Thameslink Core and Network Rail

[GordonT]

There have been recurring and ongoing problems in recent days with signalling in the Thameslink core leading to speed restriction and consequential disruption including some cancellations of the usual suspects (Bedford-Gatwick Airport and Welwyn GC-Sevenoaks).

The tentacles from the core penetrate into what those of us of a certain age associate with the Eastern, London Midland and Southern Regions of prehistoric times.

Is there one coherent Line/Route/Region whatever of Network Rail responsible for infrastructure throughout the entire core?

If there is, they don't seem to do a particularly good job.

Or is it carved up between two geographical groupings for all infrastucture?

Or is (say) signalling a multiple carve-up which bears little resemblance to (say) the civil engineering carve-up (or non-carve-up)?

I'm just basically wondering whether the core is something of a cauldron into which multiple organisations and bits of organisations dabble with a lack of overall responsibility and accountability for performance?

 

[Bald Rick]

There have been recurring and ongoing problems in recent days with signalling in the Thameslink core leading to speed restriction and consequential disruption including some cancellations of the usual suspects (Bedford-Gatwick Airport and Welwyn GC-Sevenoaks). The tentacles from the core penetrate into what those of us of a certain age associate with the Eastern, London Midland and Southern Regions of prehistoric times. Is there one coherent Line/Route/Region whatever of Network Rail responsible for infrastructure throughout the entire core? If there is they don't seem to do a particularly good job. Or is it carved up between two geographical groupings for all infrastucture? Or is (say) signalling a multiple carve-up which bears little resemblance to (say) the civil engineering carve-up (or non-carve-up)? I'm just basically wondering whether the core is something of a cauldron into which multiple organisations and bits of organisations dabble with a lack of overall responsibility and accountability for performance?

it’s all managed and controlled by the NR Southern Region, from Three Bridges. Maintenance from London Bridge depot, albeit the OLE is covered by the team in Bedford (And always has been).

the current track circuit issue is causing much head scratching. Most likely to be related to the third rail power system.

 

[contrex]

I once saw a photo taken during preparations for Thameslink in the late 1980s, in Snow Hill tunnel, of an LMR/SR boundary post.

== Doublepost prevention - post automatically merged: 1 Jun 2022 ==

the current track circuit issue is causing much head scratching. Most likely to be related to the third rail power system.

(Southern fan here) Not those pesky wires up above?

 

[Nicholas Lewis]

Second day in row that Thameslink up the swanny through the core due to ongoing signalling issues.

 

[Fincra5]

Second day in row that Thameslink up the swanny through the core due to ongoing signalling issues.

Keeps getting fixed... well maybe "patched", then fails again. Been like it for a week or so it seems!

Was working normally until about 11am yesterday haha!

 

[swt_passenger]

I once saw a photo taken during preparations for Thameslink in the late 1980s, in Snow Hill tunnel, of an LMR/SR boundary post.

After the last major works in the Farringdon station area I thought that the territory boundary was moved just north of Farringdon’s platforms. That’s how the public online sectional appendix still shows it. But the signalling boundary extends much further, so presumably the signalling maintenance boundary goes with it. Or is that too logical?

Then what is the purpose of the territory boundary at (I think) the 66 chain distance from Moorgate?

 

[Supercoss]

Huge ammount of (rain) water fallen on entry to Smithfield sidings following roof work in connection with Museum of London building site which has taken over former Smithfield Market site, previous " dry" tunnel area now very damp directly around problem area causing PoSA signalling (flashing position light) introduction and thinning of service

The " management" of the core is quite an oddity
with Bedford delivery unit managing upto platform ramp at Farringdon (non conductor rail area)
and London Bridge delivery unit managing Farringdon platform and beyond (conductor rail area)
This excludes the overhead line which is managed to end of feed at City Thameslink by Bedford as Southern don't have overhead line team.

