Discussion of signalling headways

[jayah]

Mod Note: Split from https://www.railforums.co.uk/threads/the-decline-of-gwr.163329/

In terms of IETs, a very significant cost of running unnecessarily long trains is the additional fuel. Given that diesel operation of some sort or other is going to be with us on GWR for a very long time, this cannot be ignored.

In terms of numbers of peak paths, there seems to be a misconception that the signalling headway is the critical factor. It is not - the critical factor is the number of platforms at Paddington and the throughput capacity of the station throat. The ML planning headway is now 2 mins, previously it was 3 mins, was recently reduced in agreement with Network Rail. The technical headway is as low as 80 seconds in places, at 125mph linespeed. So in theory you could run 30tph (although in practice this would be performance suicide) but in reality the absolute maximum is 18tph, and this can only be sustained temporarily in the evening peak, and requires an absolutely rigid and well-planned platforming sequence, and uses 10 full-length platforms (HEX should be going down to 1-platform operation in the peaks.) The critical point is under Gantry 3 at Royal Oak, where many down departures cross Up arrivals (minimum margin 2-3 mins), defining a minimum platform reoccupation value of 5 mins at Paddington itself. When you add in the minimum turnaround times - generally 20-30 mins depending on inbound route - the real challenge presents itself. Crossrail has certainly not helped matters by removing Line 6, and NR are seriously considering a new pair of crossovers at Portobello Jcn to improve the number of ‘parallel moves’ to give the planners a bit more flexibility and the terminus a bit more robustness.

It is crazy for Network Rail to reduce the headway without actually increasing capacity. The 0-5 performance in the peaks is already less than 50% on many long distance services.

80 seconds sounds like nonsense. Can you find even a pair of trains running at line speed that get close? If two trains perfectly timed merged at a junction on green signals it might work once, but even pulling away from Reading it takes more than 80 seconds to clear the first section so it won't happen.

5min reoccupation is also crazy, the trains are often that late leaving because of 'congestion' already. How many trains would be backed up outside the station on your 80sec headway if one were 5min late leaving?

Have Hex actually agreed to one platform working in the peak?

 

[Wilts Wanderer]

It is crazy for Network Rail to reduce the headway without actually increasing capacity. The 0-5 performance in the peaks is already less than 50% on many long distance services.

80 seconds sounds like nonsense. Can you find even a pair of trains running at line speed that get close? If two trains perfectly timed merged at a junction on green signals it might work once, but even pulling away from Reading it takes more than 80 seconds to clear the first section so it won't happen.

5min reoccupation is also crazy, the trains are often that late leaving because of 'congestion' already. How many trains would be backed up outside the station on your 80sec headway if one were 5min late leaving?

Have Hex actually agreed to one platform working in the peak?

You quite clearly don’t understand what you’re talking about. How do you know it isn’t possible for successive trains at 125mph to be less than 2 mins apart? Have you ever stood there and timed them passing you?

The technical headway is the time it takes for a signal to return to green after the passage of a train at linespeed. I can assure you that 85 seconds is quite doable. It doesn’t apply at Reading, as the trains are not running at linespeed, they are stopping, so you have to add the dwell time, plus a performance buffer. This is why down ML services ideally alternate between P8 and P9, equally Up trains alternate between P10 and P11. It didn’t work with one platform each way at Reading, so you could only run 12tph.

 

[Wilts Wanderer]

5min reoccupation is also crazy, the trains are often that late leaving because of 'congestion' already. How many trains would be backed up outside the station on your 80sec headway if one were 5min late leaving?

Have Hex actually agreed to one platform working in the peak?

How do you define ‘crazy’? Can you actually quantify that allegation, or is it just opinion. If a platform is occupied beyond booked time, the signallers start to replatform. It is very rare for every platform to be occupied at the same time, there’s normally something going out, or about to. Yes, trains start to back up, but at 18tph there are ‘gaps’ that gradually absorb the delay and the service recovers. It would be nice for every terminus to have 50 platforms, but unfortunately Paddington only has 13 and it does very well to support the service it currently operates, within acceptable performance limits. Life would be a lot better if the bloody NR signalling didn’t fall over every few hours somewhere on the GWML.

I believe HEX have agreed it in principle but the exact details are still under discussion.

