When to Switch? Holborn Fasts to Slows (and vice versa)

[SE%Traveller]

I have a question of I was hoping some of the knowledgeable folks on this site might help me with and that is why the trains on the Holborn lines cross from fast to slow where they do.

As I understand it on the UP there are 3 opportunities to cross from Slows to Fasts: Loughborough Junction, Elephant & Castle, Blackfriars; and 2 opportunities to cross from Fasts to Slows: Loughborough Junction, Blackfriars. On the Down It’s the opposite (2 from Slow to Fast, 3 from Fast to Slow).

Now with a background in contingency planning and mitigating risks (But no Rail knowledge) I would have thought best practice would be to switch trains at the first opportunity so if you couldn’t complete the switch for whatever reason you could try again at the next set junction. Therefore optimally trains would change:
On the Up: Loughborough Junction
On the Down: Blackfriars

However, all the Suttons do the opposite and change at Blackfriars on the Up and Loughborough Junction on the Down.
The Sevenoaks Service do change at Loughborough Junction on the UP but on the Down they too change at Loughborough Junction.
The Orpington’s don’t normally need to change lines.

Is there some operational need I’m completely missing? I understand that what I’m calling Blackfriars Blackfriars Junction is South of the Junction with the Metropolitan Curve so conflicting with London Bridge Trains not an issue.
Aside from anything else it would be nice if all trains heading to Catford departed from Elephant from the same platform. It’s a long old trudge from Platform 2 to 4…

NB In the Peaks even the Sevenoaks makes the switch on the UP to the Slows at Blackfriars. But perhaps this is historical as the Beckenham Junctions used to run into Platform 4 at Blackfriars on or around the time the Sevenoaks ran into Platform 3 so this only physically possible by making the switch there. Or for that matter future proofing as they’re supposed to be a through train in the peaks so no switching required….

Anyway grateful for anyone who can help answer or correct any of the above for that matter

 

[30907]

Just to clarify: the Slows are the westernmost pair of tracks.

 

[Timmyd]

No idea about the answer but as a daily user it's a great question I'd love to know the answer to. Southbound platforming at the Elephant is always a lottery and never seems to be a logic behind it

 

[greatkingrat]

There is no particular reason why crossing moves should always be done at the first opportunity. Points failures aren't that common that you need to design the whole timetable around the possibility of one occurring. More important is when there are suitable gaps in the trains coming the other way so you can cross over without delaying other trains. Of course, on a complex route like Thameslink, there will often be trains running a few minutes late, and hence the signallers may find it more convenient to cross the train over at a different location to usual when there is a gap.

 

[Peregrine 4903]

Your missing Southwark Bridge Junction too which is another place you can cross.

Too be honest, there isn't really a particular logic behind it. The fact is, the current timetable doesn't really have enough traffic for all 4 tracks to actually be required most of the time, meaning there is plenty of capacity to cross the trains wherever.

The only time I would say there is a much larger pattern and greater variance for crossing moves is when Thameslink services that normally run via London Bridge, run via Herne Hill and where trains cross from the fast lines to the slow lines and vice versa is much more critical.

 

[SE%Traveller]

Just to clarify: the Slows are the westernmost pair of tracks.

Yep sorry should have specified!

== Doublepost prevention - post automatically merged: 15 Dec 2021 ==

Your missing Southwark Bridge Junction too which is another place you can cross.

Too be honest, there isn't really a particular logic behind it. The fact is, the current timetable doesn't really have enough traffic for all 4 tracks to actually be required most of the time, meaning there is plenty of capacity to cross the trains wherever.

The only time I would say there is a much larger pattern and greater variance for crossing moves is when Thameslink services that normally run via London Bridge, run via Herne Hill and where trains cross from the fast lines to the slow lines and vice versa is much more critical.

Yeah I'm sure you're right on the traffic point. But if there is no operational reason to do it this way Then it would be Better for passengers if they could at least make all the Catfords stop at Platform 4 (Fast Down E Side). The Orpington's share all but two stops with the Sevenoaks trains after alll

 

[IrishDave]

The short answer is: parallel moves.

If the trains were to cross at the first available opportunity, then the path taken would conflict with the train going in the opposite direction, as seen in the diagram below (for simplicity, I've just shown two possible crossing points).



By crossing them later, they can run in parallel, meaning that they can be timetabled more freely and aren't tied together. (I suppose there's an argument for them crossing at the *same* junction, but as late as possible works just fine!)

Of course, the opposite logic would apply if the situation were mirrored (e.g. trains between Denmark Hill and the bay platforms at Blackfriars) - there trains would ideally cross as early as possible, again to give parallel moves.

 

[Bald Rick]

I have a question of I was hoping some of the knowledgeable folks on this site might help me with and that is why the trains on the Holborn lines cross from fast to slow where they do.

As I understand it on the UP there are 3 opportunities to cross from Slows to Fasts: Loughborough Junction, Elephant & Castle, Blackfriars; and 2 opportunities to cross from Fasts to Slows: Loughborough Junction, Blackfriars. On the Down It’s the opposite (2 from Slow to Fast, 3 from Fast to Slow).

Now with a background in contingency planning and mitigating risks (But no Rail knowledge) I would have thought best practice would be to switch trains at the first opportunity so if you couldn’t complete the switch for whatever reason you could try again at the next set junction. Therefore optimally trains would change:
On the Up: Loughborough Junction
On the Down: Blackfriars

However, all the Suttons do the opposite and change at Blackfriars on the Up and Loughborough Junction on the Down.
The Sevenoaks Service do change at Loughborough Junction on the UP but on the Down they too change at Loughborough Junction.
The Orpington’s don’t normally need to change lines.

