Stepping back on the Picc

IIRC Arnos Grove don't know if they still do.

There has been stepping back at other places: Hammersmith during the reconstruction in the 30s (only one platform face was in use - and yet they still managed to run a 2½ - 3 minute service). AFAICR stepping back at Arnos started up again in Jan 2008 (WTT43).

It still stands that the service density on the Picc is a little too much for Cockfosters to reverse the entire service.

I absolutely hate step backs. It just means an extra train on the duty. Get with it TfL, get another platform at Cfs, ASAP.......Please!

It's just weary. When I'm on a train I just want to crack on. It just irks me. Just a personal thing I suppose. Some drivers probably like it. I detest it.

If, in the body of my text, you're able to draw an inference to any type of 'enjoyment' my friend, you're very much mistaken.

Something like that...

Current timetable shows stepping back at Arnos Grove from 8.00 to 10.30, also 16.00 to 19.30.

It may be a coincidence, but there were just enough spare levers on the old Enfield West frame to put in another platform. Where would it have gone, to the left of the WB platform - ie leaving the depot connections alone?

Mixture of both the track arrangement and signalling. I was doing some research last night into the three platform termini on the Jubilee (Stanmore and Stratford) and looking at how the 'short-trips' were affected at Stanmore post-ATO.

I realise that a direct comparison with Cockfosters isn't ideal because of the differing track arrangements: Cockfosters has a central platform and both Stratford and Stanmore have an offset third platform.

However, post-ATO the cycle of platform re-occupation has been such that Stratford's platforms are used in the order 13, 14, 15 and Stanmore's are in the order 1, 3, 2. The idealised hope is that ATO would enable quicker platform reoccupation times and this is indeed the case, but you still have to allow for either changing ends or stepping back. ISTR that the minimum allowance for changing ends is set at something like 5 mins (this may have reduced slightly post-ATO, but I doubt it), then there is a standard 'gap' to be factored in with platform reoccupation times - again ISTR that there must be a clear ½ minute between an arrival and subsequent departure or the next arrival is 1½ minutes after a departure. Note that these guidelines are pre-ATO (but looking at the revised Victoria WTT with the new spangly ATO the times still hold) and apply to the entire terminus, not individual platforms.

OK, still with me? Now, remember the cycle of platforms that are worked through - this is stuck to fairly rigidly, although I have seen a Jubilee working where the cycle at Stanmore drops from 3 to 2 platforms. In this case there aren't any Wembley Park reversers (in Picc terms this would be that there aren't any Arnos Grove reversers), however during one of the transitions in the service there is a short period when only two platforms are in use at Stanmore, bu there is a series of reversers at WmPk, this continues as the service goes back up to three platforms in use at Stanmore - in this case it isn't quite so much that there isn't enough room at Stanmore, but evening out headways through the central area.

Now, during peak times, if you extrapolate out the Wembley Park - Stanmore transit time (average, rather than any weighting for different platforms) and also the North Greenwich - Stratford transit time you still end up with something like every third train reversing short at Wembley Park - simply because it would 'hit' the departing train on the station crossover: there are certain transitions where you can have three consecutive trains in a run to/from Stanmore and Willesden Green is used. In Picc terms that would be a Wood Green reverser. Likewise at the other end, there can be a pattern where every fifth train turns back at North Greenwich. Naturally, the 'missed' platform at either Stanmore or Stratford is cyclical.

So where would that leave us with the Picc at Cockfosters. Well, at the moment it tends to be every fourth train stops at Arnos Grove - I suspect on a very hasty bit of mental calculation that there will be the following scenarios

• no change in stock levels, status quo remains.
  • short transitional periods where there may be four consecutive trains to Cockfosters.
  • ..or.. using Arnos Grove for shorter periods without stepping back
  
  
• four more trains in service - less stand time round the T4 loop and a bit of trimmage at T5, Arnos arrangements would probably require stepping back.
  
• six more trains in service, stepping back at Cockfosters, every fifth train turns back at Arnos. Very little stand time at T$ and T5.

Now bear in mind, that this is just idle musing and I've got nothing more than gut feeling to base this on - I suspect that some of these idea may be quite wide of the mark, but I think that there will still be some Arnos Grove reversers post-ATO. It is of course possible to compile a beautifully elegant timetable, but within about 20 seconds of something sitting down in the ballast there is very little margin for service recovery.

Does that make sense?

Apart from the date and whose idea it was that's what I said V frame A/B in addition 15 was the yard lever(shaft).
I thought the V frames were the brain child of Dell.

Thanks for the explanation mrfs42 :-)

It still seems surprising that a 3 platform terminus of any track layout can't handle a higher density than those currently expected.

J P Thomas suggested back in the 1920's that somewhere with the track layout of old Hounslow West should manage about 40tph, and somewhere like Elephant could realisticly be expected to provide 30tph.

Surely if, almost a century on, it is beyond the capability of science, technology and research to design a signalling system that can provide the *same* frequency of service on the same track layout with the modern day increased requirement for 'safety' (or should that be requirement for reduced liability?) then somethings gone fairly wrong in the past 80/90-odd years... :/ :/