 

[jayah]

How do you define ‘crazy’? Can you actually quantify that allegation, or is it just opinion. If a platform is occupied beyond booked time, the signallers start to replatform. It is very rare for every platform to be occupied at the same time, there’s normally something going out, or about to. Yes, trains start to back up, but at 18tph there are ‘gaps’ that gradually absorb the delay and the service recovers. It would be nice for every terminus to have 50 platforms, but unfortunately Paddington only has 13 and it does very well to support the service it currently operates, within acceptable performance limits. Life would be a lot better if the bloody NR signalling didn’t fall over every few hours somewhere on the GWML.

I believe HEX have agreed it in principle but the exact details are still under discussion.

You have said that the plan relies on a rigid platforming sequence, which will last until the first train from Worcester, Swansea, Hereford or Plymouth is running 6 mins late and has to swap paths with something behind it. Everybody who uses Reading - London knows it doesn't work today and cutting the planning headways to stuff more trains through the same infrastructure will only make it worse. The railway will not run on time until the people running it learn to plan for the infrastructure that exists not the infrastructure they wish existed.

If you need quantities, find me a train that achieves a 90sec headway and maintains linespeed which of course is necessary to reach London on time? Have a look at recent train times, see the 0-5 figures on the peak services for yourself. Today 14 trains leaving Paddington 0730-0900 were >5 late away, yesterday it was 6 with another cancelled, on Monday it was 11 with one cancelled.

 

[The Planner]

You still sound confused, we don't plan trains as 90 second headways but Wilts Wanderer is bang on, there are loads of locations where the green to green time is less than 90 seconds. I know of locations on the WCML where its as low as 70-75 but we plan at 3 minutes for robustness. Techincal and planning headways are different beasts.

 

[jayah]

You quite clearly don’t understand what you’re talking about. How do you know it isn’t possible for successive trains at 125mph to be less than 2 mins apart? Have you ever stood there and timed them passing you?

The technical headway is the time it takes for a signal to return to green after the passage of a train at linespeed. I can assure you that 85 seconds is quite doable. It doesn’t apply at Reading, as the trains are not running at linespeed, they are stopping, so you have to add the dwell time, plus a performance buffer. This is why down ML services ideally alternate between P8 and P9, equally Up trains alternate between P10 and P11. It didn’t work with one platform each way at Reading, so you could only run 12tph.

I have just told you why it is only possible if two perfectly syncronised trains merge at a converging junction at full speed and there ample data available on places like realtimetrains if you want to try and prove otherwise. I don't need to stand on a platform with a stopwatch, there is an App for that.

Today for example 1K31 left Reading plat 11 at 1925.5 and 1P42 platform 12 at 19.26.75. By Maidenhead despite the following train being faster, they were 1937.5 and 1939.75 respectively and that is a close as they get in that part of the world. Nobody is going to pull away from Reading towards a red at full throttle and by the time the first signal clears the first train must be two sections clear of the platform.

This doesn't even look doable to me, but remember it must happen train after train for 2 hours in each peak.

 

[Wilts Wanderer]

(Very) simple mathematics proves technical headways are extremely short at 125mph.

Four aspect signals are sited 1-mile apart on average. This provides 2 miles stoppage from double-yellow to red, and HSTs were designed to stop in 1.5 miles or better from linespeed, for which the signal spacing was optimised in the 1970s. Current signalheads have been replaced with LED searchlights but the positioning is generally the same.

At 120mph (slightly below linespeed), a train covers 2 miles every 60 seconds. Therefore three signal sections are covered in 90 seconds. This is therefore the green-green time, I.e. the technical headway. You can see that at 125mph, 85 seconds is possible. Especially that some of the signal spacings are tighter than 1-mile apart, close to London (I think the Ealing/Hanwell area are very tight.)

The real headway needs to account for sighting time (min 7 seconds) and also allow for the fact that a driver will not apply full power if the signals are only clearing to green immediately in front of him. Anything above that is simply a performance buffer. The size of that buffer is effectively agreed by consensus.

Where the planning headway becomes awkward is where either trains do not run at linespeed, or lines converge. If I was a timetable planner, I would ensure that trains departing Paddington 2 mins apart would do so along different lines (e.g. First train via Line 1, Second train via Line 2) and only converge onto the same line at Ladbroke Grove travelling at linespeed. Then the platform clearance time at Paddington is no longer a risk to the second train starting on time. Barring any adverse signals, and assuming two trains of identical performance that can run at 125mph, there is absolutely nothing to prevent them both running on clear signals all the way to Reading. As the linespeed reduces approaching Reading, the signal spacing starts reducing by a proportional amount, therefore the second train should continue receiving clear aspects all the way into the platform, assuming alternate platforms are used for successive services.