 

[GordonT]

Huge ammount of (rain) water fallen on entry to Smithfield sidings following roof work in connection with Museum of London building site which has taken over former Smithfield Market site, previous " dry" tunnel area now very damp directly around problem area causing PoSA signalling (flashing position light) introduction and thinning of service

The " management" of the core is quite an oddity
with Bedford delivery unit managing upto platform ramp at Farringdon (non conductor rail area)
and London Bridge delivery unit managing Farringdon platform and beyond (conductor rail area)
This excludes the overhead line which is managed to end of feed at City Thameslink by Bedford as Southern don't have overhead line team.

With hindsight would it have been better if there had always been an embargo on wires beyond St Pancras Thameslink heading south with the rest of the core and its sidings and beyond all 3rd rail?

 

[The exile]

With hindsight would it have been better if there had always been an embargo on wires beyond St Pancras Thameslink heading south with the rest of the core and its sidings and beyond all 3rd rail?

Other than the fact that the wires got to Farringdon several years before TL did.

 

[swt_passenger]

With hindsight would it have been better if there had always been an embargo on wires beyond St Pancras Thameslink heading south with the rest of the core and its sidings and beyond all 3rd rail?

If they’d have still wanted an AC/DC overlap between two suitable stations, (comparable to the current set up), to allow for reversal or recovery after random failures to change over, then the complex dual voltage area would have to either be far longer if between Farringdon and St Pancras, or far more complicated if it included the Canal Junctions area.

 

[Nicholas Lewis]

it’s all managed and controlled by the NR Southern Region, from Three Bridges. Maintenance from London Bridge depot, albeit the OLE is covered by the team in Bedford (And always has been).

the current track circuit issue is causing much head scratching. Most likely to be related to the third rail power system.

Thing is the service is holding up pretty well to time and you have to question why anything needs to be cancelled. The reality is with such low speed running through the core the investment in POSA's are showing there worth causing minimal delay and i guess drivers are expecting an issue so more prepared for them. So you have to wonder why the 9R's are being canned especially as Northbound and Southbound they have a 7m margin to following trains so are unlikely to delay anything.

 

[JaJaWa]

Second day in row that Thameslink up the swanny through the core due to ongoing signalling issues.

Very detailed explanation from Network Rail here:

Network Rail Kent & Sussex​

4h • 11 tweets
We’re really sorry for the ongoing disruption to @TLRailUK services north and south of London, owing to a problem with our signalling equipment between City Thameslink and Farringdon. Here’s what’s going on.../ /1

A “track circuit” that tells the signalling system where trains are has been failing intermittently for some time now. It operates fine for a while and then fails, putting an associated signal (red in the picture courtesy @traksyuk) to red and stopping trains. /2



This is a detailed look at where it is – called TDZ it controls access to Smithfield sidings and a signal too. It works by passing a low electric current through the rails and when a train runs over those rails (yellow) it short circuits the current. /3



The track circuit is isolated from the surrounding rails using insulated joints and we thought the problem was caused by metal swarf (shavings) that stick together, get picked up by train wheels and dropped over joints. /4



We cleared them, which helped, but it’s still failing and we are waiting for a gap in the train service to put monitoring equipment on the tracks to give us more data as to what is causing the problem. Every time we’ve investigated on site, the circuit has behaved perfectly. /5

It's a bit like when your car keeps putting a warning light up but you can't recreate it when the garage is looking at it. By logging data all day we can test our current hypothesis and then put a plan into action. /6

Tracks through this area have overhead power equipment and the live “third rail” – very rare - and it means the electrical connections are exceptionally complex. We’ve noticed the problem happens when trains heading north take power from the overhead lines at Farringdon. /7

So – tonight we’re going to switch the whole thing off and go through all the electrical connections to the rails, using data from today to guide us. It will mean overnight trains between Blackfriars and St Pancras will be disrupted, so please check before you travel. /8

