Regulating decisions on Thameslink

[Class15]

Hi all,

This is not the first time I’ve been screwed by strange regulating decisions on the Thameslink route, and I’m sure it won’t be the last. My regular train, 9O21 St Albans City - Sutton, is regularly held at West Hampstead Thameslink for up to 7 minutes to allow the late-running 9L87 Bedford - East Grinstead service to take its slot in front. If you ask me, this is too long, but I understand why this is done to protect the order of trains in the core.

What I don’t understand is what happened this morning. After a 5 minute delay at West Hampstead, we were subsequently held again, this time for only a minute or so, outside St Pancras to allow the on-time 9S09 Cambridge - Brighton to pass in front. Now this doesn’t sound too bad but remember the amount of slack in the core, time lost which 9O21 was unable to regain due to the fact that 9S09 in front was on time and 9O21 was being held before every station to wait for 9S09 to leave.

So what’s the difference between West Hampstead and St Pancras? I just don’t understand the reasoning for favouring late-runners at one and on-time trains at the other. And both times with 9O21 being at the receiving end of the delays.

Can anyone explain this for me?

 

[43055]

Different signallers on different routes. West Hampstead is controlled from West Hampstead box whereas St Pancras is Three Bridges I think.

With 9L87 being on the fast line there is also a possibility that a EMR or two is right behind so giving it a clear run keeps things flowing better and as you say right order for the core might be a consideration as well.

 

[43074]

This is not the first time I’ve been screwed by strange regulating decisions on the Thameslink route, and I’m sure it won’t be the last. My regular train, 9O21 St Albans City - Sutton, is regularly held at West Hampstead Thameslink for up to 7 minutes to allow the late-running 9L87 Bedford - East Grinstead service to take its slot in front. If you ask me, this is too long, but I understand why this is done to protect the order of trains in the core.

9L87 (0703 Bedford to East Grinstead) starts from Bedford at a particularly busy time of the morning peak, where units are entering service from the various sidings there, so it's a pretty congested time of the morning and more often than not is late starting from Bedford.

7' late at West Hampstead with a good run through the core is usually recoverable to 3 or 4 mins late by New Cross Gate thanks to the various timetable allowances which apply to trains either side of the core - in the grand scheme of things it's easier to manage a train presenting 3' late at Croydon than one which is 7' late.

In the case of the 9Sxx, if that runs late to Brighton then it risks carrying delay with it to a late start for it's next working - it would be quite plausible for this delay to be rippling through the system 3/4 hours later given interactions these services have through Croydon, the core (a couple of hours later), Welwyn viaduct and in the Cambridge area itself.

The Sutton loop services are comparatively easy to recover delay from by skip stopping - not ideal but can prevent delays carrying too far - whereas the longer distance TL routes are much harder to recover due to the sheer complexities of the interactions they have en-route.

 

[Wychwood93]

The 9O21 has a 2 minute turnaround at Sutton platform 2, arriving at 0847 and departing back to St Albans with the 9O22 at 0849!

See RTT: https://www.realtimetrains.co.uk/se...UO/2025-10-08/0847?stp=WVS&show=all&order=wtt

The 9S07 is booked into platform 7 at Brighton at 0848 - the next working from 7 is the 0928 9T16 to Bedford. Obviously the same stock! Little chance for the 9S07 to import delay into its next working!

See RTT: https://www.realtimetrains.co.uk/search/detailed/gb-nr:BTN/2025-10-09/0848

 

[Horizon22]

The 9O21 has a 2 minute turnaround at Sutton platform 2, arriving at 0847 and departing back to St Albans with the 9O22 at 0849!

See RTT: https://www.realtimetrains.co.uk/se...UO/2025-10-08/0847?stp=WVS&show=all&order=wtt

It's not really a "turnaround" though - it continues going forward 'anticlockwise' on the Sutton loop. Just a different headcode so it doesn't form one single "St Albans - St Albans" train and is instead split.

== Doublepost prevention - post automatically merged: 9 Oct 2025 ==

What I don’t understand is what happened this morning. After a 5 minute delay at West Hampstead, we were subsequently held again, this time for only a minute or so, outside St Pancras to allow the on-time 9S09 Cambridge - Brighton to pass in front. Now this doesn’t sound too bad but remember the amount of slack in the core, time lost which 9O21 was unable to regain due to the fact that 9S09 in front was on time and 9O21 was being held before every station to wait for 9S09 to leave.

Considering the train was 5L at Kentish Town and then 4L at St Pancras, this didn't cause any major issue.

Seems like this was probably ARS keeping the on-time train, on-time. Or the TOC requested the "main line" train to be routed ahead, possibly due to conflicts south of London Bridge.

 

[Class15]

Considering the train was 5L at Kentish Town and then 4L at St Pancras, this didn't cause any major issue.

Seems like this was probably ARS keeping the on-time train, on-time. Or the TOC requested the "main line" train to be routed ahead, possibly due to conflicts south of London Bridge.

Had 9O21 been routed ahead of 9S09, 9O21 would have ended up at Blackfriars around 2 minutes late. 9S09 immediately following would also have been around 2 minutes late. 2 minutes for 9S09 can easily be made up due to allowances before and after London Bridge. It’s much harder to recover a 5 minute delay.

Different signallers on different routes. West Hampstead is controlled from West Hampstead box whereas St Pancras is Three Bridges I think.

With 9L87 being on the fast line there is also a possibility that a EMR or two is right behind so giving it a clear run keeps things flowing better and as you say right order for the core might be a consideration as well.

This makes sense - I doubt 9L87 would actually have been held at West Hampstead (9O21 due out at 07:47, 9L87 ended up there at 07:51), but probably would have got stuck behind 9O21 at either Kentish Town or St Pancras - so I understand this.