 

[Wilts Wanderer]

I have just told you why it is only possible if two perfectly syncronised trains merge at a converging junction at full speed and there ample data available on places like realtimetrains if you want to try and prove otherwise. I don't need to stand on a platform with a stopwatch, there is an App for that.

Today for example 1K31 left Reading plat 11 at 1925.5 and 1P42 platform 12 at 19.26.75. By Maidenhead despite the following train being faster, they were 1937.5 and 1939.75 respectively and that is a close as they get in that part of the world. Nobody is going to pull away from Reading towards a red at full throttle and by the time the first signal clears the first train must be two sections clear of the platform.

This doesn't even look doable to me, but remember it must happen train after train for 2 hours in each peak.

There is a severe flaw in your data. 1K31 is a Bedwyn-Paddington service formed with a 90mph Turbo unit. Therefore it cannot run at 125mph linespeed, and therefore the technical headway is not achievable or applicable. Equally, if they are timed that closely together (and I’m assuming 1P42 is an HST or 800?) the second train will have pathing time allowances in the schedule, to account for receiving signal checks.

There is another aspect to consider - timetables are planned at 1/2 min accuracy, therefore there is a measure of rounding in the sectional timings. This can easily produce a variance of +/- 15secs on any given section without actually being an error - the variances cancel each other out over a longer stretch of running.

 

[jayah]

You still sound confused, we don't plan trains as 90 second headways but Wilts Wanderer is bang on, there are loads of locations where the green to green time is less than 90 seconds. I know of locations on the WCML where its as low as 70-75 but we plan at 3 minutes for robustness. Techincal and planning headways are different beasts.

So why do they plan 3min for 'robustness' on the WCML and 2min on the GWML? I can see plenty of trains on both routes holding at 3min apart and slightly less, but not 90sec.

 

[jayah]

(Very) simple mathematics proves technical headways are extremely short at 125mph.

Four aspect signals are sited 1-mile apart on average. This provides 2 miles stoppage from double-yellow to red, and HSTs were designed to stop in 1.5 miles or better from linespeed, for which the signal spacing was optimised in the 1970s. Current signalheads have been replaced with LED searchlights but the positioning is generally the same.

At 120mph (slightly below linespeed), a train covers 2 miles every 60 seconds. Therefore three signal sections are covered in 90 seconds. This is therefore the green-green time, I.e. the technical headway. You can see that at 125mph, 85 seconds is possible. Especially that some of the signal spacings are tighter than 1-mile apart, close to London (I think the Ealing/Hanwell area are very tight.)

The real headway needs to account for sighting time (min 7 seconds) and also allow for the fact that a driver will not apply full power if the signals are only clearing to green immediately in front of him. Anything above that is simply a performance buffer. The size of that buffer is effectively agreed by consensus.

Where the planning headway becomes awkward is where either trains do not run at linespeed, or lines converge. If I was a timetable planner, I would ensure that trains departing Paddington 2 mins apart would do so along different lines (e.g. First train via Line 1, Second train via Line 2) and only converge onto the same line at Ladbroke Grove travelling at linespeed. Then the platform clearance time at Paddington is no longer a risk to the second train starting on time. Barring any adverse signals, and assuming two trains of identical performance that can run at 125mph, there is absolutely nothing to prevent them both running on clear signals all the way to Reading. As the linespeed reduces approaching Reading, the signal spacing starts reducing by a proportional amount, therefore the second train should continue receiving clear aspects all the way into the platform, assuming alternate platforms are used for successive services.

I can do maths. A few things you haven't considered is the train is 260m long, and the back of it must clear an overlap at 125mph that might be conservatively 250m beyond the protecting signal. In this day and age trains are driven cautiously not like racing cars at full speed until half way between a double yellow and yellow aspect. A double yellow aspect will be seen hundreds of metres ahead of the post and a positive response will be made. In reality to be driven to green signals, the front of each train is separated by around 3miles + 500m ahead of the protecting signal and 500m behind the green signal as follows:

Front of Train
250m
Rear of Train
250m
protecting signal (R)
1m
signal (Y)
1m
signal (DY)
1m
signal (G)
500m sighting
Front of following train

At 120mph this gives you around a 1.8minute headway. Of course as soon as the leading train encounters a fleeting signal check, the train following will overbrake on cautionary aspects in the absence of any dynamic traffic regulation and fall further behind.