In the meantime, we’ve locked the signal at red and “thinned” trains out through the section to reduce congestion. Trains are passing the red signal using a technique called “proceed on sight”, also unique to this section of track in this country. /9

Correction - not unique but unusual! It allows drivers to drive between certain signals "on sight" if they can see the track is clear between those signals. It's unusual as it requires special signals and training. /10

... and it takes longer, hence amending the train service to keep things flowing. We’re really sorry for the delays and disruption and we’re grateful for your ongoing patience with us. We’ll update you tomorrow – so until then please do check before you travel. /Ends

https://twitter.com/NetworkRailSE/status/1531938092457902085

 

[Bald Rick]

Thing is the service is holding up pretty well to time and you have to question why anything needs to be cancelled. The reality is with such low speed running through the core the investment in POSA's are showing there worth causing minimal delay and i guess drivers are expecting an issue so more prepared for them. So you have to wonder why the 9R's are being canned especially as Northbound and Southbound they have a 7m margin to following trains so are unlikely to delay anything.

don’t forget they are 2.5mins behind the 9V’s, which will be running late (around 3 mins), and therefore runn8ng late themselves before hitting the POSa

 

[SynthD]

When they have proceed on sight in a tunnel, do they add lighting?

 

[Nicholas Lewis]

don’t forget they are 2.5mins behind the 9V’s, which will be running late (around 3 mins), and therefore runn8ng late themselves before hitting the POSa

Assuming its a NB issue looking at OTT as stepping isn't happening 1054 to 1052 signals most NB trains are showing 2-3mins delay going NB on departing Farringdon since 1130(delays were being imported off an incident at Sydenham prior to then). Also my point was that there is then a 7min margin behind the 9R's so even if they end up 2-3mins down then there is then a firebreak in the schedule anyway through the core. If you wanted to avoid delays in the core you would take out something earlier but the 9R's are the convenient answer. At least they now seem to put the additional calls on 9J's as a matter of course mind you im expecting the 9R's to be culled anyhow to free up stock for Southern!

Lets see if they fix it overnight.

 

[swt_passenger]

Assuming its a NB issue looking at OTT as stepping isn't happening 1054 to 1052 signals most NB trains are showing 2-3mins delay going NB on departing Farringdon since 1130(delays were being imported off an incident at Sydenham prior to then). Also my point was that there is then a 7min margin behind the 9R's so even if they end up 2-3mins down then there is then a firebreak in the schedule anyway through the core. If you wanted to avoid delays in the core you would take out something earlier but the 9R's are the convenient answer. At least they now seem to put the additional calls on 9J's as a matter of course mind you im expecting the 9R's to be culled anyhow to free up stock for Southern!

Lets see if they fix it overnight.

NR‘s Twitter (copied and linked in post #12) seems to explain exactly where the faulty northbound track circuit is?

 

[thedbdiboy]

I remember reading about the very complex electrical arrangements needed to cope with both AC and DC circuits in a tunnel environment. Something to due with the presence of different metals in the circuitry, the damp and managing the risks of electrolytic corrosion.

 

[Nicholas Lewis]

NR‘s Twitter (copied and linked in post #12) seems to explain exactly where the faulty northbound track circuit is?

Oh thats very detailed from NR and that is certainly a awkward track circuit sitting over the S&C leading into Smithfield sidings. Need to get technical support in.

 

[jon0844]

You can be sure that despite the detailed explanation, social media and platforms will be full of 'pathetic' and 'feeble excuse' responses.

 

[Magdalia]

Assuming its a NB issue looking at OTT as stepping isn't happening 1054 to 1052 signals most NB trains are showing 2-3mins delay going NB on departing Farringdon since 1130(delays were being imported off an incident at Sydenham prior to then). Also my point was that there is then a 7min margin behind the 9R's so even if they end up 2-3mins down then there is then a firebreak in the schedule anyway through the core. If you wanted to avoid delays in the core you would take out something earlier but the 9R's are the convenient answer. At least they now seem to put the additional calls on 9J's as a matter of course mind you im expecting the 9R's to be culled anyhow to free up stock for Southern!

