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Piccadilly Line stopping at Turnham Green.
- Thread starter Mawkie
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I assume this is because of the engineering works for the District line
MatthewRead
On Moderation
Surprised they're doing this now on previous weekend closures they don't stop at all due to them supposedly having to run at reduced line speed between Hammersmith and Acton Town which leads to stacking.
Thank you very much
MatthewRead
On Moderation
I hope London Underground do the same thing on the weekends of 4/5th & 25/26th October as there will also be no District line running but there is the Piccadilly line.
Dstock7080
Established Member
Certainly will for 4-5 October.
starlight73
Member
Is this because the signals are further apart at Turnham Green (Piccadilly line) to allow for larger overlaps?
Correct, 73 stock could run fast and slow in both directions between Acton Town and Hammersmith, but they removed the points at Hammersmith, so that can't happen now.
I think more to do with the time it takes to slowdown, serve the station, and accelerate again.
The train frequencies are reduced slightly over the weekend due to the additional stops at Turnham Green which will presumably help avoid this happening. It's not the normal timetable with Turnham Green stops added - the whole timetable has been revised.
MatthewRead
On Moderation
But on previous weekend closures like the 2 last year on 12/13th and 2/3rd November they didn't make any additional stops and I was told by London Underground it was to do with the frequency levels!
Which is why, as I said, the frequency levels have been slightly reduced so that this time they can stop at Turnham Green without (hopefully) causing any delays to the scheduled timetable. Obviously the powers that be have made the decision, perhaps based on feedback received for the closures last year. I don't know who decided what - just what is happening this time.
notverydeep
Member
- Joined
- 9 Feb 2014
- Messages
- 1,069
The problem with Piccadilly line trains calling at Turnham Green relates to the 'reoccupation time'. This is the combination of the time taken to run in from the 'home' signal, station stop (dwell) time and run out to the point at which the home signal can clear for the following train, this determines the minimum achievable headway at any point on a railway line. If must be less than the scheduled headway, as if it is not, the scheduled train throughput will not be achieved and trains will be held up and each subsequent train will be delayed to an increasing degree.
At Turnham Green normal early morning / late evening stopping only occurs when the headway is at least 165 seconds and this at times with lower traffic and hence a lower dwell time. At busier times, with a longer dwell time a 180 second headway would be required. This is above the peak scheduled headway of 150 seconds or 24 trains per hour (tph). At off peak times headways are a mix of 150 seconds and 165 seconds (rounding is to the nearest 15 seconds on this part of the Piccadilly line). This is why, the timetabled frequency must be slightly reduced if all trains are to serve Turnham Green - on Saturdays the reduction if from the scheduled 24 tph to around 20 tph. This will lead to more passengers having to stand for and do so for longer periods. Stopping also takes longer, so the 'round trip' time (that is the time between departing the origin station the first time, completing a return trip across the line, to departing the origin time a second time). Thus more trains are required to sustain the same frequency.
Because of the two above factors, routinely serving Turnham Green outside of its normal hours would require both signalling alterations and a larger fleet. While such a change would clearly improve things for Turnham Green passengers, it would be a loss for all the passengers that currently pass through Turnham Green non-stop as their journeys would be longer. This lengthening of run time by introducing extra stops is why the amount of extra traffic required to justify opening new stations across the UK rail network is surprisingly high...
[Edited to correct the current minimum scheduled headway at Turnham Green which should be 165 seconds - but I had typed 155 seconds - apologies]
At Turnham Green normal early morning / late evening stopping only occurs when the headway is at least 165 seconds and this at times with lower traffic and hence a lower dwell time. At busier times, with a longer dwell time a 180 second headway would be required. This is above the peak scheduled headway of 150 seconds or 24 trains per hour (tph). At off peak times headways are a mix of 150 seconds and 165 seconds (rounding is to the nearest 15 seconds on this part of the Piccadilly line). This is why, the timetabled frequency must be slightly reduced if all trains are to serve Turnham Green - on Saturdays the reduction if from the scheduled 24 tph to around 20 tph. This will lead to more passengers having to stand for and do so for longer periods. Stopping also takes longer, so the 'round trip' time (that is the time between departing the origin station the first time, completing a return trip across the line, to departing the origin time a second time). Thus more trains are required to sustain the same frequency.
Because of the two above factors, routinely serving Turnham Green outside of its normal hours would require both signalling alterations and a larger fleet. While such a change would clearly improve things for Turnham Green passengers, it would be a loss for all the passengers that currently pass through Turnham Green non-stop as their journeys would be longer. This lengthening of run time by introducing extra stops is why the amount of extra traffic required to justify opening new stations across the UK rail network is surprisingly high...
[Edited to correct the current minimum scheduled headway at Turnham Green which should be 165 seconds - but I had typed 155 seconds - apologies]
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Excellent post!
I did hear at work it would 'cost' two extra trains and 6 extra drivers to serve TG on a normal timetable (if the signalling changes were made as per your post).
One wonders how this can be the case when the same Piccadilly trains, certainly westbound, seem frequently to be brought to a stand outside Acton Town, and not just momentarily - it can be a minute or two, and passengers to Heathrow can start to fidget about whether something has gone wrong which will impact getting their flight.
boiledbeans2
Member
Yeah, often the District line trains are quicker than the Picc between Hammersmith and Acton Town.
If I want nostalgia, I wait for the Picc. But if I'm in a hurry, I get whichever train arrives first.
starlight73
Member
There are closing-up signals outside Acton Town (not sure of the right term) so trains can get closer to the platform as the one in front leaves. The signalling is designed around all trains slowing to stop at Acton Town (?). Whereas I think Turnham Green doesn’t have this. Thanks Davy and Mawkie!
I’ve figured that between Acton Town & Hammersmith, the District line takes approximately 4 minutes longer than the Piccadilly. So if the next Piccadilly train is in 4 minutes it would be about a similar time to taking the District.
I’ve figured that between Acton Town & Hammersmith, the District line takes approximately 4 minutes longer than the Piccadilly. So if the next Piccadilly train is in 4 minutes it would be about a similar time to taking the District.
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DavyCrocket
Member
- Joined
- 27 Oct 2006
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- 645
Closing up = multi home
I'm not a signaller, or a scheduler, but you're right (and wrong I think). The home signals at Acton Town are designed to get trains fairly close to the platforms, but Turnham Green also has 2 home signals (A630a/b), however they are very far away from the platforms, and I guess they are situated that way because of the speeds trains are usually doing through that section (line speed is 45mph on the Pic).
Yes, that's annoying for drivers and passengers alike! Numerous reasons for this, but often down to relieving drivers taking too long to set up their train when taking over.
I suppose to answer your point, the schedulers compile a timetable they know is achievable with the resources available at the time, and any minor occasional delays are accommodated in recovery time at each end. It wouldn't be acceptable to compile a timetable they knew couldn't be run reliably.
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Dstock7080
Established Member
Piccadilly Line trains will also be serving Turnham Green in both directions until 11.30 on 31 May, as there will be no District Line service until at least 10.00.
There appear to be no additional closing up signals at the running in ends of Turnham Green on the fasts while the slows used by the District have this feature. So the signalling isn't designed for Piccadilly trains stopping there routinely. When a resignalling is eventually implemented for the Piccadilly, the modern CBTC equivalent of closing up (i.e either moving or very short fixed block) should be available more widely and affordably, so a regular Turnham Green stop could plausibly be introduced if desired with the current maximum service frequency, given sufficient resources in new fleet and crewing due to the journey time increase.