 

[jayah]

There is a severe flaw in your data. 1K31 is a Bedwyn-Paddington service formed with a 90mph Turbo unit. Therefore it cannot run at 125mph linespeed, and therefore the technical headway is not achievable or applicable. Equally, if they are timed that closely together (and I’m assuming 1P42 is an HST or 800?) the second train will have pathing time allowances in the schedule, to account for receiving signal checks.

There is another aspect to consider - timetables are planned at 1/2 min accuracy, therefore there is a measure of rounding in the sectional timings. This can easily produce a variance of +/- 15secs on any given section without actually being an error - the variances cancel each other out over a longer stretch of running.

I have chosen the two services all day that left Reading as close together as possible. As the following train is faster, you would expect at some point they would at least touch the technical headway, but they don't and the faster train falls further behind than when they set off. I am still waiting for some evidence of a real train holding a 90sec headway at 125mph!

I am not looking at whats planned here, only what happened.

 

[The Planner]

So why do they plan 3min for 'robustness' on the WCML and 2min on the GWML? I can see plenty of trains on both routes holding at 3min apart and slightly less, but not 90sec.

They can't hold at 90 seconds apart as you need the combination of the leading train slowing down and speeding back up before the following one sighted a restrictive aspect, however if you planned them 90 seconds apart then there is a good chance they would stay like that if no other issues occured. As for the difference between the GWML and WCML it is purely what has been agreed as robust. If the WCML required it then it would be considered.

 

[Wilts Wanderer]

The WCML is an interesting comparison, as it is a reasonably segregated Fast / Slow Line operation at the southern end (ie south of Watford) and has very uniform 125mph rolling stock but only has a 3-min planning headway. This surprises me, especially as Euston has a grade separated throat to limit the number of in/out conflicts and a 3-min platform reoccupation value at the terminus. With a technical headway as low as 70sec, a planning headway of 2 mins (non-successive) would not be unreasonable.

 

[Wilts Wanderer]

I have chosen the two services all day that left Reading as close together as possible. As the following train is faster, you would expect at some point they would at least touch the technical headway, but they don't and the faster train falls further behind than when they set off. I am still waiting for some evidence of a real train holding a 90sec headway at 125mph!

I am not looking at whats planned here, only what happened.

The viability of planning headways for trains under linespeed is a very valid point and one that timetable planning does not tackle very well, on a national basis. You need two trains at 125mph to demonstrate the minimum technical headway, running at a consistent speed and unperturbed by adverse signals. As soon as you’ve got a fast following a slow train the exercise becomes meaningless.

 

[jayah]

The WCML is an interesting comparison, as it is a reasonably segregated Fast / Slow Line operation at the southern end (ie south of Watford) and has very uniform 125mph rolling stock but only has a 3-min planning headway. This surprises me, especially as Euston has a grade separated throat to limit the number of in/out conflicts and a 3-min platform reoccupation value at the terminus. With a technical headway as low as 70sec, a planning headway of 2 mins (non-successive) would not be unreasonable.

70sec isn't possible as I have explained it is nearer 2min. Planning for something that is barely possible in theory let alone reality is not at all sensible.

Where have you read there is a 3min reoccupation for Euston? I can only see 3min for a platform end conflict. Is 3min ever planned?

 

[The Ham]

We have gone a long way from rare, to not universal. I have given lots of examples.

With 2x5 there aren't more lease costs as you have got the 10 vehicles already. There are probably lower costs as there are fewer cabs and certainly fewer crew vs coupled in service, and which it sounds like a lot will be.

I wouldn't agree that running a longer train off peak 'gets you less money' and given the sums spent on capacity increases it doesn't seem right to be building 15% short on capacity.

Getting that 15% more capacity through infrastructure will be vastly more expensive, the only rational argument is that the capacity definitely won't be needed for the foreseeable future and I would propose that is certainly not true in this case.