9L87 (0703 Bedford to East Grinstead) starts from Bedford at a particularly busy time of the morning peak, where units are entering service from the various sidings there, so it's a pretty congested time of the morning and more often than not is late starting from Bedford.

7' late at West Hampstead with a good run through the core is usually recoverable to 3 or 4 mins late by New Cross Gate thanks to the various timetable allowances which apply to trains either side of the core - in the grand scheme of things it's easier to manage a train presenting 3' late at Croydon than one which is 7' late.

In the case of the 9Sxx, if that runs late to Brighton then it risks carrying delay with it to a late start for it's next working - it would be quite plausible for this delay to be rippling through the system 3/4 hours later given interactions these services have through Croydon, the core (a couple of hours later), Welwyn viaduct and in the Cambridge area itself.

The Sutton loop services are comparatively easy to recover delay from by skip stopping - not ideal but can prevent delays carrying too far - whereas the longer distance TL routes are much harder to recover due to the sheer complexities of the interactions they have en-route.

Again, this makes a lot of sense - but not sure about 9S09’s return working causing issues. It seems to have a decent turnaround at Brighton of around 25 minutes. However, absolutely realise that the BML (Brighton Main Line) is very congested and that would cause issues there.

 

[Horizon22]

Had 9O21 been routed ahead of 9S09, 9O21 would have ended up at Blackfriars around 2 minutes late. 9S09 immediately following would also have been around 2 minutes late. 2 minutes for 9S09 can easily be made up due to allowances before and after London Bridge. It’s much harder to recover a 5 minute delay.

It did OK, being 1L by Tulse Hill and 2L by Sutton, which may have been good luck more than anything else!

 

[Magdalia]

Another example of Thameslink controllers being criticised for good regulation.

The southbound morning peak is Thameslink's most intensive service. There are 11 southbound trains through St Pancras in a 30 minute period:

0745 9J09 Peterborough-Horsham
0747 9K11 Luton-Orpington
0750 9T11 Bedford-Brighton
0755 9L87 Bedford-East Grinstead
0757 9O21 St Albans-Sutton
0800 0S09 Cambridge-Brighton
0802 9P11 Luton-Rainham
0805 9R05 Flitwick-Three Bridges
0807 9Y13 Welwyn GC-Sevenoaks
0810 9T81 Bedford-Three Bridges
0812 9V23 St Albans-Sutton
0815 9J11 Peterborough-Horsham

I have highlighted in bold those that pass through East Croydon, a train every 5 minutes. The potential knock on effects of delays at East Croydon are big so it makes sense to give priority to keeping time on the trains heading towards East Croydon.

That's what happened

[9O21] did OK, being 1L by Tulse Hill and 2L by Sutton

and without a significant delay on the Sutton loop.

 

[Bald Rick]

Hi all,

This is not the first time I’ve been screwed by strange regulating decisions on the Thameslink route, and I’m sure it won’t be the last. My regular train, 9O21 St Albans City - Sutton, is regularly held at West Hampstead Thameslink for up to 7 minutes to allow the late-running 9L87 Bedford - East Grinstead service to take its slot in front. If you ask me, this is too long, but I understand why this is done to protect the order of trains in the core.

What I don’t understand is what happened this morning. After a 5 minute delay at West Hampstead, we were subsequently held again, this time for only a minute or so, outside St Pancras to allow the on-time 9S09 Cambridge - Brighton to pass in front. Now this doesn’t sound too bad but remember the amount of slack in the core, time lost which 9O21 was unable to regain due to the fact that 9S09 in front was on time and 9O21 was being held before every station to wait for 9S09 to leave.

So what’s the difference between West Hampstead and St Pancras? I just don’t understand the reasoning for favouring late-runners at one and on-time trains at the other. And both times with 9O21 being at the receiving end of the delays.

Can anyone explain this for me?

I was on (a very busy) 9L87 that morning. I was somewhat surprised to see 9O21 held at W Hampstead, but also pleased. We were 8 mins late of St Albans, and with that regulating decision and some proper driving (and ATO) we were back on time at London Bridge. That was the best run I have ever had on a southbound Thameslink from St Albans, in about 4,000 trips.

At St Pancras, 9O21 was evidently held because 9S09 presented at the junction first. But I agree, with the allowances south of the core it would have made more sense to send you on first, as you would both have been back on time by Herne Hill / New Cross Gate respectively. However the decision for the signaller was a little more in favour of 9S09 - It was a case of delaying you by a further minute or the Cambridge by 2 mins.

Seems like this was probably ARS keeping the on-time train, on-time.

No ARS at either workstation involved.

 

[Class15]

I was on (a very busy) 9L87 that morning. I was somewhat surprised to see 9O21 held at W Hampstead, but also pleased. We were 8 mins late of St Albans, and with that regulating decision and some proper driving (and ATO) we were back on time at London Bridge. That was the best run I have ever had on a southbound Thameslink from St Albans, in about 4,000 trips.

At St Pancras, 9O21 was evidently held because 9S09 presented at the junction first. But I agree, with the allowances south of the core it would have made more sense to send you on first, as you would both have been back on time by Herne Hill / New Cross Gate respectively.

Very good post. Thank you very much. Yes, with the allowances I think the perfect solution is to hold 9O21 for 9L87 but not for 9S09 in that kind of scenario. Also agreed that the Thameslink drivers can be very quick about runs down through the core, but some drivers seem to wait until the whole ‘we will be calling at…’ is finished until leaving!

 

[Horizon22]

No ARS at either workstation involved.

Not even at Canal Tunnel Junction? Seems like a very busy section without ARS?

 

[Bald Rick]

Not even at Canal Tunnel Junction? Seems like a very busy section without ARS?

Nope!