Lets see if they fix it overnight.

The key point is to prevent a queue of trains from forming. For that it is essential for the arrival rate to be kept below the processing rate. A track circuit failure (or, another recent example, a broken rail) adds to reoccupation time, thus lowering the processing rate, so cancelling trains is essential to keep the arrival rate below the processing rate. The gaps between individual trains in the timetable are irrelevant, what matters is the number of trains that can be accommodated in each 30 minute cycle, without a queue forming.

 

[Bald Rick]

Also my point was that there is then a 7min margin behind the 9R's so even if they end up 2-3mins down then there is then a firebreak in the schedule anyway through the core.

but the 9R is on minimum headway benhind the 9V. The latter loses 3 minutes, which means the 9R loses 3 minutes before it has even got to the affected section. It loses another 3 minutes, making it 6 minutes late, which makes the 9P following late, and so on.

Hence something has to come out to make it work and keep broadly to time. It’s all been tested desktop in the contingency planning that was done by one of the excellent TBROC controllers.

 

[Surreytraveller]

The key point is to prevent a queue of trains from forming. For that it is essential for the arrival rate to be kept below the processing rate. A track circuit failure (or, another recent example, a broken rail) adds to reoccupation time, thus lowering the processing rate, so cancelling trains is essential to keep the arrival rate below the processing rate. The gaps between individual trains in the timetable are irrelevant, what matters is the number of trains that can be accommodated in each 30 minute cycle, without a queue forming.

Indeed. The way I explain it to people is
If a train needs to be talked by (or is delayed for any reason), it may have a 2 minute delay. Which isn't an issue if there isn't a train behind
But if there's a train behind, that will be delayed by the first train's two minute delay, the have its own two minute delay, so that's four minutes.
Then the following train - four minutes then its own two minute delay.
And if the signaller is doing something else, like talking to S& T staff, they cannot talk a train past at the same time. Thinning a high frequency service is essential

 

[Minstral25]

but the 9R is on minimum headway benhind the 9V. The latter loses 3 minutes, which means the 9R loses 3 minutes before it has even got to the affected section. It loses another 3 minutes, making it 6 minutes late, which makes the 9P following late, and so on.

Hence something has to come out to make it work and keep broadly to time. It’s all been tested desktop in the contingency planning that was done by one of the excellent TBROC controllers.

But as regular user of 9R south of Croydon getting very fed up of regular service removal, haphazard replacement and weak platitudes from GTR. Service on route runs roughly 60% of the time, so users are very frustrated.
It’s time a different route takes a hit or a better solution found for cancellations especially when withdrawn for majoriy of the operational day.

 

[Surreytraveller]

But as regular user of 9R south of Croydon getting very fed up of regular service removal, haphazard replacement and weak platitudes from GTR. Service on route runs roughly 60% of the time, so users are very frustrated.
It’s time a different route takes a hit or a better solution found for cancellations especially when withdrawn for majoriy of the operational day.

There's alternative services, and stops are put on the Horshams for Earlswood and Salfords. Purley is a bit haphazard - sometimes the stops are put on, sometimes not. Which is a pain for people trying to get to Gatwick

 

[Gerald Fiennes]

Which really brings us back to the question of what the 9Rs are really for other than as a stepping stone in a long-standing master plan to get to the fabled 24tph through the core, ie. the Horshams to have the smaller stops (sorry, Purley!) 1tph and axe TL until commuter demand picks up enough to justify them? There's no shortage of capacity at the other end... Would save operating cost as well.....

 

[Surreytraveller]

Which really brings us back to the question of what the 9Rs are really for other than as a stepping stone in a long-standing master plan to get to the fabled 24tph through the core, ie. the Horshams to have the smaller stops (sorry, Purley!) 1tph and axe TL until commuter demand picks up enough to justify them? There's no shortage of capacity at the other end... Would save operating cost as well.....