You gave an example of the SWML with lots of 10 coach trains in the off peak, I pointed out that that on long distance services (i.e. not the metro) there were a few services off peak an hour that are 10 coach trains.

As such, just on that basis 10 coach trains are not universal, although on that line in the off peak they are far from common.

I've also pointed out that where you pointed out a TOC which does run a lot of 11 coach units (Virgin) that these had a lower number of seats than the 9 coach trains which you wanted to run as 10 coach units. As such just because a train is long it doesn't mean that it has a lot of capacity. Also there's a significant number of 9 coach 390's.

Beyond Virgin and SWR what other examples have you given? As I've missed them.

I know that when it was LM they had 4 coach services which ran all day, again making it not universal.

I don't know enough about lots of the TOC's that run services out of London, but to be common then a lot of the services would need to be 10 coaches long.

However, to be a fair comparison to GWR's you would need to show that the longer distance services were the ones that were running as 10 coach services in the off peak.

This would need to include Brighton, Ashford, Cambridge, Colchester, Banbury, Milton Keynes, Woking, and the like.

To Woking they are not common and are fairly rare (at most 6 out of 20 if you include the Woking Stoppers, otherwise it's upto 4 out of 18). To MK on Virgin they are fairly common but not universal as 40% of the 390's are 9 coach units. However, what about the other MK services?

To Banbury none of the loco hauled sets are 10 coaches (even if you count the DVT and Loco) I don't know about the 16x's but I would be surprised if many of them, if any, are 10 coaches.

To Ashford several of the services are run by the 395's which are 6 coaches long, now some services could be run as pairs (but again I don't know numbers) however I would be surprised if a lot of them were 12 coach trains in the off peaks.

Based on the above and other services that I've used in the off peak on some of the other TOC's in/out of London, most of which (which if IIRC) were 8 coaches or less, I would question if 10 coach services made up even 1/3 of the medium/long distance services out of London (which serve as a fast/semi fast services those places listed above). If it does I wouldn't be surprised if it didn't reach 50% of services, however I would be surprised if it got above 60% (bearing in mind that of the two TOC's I recall you giving as an example only one reached 60% and the other was a LONG way short of that.

In fact probably the best TOC that uses 10 coach trains in the off peaks, other than Virgin, is likely to be GWR.

 

[The Planner]

70sec isn't possible as I have explained it is nearer 2min. Planning for something that is barely possible in theory let alone reality is not at all sensible.

Where have you read there is a 3min reoccupation for Euston? I can only see 3min for a platform end conflict. Is 3min ever planned?

Why isn't 70-75 seconds as a technical headway possible? As has been discussed, the sighting time plus the distance from the green to the red, plus the overlap and the length of the preceding train can get down to 70 ish seconds in several locations. There is no reason why trains couldn't be that far apart if the situation arises in a particular location, professional/defensive driving standards of each TOC (they all vary) means they will sit back though as you have correctly mentioned in that they can "read through". However, we cannot assume the read through as we have no idea of the sight lines. It is a recognised industry process to assume the driver is "blind" until that measured sighting distance. You will also struggle to find examples of running at less than headway as trains will only report at timing points in their schedules and these can be miles apart, it doesn't mean they cannot close up and spread back out inbetween.

The 3 minute reoccupation for Euston is there in the Timetable Planning Rules which I assume you have been checking. Euston has no defined value in section 5.3 so it defaults to the standard "opposite direction" value, which is in the standard values section at departure vs conflicting arrival of 3 minutes. Just because its in the rules, you don't have to use it, they are minimum values.

 

[jayah]

Why isn't 70-75 seconds as a technical headway possible? As has been discussed, the sighting time plus the distance from the green to the red, plus the overlap and the length of the preceding train can get down to 70 ish seconds in several locations. There is no reason why trains couldn't be that far apart if the situation arises in a particular location, professional/defensive driving standards of each TOC (they all vary) means they will sit back though as you have correctly mentioned in that they can "read through". However, we cannot assume the read through as we have no idea of the sight lines. It is a recognised industry process to assume the driver is "blind" until that measured sighting distance. You will also struggle to find examples of running at less than headway as trains will only report at timing points in their schedules and these can be miles apart, it doesn't mean they cannot close up and spread back out inbetween.

