes the Amersham branch is the only part of LU with a public timetable. The frequency is poor during the peak period so I can understand why a timetable is published!

Interestingly it is not only the Met that provides adhesion trains-Chiltern also have trains to do this. There is a green class 115 DMU (lovely to see and hear it in action too) which applies sand, and there is a bubble car (class 121/122?) that also operates.

Yep this is because of the leaves forming a mulch which can electrically separate the train from the track, thus causing the track circuit to "pick up" under a train. The danger of this being - in normal operation - the potential of a green signal behind a train.

So the sequential signalling is switched in - if the track circuits are not operated in the correct sequence i.e. one after the other in the normal direction of travel, this will set the signal concerned to danger and also one in the rear. It can be reset by a TO, but this is not allowed during traffic hours so the only other way to get round it is for a train to apply the rule through the area and (hopefully) operate all track circuits in the correct sequence thus allowing signals to clear behind it. Any clearer?

the chiltern train is actually a water jetter, you hear the jets hissing away as the train passes through and see the spray on the sleepers and rail after the train goes

If they kept the timings the same the trains would probably still arrive on time. I have the leaf fall season and everything that comes with it.

Oh well you live and learn, I explained it the way it was taught to me (which is obviously wrong!).

The green unit only sprays water. We do the sand laying with 710.

We're going round in circles here aren't we?

To clarify:

Network Rail (aka Chiltern) do water spaying
LUL (aka A stock Rail Adhesion Car) lay Sandite