What comes first?: track or signalling?

[jimbo]

Plans for Cockfosters and Arnos Grove track layouts under DTUP state: preferred layout dependent upon contracted signalling system.

Can anyone explain this? I would have thought that you decide on the track layout you need, then signal for the moves required. I know it may have to wait a while for some money now!

[rincew1nd]

I suppose there is an outline track layout, which is then tweaked with input from signalling (eg if we move this bit the overlap for this signal won't be compromised and you can have a faster clearance of the junction).

[goldenarrow]

I'm not very familiar with the lay of the land at that end of the Picadilly. Could it be that there is some form of rationalisation of the track layout planned and the scale of such a rationalisation is dependant on the signalling product offered up?

[superteacher]

Nov 17, 2019 14:15:02 GMT goldenarrow said:

I'm not very familiar with the lay of the land at that end of the Picadilly. Could it be that there is some form of rationalisation of the track layout planned and the scale of such a rationalisation is dependant on the signalling product offered up?

I doubt that they can possibly rationalise any track at Cockfosters given that reducing flexibility there would have a detrimental effect on the line, considering the lack of reversing capacity elsewhere.

[Chris L]

Nov 17, 2019 17:52:12 GMT superteacher said:

Nov 17, 2019 14:15:02 GMT goldenarrow said:

I'm not very familiar with the lay of the land at that end of the Picadilly. Could it be that there is some form of rationalisation of the track layout planned and the scale of such a rationalisation is dependant on the signalling product offered up?

I doubt that they can possibly rationalise any track at Cockfosters given that reducing flexibility there would have a detrimental effect on the line, considering the lack of reversing capacity elsewhere.

There was a proposal some years ago to add an extra platform at Cockfosters.

[superteacher]

Nov 17, 2019 18:59:27 GMT Chris L said:

Nov 17, 2019 17:52:12 GMT superteacher said:

I doubt that they can possibly rationalise any track at Cockfosters given that reducing flexibility there would have a detrimental effect on the line, considering the lack of reversing capacity elsewhere.

There was a proposal some years ago to add an extra platform at Cockfosters.

Wasn’t it Oakwood?

[jimbo]

Nov 17, 2019 22:06:38 GMT superteacher said:

Nov 17, 2019 18:59:27 GMT Chris L said:

There was a proposal some years ago to add an extra platform at Cockfosters.

Wasn’t it Oakwood?

Enjoy my summary of PPP proposals at the time: Piccadilly: 92 new trains will replace the current trains in 2013. In addition a new signalling system, with a new line control centre at South Kensington, will be commissioned by 2014. There will be new signalling control centres at Acton Town and Arnos Grove, together with additional platforms at Cockfosters and Oakwood. These works result in a 20% improvement in journey times and a 20% increase in capacity.



These were the only track/station improvements listed for any line under PPP. Today the talk is of 60% uplift with no additional platforms. If Victoria line can operate 36tph shuttle between two platform termini, any more is a luxury!

[Chris L]

Nov 17, 2019 22:06:38 GMT superteacher said:

Nov 17, 2019 18:59:27 GMT Chris L said:

There was a proposal some years ago to add an extra platform at Cockfosters.

Wasn’t it Oakwood?

See jimbo's response.

My recollection was before PPP.

Given that only 2 of Stratford's platforms are used for most of the day nowadays it seems it is no longer needed.

[MoreToJack]

The more platforms you have, the more conflicting moves you have.

Stepping back works best with 2 platforms, and is generally considered the best way to increase capacity - as we see with the Victoria line, turn around times can be reduced to seconds (Victoria line averages around 100 seconds at Brixton).

[Ben]

Does this suggest that Stanmore's third platform was perhaps a bit of a white elephant?

[Chris M]

A third platform is very useful in times of disruption, and at times of the day where throughput is not the key determining factor and stepping back is not in use as it allows longer layovers which is better for service recovery. All three platforms at Stratford are used at the extremes of the day for example.

[t697]

Perhaps the final targets for Picc line are also relevant here. As others have mentioned, reversing 36tph off two platforms is fairly easy with Train Operator Stepping Back, but if you don't want to use Stepping Back you probably need 3 platforms. But if the final target is to eliminate Train Operators would you build another platform in the interim?
I am not up to date with end goals, or is that GOAs?

[100andthirty]

Reversing 36 trains in a tunnel happens because there is guaranteed adhesion, with over runs beyond the platforms and crossovers long enough to allow train to follow their high rate braking curve.

Absence of any one of these factors would compromise achieving the throughput. The only one of these factors that can reasonably easily be fixed at open termini is the crossover length and position. Hence 36 tph reversal in the open is challenging.

Edited to correct the errors introduced by my tablet's autocorrect.

[t697]

Yes, that probably gets us to the track or signals answers. I don't recall how much overrun space there is at Cockfosters but maybe with a good ATC you could reverse 24tph there and 12 at Arnos middle road. And if the ATC or more particularly the ATC/train integration isn't that good, then you might need an extra platform.
Need to be able to use the available wheel/rail adhesion to get good run-in and run-out times. So that will also affect whether new crossovers allowing faster speeds through them are part of the solution to get the performance wanted.