The 3 minute reoccupation for Euston is there in the Timetable Planning Rules which I assume you have been checking. Euston has no defined value in section 5.3 so it defaults to the standard "opposite direction" value, which is in the standard values section at departure vs conflicting arrival of 3 minutes. Just because its in the rules, you don't have to use it, they are minimum values.

Well if you can find an example of a successful 3min reoccupation being achieved, good luck. As I have explained at length, which you don't want to address, 90sec at 120mph is 3 miles or 3 signals. The signal would change double yellow to green around 500m after the leading cab passed under it, assuming the signals change instantaneously. Therefore it will not be driven at linespeed.

Again as per Wilts Wanderer you are free to use the vast amount of open source running data to show otherwise.

 

[jayah]

You gave an example of the SWML with lots of 10 coach trains in the off peak, I pointed out that that on long distance services (i.e. not the metro) there were a few services off peak an hour that are 10 coach trains.

As such, just on that basis 10 coach trains are not universal, although on that line in the off peak they are far from common.

I've also pointed out that where you pointed out a TOC which does run a lot of 11 coach units (Virgin) that these had a lower number of seats than the 9 coach trains which you wanted to run as 10 coach units. As such just because a train is long it doesn't mean that it has a lot of capacity. Also there's a significant number of 9 coach 390's.

Beyond Virgin and SWR what other examples have you given? As I've missed them.

I know that when it was LM they had 4 coach services which ran all day, again making it not universal.

I don't know enough about lots of the TOC's that run services out of London, but to be common then a lot of the services would need to be 10 coaches long.

However, to be a fair comparison to GWR's you would need to show that the longer distance services were the ones that were running as 10 coach services in the off peak.

This would need to include Brighton, Ashford, Cambridge, Colchester, Banbury, Milton Keynes, Woking, and the like.

To Woking they are not common and are fairly rare (at most 6 out of 20 if you include the Woking Stoppers, otherwise it's upto 4 out of 18). To MK on Virgin they are fairly common but not universal as 40% of the 390's are 9 coach units. However, what about the other MK services?

To Banbury none of the loco hauled sets are 10 coaches (even if you count the DVT and Loco) I don't know about the 16x's but I would be surprised if many of them, if any, are 10 coaches.

To Ashford several of the services are run by the 395's which are 6 coaches long, now some services could be run as pairs (but again I don't know numbers) however I would be surprised if a lot of them were 12 coach trains in the off peaks.

Based on the above and other services that I've used in the off peak on some of the other TOC's in/out of London, most of which (which if IIRC) were 8 coaches or less, I would question if 10 coach services made up even 1/3 of the medium/long distance services out of London (which serve as a fast/semi fast services those places listed above). If it does I wouldn't be surprised if it didn't reach 50% of services, however I would be surprised if it got above 60% (bearing in mind that of the two TOC's I recall you giving as an example only one reached 60% and the other was a LONG way short of that.

In fact probably the best TOC that uses 10 coach trains in the off peaks, other than Virgin, is likely to be GWR.

The arguments against running long off peak train such as leasing costs, track access charges, fuel/power are exactly the same however many seats they choose to put in each carriage.

 

[jayah]

The viability of planning headways for trains under linespeed is a very valid point and one that timetable planning does not tackle very well, on a national basis. You need two trains at 125mph to demonstrate the minimum technical headway, running at a consistent speed and unperturbed by adverse signals. As soon as you’ve got a fast following a slow train the exercise becomes meaningless.

All that is being demonstrated is that a 2min headway is not sustainable for successive trains and should not be used as a planning headway. There is ample data available showing this.

 

[jayah]

They can't hold at 90 seconds apart as you need the combination of the leading train slowing down and speeding back up before the following one sighted a restrictive aspect, however if you planned them 90 seconds apart then there is a good chance they would stay like that if no other issues occured. As for the difference between the GWML and WCML it is purely what has been agreed as robust. If the WCML required it then it would be considered.

There is 7 days of past data on RealtimeTrains for both WCML and GWML.

If there is a good chance of achieving and holding a 90sec separation at full line speed, what chance is there of either of you finding it and publishing it?

 

[The Planner]

Well if you can find an example of a successful 3min reoccupation being achieved, good luck. As I have explained at length, which you don't want to address, 90sec at 120mph is 3 miles or 3 signals. The signal would change double yellow to green around 500m after the leading cab passed under it, assuming the signals change instantaneously. Therefore it will not be driven at linespeed.