They provide the required frequency of 4tph to Bedford.
They are a nuisance south of the Thames, as it means there's no direct service from Purley to Three Bridges or stations to Horsham, no direct service from Salfords or Earlswood to Merstham or Coulsdon, or stations to Horsham. They severely restrict travel opportunities in Surrey, replacing an all-stations service from London Bridge to Horsham that used to exist.

 

[DoubleLemon]

Very detailed explanation from Network Rail here:

https://twitter.com/NetworkRailSE/status/1531938092457902085

Thats a really good explanation and hope this sort of "good detail" that's but not full of jargon and where its needed it's explained. You can't beat a good analogy.

I once had to explain a database upgrade going wrong like a "wonky shelf that's coming out of the wall. Leave it alone and you can use it and take abd replace the odd item. Make changes to asll the items by moving them back and forth then its more likely the underlying issue (corruption in this I instance) would cause a faulure.

 

[Minstral25]

There's alternative services, and stops are put on the Horshams for Earlswood and Salfords. Purley is a bit haphazard - sometimes the stops are put on, sometimes not. Which is a pain for people trying to get to Gatwick

Not really, when you have a clock face timetabl you are supposed to turn up when your train is. The Horsham’s are on opposite quarter hours and they normally only stop alternate trains. So say you turn up on the hour for a normal service which is canned and then you have to wait 45 minutes for the replacement Horsham - your verdict is trains are poor. When that happens 2 out of 5 days every week there is a problem.

Earlswood and Salfords have often ended up with almost 3 hour gaps in service. Even Redhill 90 minute gaps because 9Js aren’t exactly reliable either.

Which really brings us back to the question of what the 9Rs are really for other than as a stepping stone in a long-standing master plan to get to the fabled 24tph through the core, ie. the Horshams to have the smaller stops (sorry, Purley!) 1tph and axe TL until commuter demand picks up enough to justify them? There's no shortage of capacity at the other end... Would save operating cost as well.....

9Rs (BED-GTW) really should have been all stations from Purley to Horsham and the 9Js (PBO-HOR) truncated at Gatwick as a fast service along Redhill route.

 

[JonathanH]

They severely restrict travel opportunities in Surrey, replacing an all-stations service from London Bridge to Horsham that used to exist.

At the same time the calling pattern spreads demand to London and offers faster off-peak services to London from the smaller stations than would exist if there was an all stations stopping train. In theory Redhill gets a better spacing of services to London as a result.

9Rs (BED-GTW) really should have been all stations from Purley to Horsham and the 9Js (PBO-HOR) truncated at Gatwick as a fast service along Redhill route.

I suspect that couldn't be timetabled given the Peterborough to Horsham train is right up behind the Bedford to Gatwick one when they reach Gatwick.

Why should Crawley and Horsham's service to London Bridge and Thameslink destinations be slow and unattractive though? It is all a balance, and that is arguably why the skip-stop pattern came about.

 

[Minstral25]

At the same time the calling pattern spreads demand to London and offers faster off-peak services to London from the smaller stations than would exist if there was an all stations stopping train. In theory Redhill gets a better spacing of services to London as a result..

You are making assumption only services to London matter. There are also many local journeys that need to be encouraged.

I suspect that couldn't be timetabled given the Peterborough to Horsham train is right up behind the Bedford to Gatwick one when they reach Gatwick.

Why should Crawley and Horsham's service to London Bridge and Thameslink destinations be slow and unattractive though? It is all a balance, and that is arguably why the skip-stop pattern came about.

Probably not, the original timetable was planned with Bedfords diverting to Reigate assuming completion of the now stalled/abandoned Platform 3 works.

However most Crawley Thameslink traffic gets on the train at Three Bridges (which is actually in Crawley) and there are much faster London Bridge service options than the Peterborough service. Horsham you can always get Arun Valley train and change for faster at East Croydon cross platform.