Again as per Wilts Wanderer you are free to use the vast amount of open source running data to show otherwise.

You are using Wilts Wanderers assumption that the signals are a mile apart, are they? Signal spacing is very rarely a fixed distance. If the signals are a mile apart or 1610m then if you assume 7 seconds sighting distance at 120mph (53.6m/s) you get 375.2m, 1609m x 3 for the signal spacing, 200m for a normal overlap and 260m for a train to clear. That comes to 5662m if I can add up correctly. Divide that by 53.6m/s to get your technical headway and it comes out at 106 seconds. I would agree that 14 seconds bunce is very risky for a 2 minute planning headway but the industry has agreed that it is acceptable. If the signal spacing is less than a mile that 14 seconds starts to increase.

 

[The Planner]

There is 7 days of past data on RealtimeTrains for both WCML and GWML.

If there is a good chance of achieving and holding a 90sec separation at full line speed, what chance is there of either of you finding it and publishing it?

Like I said earlier, probably nil as you only report at timing points unless you are anal enough to trawl through every single train that is perturbed as the timetable is based upon the planning values. Using a section of the WCML as an example between Hanslope and Hilmorton you only time at Weedon inbetween. That is a a distance of 25 odd miles where you only know the separation in 3 locations.

 

[jayah]

Like I said earlier, probably nil as you only report at timing points unless you are anal enough to trawl through every single train that is perturbed as the timetable is based upon the planning values. Using a section of the WCML as an example between Hanslope and Hilmorton you only time at Weedon inbetween. That is a a distance of 25 odd miles where you only know the separation in 3 locations.

No train actually runs to the timetable therefore you are indeed looking at what happened. RealtimeTrains uses berth data to report times every 1-3mins along the whole route. While the exact location of berths relative to stations isn't precise it will be a constant error and ideal for calculating separation. So if you are going to keep saying trains run at 125mph 75-90sec apart there is plenty of data for you to go and prove it.

 

[jayah]

You are using Wilts Wanderers assumption that the signals are a mile apart, are they? Signal spacing is very rarely a fixed distance. If the signals are a mile apart or 1610m then if you assume 7 seconds sighting distance at 120mph (53.6m/s) you get 375.2m, 1609m x 3 for the signal spacing, 200m for a normal overlap and 260m for a train to clear. That comes to 5662m if I can add up correctly. Divide that by 53.6m/s to get your technical headway and it comes out at 106 seconds. I would agree that 14 seconds bunce is very risky for a 2 minute planning headway but the industry has agreed that it is acceptable. If the signal spacing is less than a mile that 14 seconds starts to increase.

Why do you assume 7 sec? The minimum standard is 8 sec and on straight track they are visible much further.

I calculated 1.8min which is almost the same as 106sec and a lot more than the 75/80/90 sec some people seem adamant on. On that basis, 2min is total absurd for a planning headway on a real life railway. Was this by any chance agreed by the same company that promised to electrify to Swansea for half the money it is costing to get to Cardiff? It is rather familiar to see the railway digging a hole and climbing in.

What headway is used on the ECML? What does the GWML think is so special about their 4 aspect signals?

 

[The Planner]

No train actually runs to the timetable therefore you are indeed looking at what happened. RealtimeTrains uses berth data to report times every 1-3mins along the whole route. While the exact location of berths relative to stations isn't precise it will be a constant error and ideal for calculating separation. So if you are going to keep saying trains run at 125mph 75-90sec apart there is plenty of data for you to go and prove it.

Where did I say they do run that far apart, I said they could but you seem to be out for point scoring and the last word so I'll leave it here for you to gloat over.

Why do you assume 7 sec? The minimum standard is 8 sec and on straight track they are visible much further.

Ok, a whole second more which brings it to 107 seconds and you have glossed over the fact that I previously said we know that drivers can read through but we cannot accommodate that.

I calculated 1.8min which is almost the same as 106sec and a lot more than the 75/80/90 sec some people seem adamant on. On that basis, 2min is total absurd for a planning headway on a real life railway. Was this by any chance agreed by the same company that promised to electrify to Swansea for half the money it is costing to get to Cardiff? It is rather familiar to see the railway digging a hole and climbing in.

Again, you ignore the bit where I also agreed it was risky and its calculated on the assumptions the signals are a mile apart and it drops if the signal spacing is lower. It was agreed by both NR and all the operators as per the established processes for every item in the TPR.

What headway is used on the ECML? What does the GWML think is so special about their 4 aspect signals?

In the main 3, but 2½ on a section between Ally Pally and Woolmer Green. Download the Timetable Planning Rules, it sounds like you would have a field day picking fault with them as Im leaving this here.

 

[jayah]

Where did I say they do run that far apart, I said they could but you seem to be out for point scoring and the last word so I'll leave it here for you to gloat over.



Ok, a whole second more which brings it to 107 seconds and you have glossed over the fact that I previously said we know that drivers can read through but we cannot accommodate that.



Again, you ignore the bit where I also agreed it was risky and its calculated on the assumptions the signals are a mile apart and it drops if the signal spacing is lower. It was agreed by both NR and all the operators as per the established processes for every item in the TPR.



In the main 3, but 2½ on a section between Ally Pally and Woolmer Green. Download the Timetable Planning Rules, it sounds like you would have a field day picking fault with them as Im leaving this here.

Drivers are told absolutely not to read through signals.

So one 125mph main line has 3min, one has 2min another a bit of both. That isn't nit picking it is a railway that doesn't know even the basics of how to plan a timetable. That is probably not unconnected with the fact there are so many forum topics about timetables that don't work and trains that don't run on time.

Agreeing to shrink your headway from 3min to 2min without making any improvement to the infrastructure really is dire stuff.

 

[Wilts Wanderer]

Drivers are told absolutely not to read through signals.

So one 125mph main line has 3min, one has 2min another a bit of both. That isn't nit picking it is a railway that doesn't know even the basics of how to plan a timetable. That is probably not unconnected with the fact there are so many forum topics about timetables that don't work and trains that don't run on time.

Agreeing to shrink your headway from 3min to 2min without making any improvement to the infrastructure really is dire stuff.

You’re assuming that all 125mph railways have standard signal spacing which is patently not the case. Equally the traffic needs of each main line vary. The agreed headway may also reflect the mix of speed profiles of different types of traffic, allowing for slower traffic to be followed by faster without causing performance risks. There are quite a few instances of 4-min headways on two-track 125mph routes, this is effectively a larger ‘buffer’ between technical and planning headway for this very purpose. Whereas the fast or main lines of a 4-track route out of London tend to be dedicated to faster, more uniform rolling stock, so the margin can be less. Yes, min headway vs performance is a trade off, but it is a balancing choice.

To bring slightly back in topic, the GWR service was severely impacted this morning by a class 66 failing on the DM at Uffington and dumping most of its oil along a 1-mile stretch of railway.

 

[jayah]

You’re assuming that all 125mph railways have standard signal spacing which is patently not the case. Equally the traffic needs of each main line vary. The agreed headway may also reflect the mix of speed profiles of different types of traffic, allowing for slower traffic to be followed by faster without causing performance risks. There are quite a few instances of 4-min headways on two-track 125mph routes, this is effectively a larger ‘buffer’ between technical and planning headway for this very purpose. Whereas the fast or main lines of a 4-track route out of London tend to be dedicated to faster, more uniform rolling stock, so the margin can be less. Yes, min headway vs performance is a trade off, but it is a balancing choice.

To bring slightly back in topic, the GWR service was severely impacted this morning by a class 66 failing on the DM at Uffington and dumping most of its oil along a 1-mile stretch of railway.

The achievable headway is determined by the greatest signal spacing not the shortest. For some reason you are focussed on the latter which isn't relevant.

It is clear in comparing the planning rules both with theory, real life running and comparable routes that 2min on this route is a triumph of optimism over good sense. There is no balance when you have a 14 sec margin of error before trains are cautioned and delayed.

 

[SamYeager]

Drivers are told absolutely not to read through signals.

So one 125mph main line has 3min, one has 2min another a bit of both. That isn't nit picking it is a railway that doesn't know even the basics of how to plan a timetable. That is probably not unconnected with the fact there are so many forum topics about timetables that don't work and trains that don't run on time.

If only GTR, Northern & Network Rail had got you to write their latest timetables! Frankly this thread seems to have degenerated into jayah writing posts demonstrating that only jayah has access to the one true vision of how the network should be run interspersed with posts from the unknowing! All praise to jayah!