Is there some operational need I’m completely missing? I understand that what I’m calling Blackfriars Blackfriars Junction is South of the Junction with the Metropolitan Curve so conflicting with London Bridge Trains not an issue.
Aside from anything else it would be nice if all trains heading to Catford departed from Elephant from the same platform. It’s a long old trudge from Platform 2 to 4…

NB In the Peaks even the Sevenoaks makes the switch on the UP to the Slows at Blackfriars. But perhaps this is historical as the Beckenham Junctions used to run into Platform 4 at Blackfriars on or around the time the Sevenoaks ran into Platform 3 so this only physically possible by making the switch there. Or for that matter future proofing as they’re supposed to be a through train in the peaks so no switching required….

Anyway grateful for anyone who can help answer or correct any of the above for that matter

it removes conflicts; if you cross at first opportunity you will be crossing the traffic coming the other way.

I gather that, at last, Southwark Bridge Junction is going to be plain lined.

 

[Peregrine 4903]

it removes conflicts; if you cross at first opportunity you will be crossing the traffic coming the other way.

I gather that, at last, Southwark Bridge Junction is going to be plain lined.

Oh no, that's sad. I presume it must be a maintenance nightmare or some other issue for it to be plain lined. It was a useful Junction to have particularly from an STP perspective.

 

[4-SUB 4732]

Right outside Loughborough Junction you can make all moves.

Southwark Bridge junction is slow to fast northbound, fast to slow southbound.

Blackfriars Junction is all moves.

So there’s two chances for any move to be made, but Southwark Bridge is selective.

 

[Bald Rick]

Oh no, that's sad. I presume it must be a maintenance nightmare or some other issue for it to be plain lined. It was a useful Junction to have particularly from an STP perspective.

It’s difficult to keep together, and three junctions doing the same thing in about 2.5 miles is an extravagance.

 

[SE%Traveller]

Well thanks for the info, good to know some reasoning behind why some things are done the way they are. If the traffic light though, still think it would be nice to have platform certainly on the southbound direction at Elephant. Perhaps they'll look at it again when Sevenoaks hooks tup to Welwyn as i presume they'll stay on the fasts all the way once coming through the core...

 

[Stephen42]

Well thanks for the info, good to know some reasoning behind why some things are done the way they are. If the traffic light though, still think it would be nice to have platform certainly on the southbound direction at Elephant. Perhaps they'll look at it again when Sevenoaks hooks tup to Welwyn as i presume they'll stay on the fasts all the way once coming through the core...

A Sevenoaks coming through the core would stay on the fast as it would only create more conflicts to go to the slows. The Orpington and Sevenoaks services pass each other at Blackfriars Junction which is why the southbound Sevenoaks services can't cross at Blackfriars Junction.

 

[SE%Traveller]

Yep during the Peaks they wouldn't need to cross at all, it's only when the in the off peaks they go into the bays that the the Sevenoaks service needs to cross. That said i was on one the other day which crossed fasts to slows at Loughborough Junctions before then going back to the fasts at Blackfriars and the detrained at 2 with both bays empty. I guessed they must have been taking it to the sidings or something

 

[Bald Rick]

Yep during the Peaks they wouldn't need to cross at all, it's only when the in the off peaks they go into the bays that the the Sevenoaks service needs to cross. That said i was on one the other day which crossed fasts to slows at Loughborough Junctions before then going back to the fasts at Blackfriars and the detrained at 2 with both bays empty. I guessed they must have been taking it to the sidings or something

That would have been some disruption. Possibly a failure of Southwark bridge junction.

 

[zwk500]

Oh no, that's sad. I presume it must be a maintenance nightmare or some other issue for it to be plain lined. It was a useful Junction to have particularly from an STP perspective.

It's a maintenance nightmare as it's in the middle of 4 tracks on top of a viaduct and moving all the crossing moves to either Loughborough Jn or Blackfriars actually showed a very slight improvement to the performance of the timetable.

 

[Bald Rick]

It's a maintenance nightmare as it's in the middle of 4 tracks on top of a viaduct and moving all the crossing moves to either Loughborough Jn or Blackfriars actually showed a very slight improvement to the performance of the timetable.

Switch diamonds as well IIRC.

 

[Snow1964]

It's a maintenance nightmare as it's in the middle of 4 tracks on top of a viaduct and moving all the crossing moves to either Loughborough Jn or Blackfriars actually showed a very slight improvement to the performance of the timetable.

Were the middle set a hangover from the days of Walworth coal sidings (coal drops), allowing trains to get around slower trains entering the sidings, and allow a clock face timetable

 

[zwk500]

Were the middle set a hangover from the days of Walworth coal sidings (coal drops), allowing trains to get around slower trains entering the sidings, and allow a clock face timetable

I have absolutely no idea, I'm afraid. It may also be a hangover from the old layout of Blackfriars with the bays on the east, as Blackfriars Jn would have prioritised crossing trains from London Bridge to the western pair of tracks.

 

[ComUtoR]

I gather that, at last, Southwark Bridge Junction is going to be plain lined.

Noooooooo

One of my favourite junctions.

 

[SE%Traveller]

I have absolutely no idea, I'm afraid. It may also be a hangover from the old layout of Blackfriars with the bays on the east, as Blackfriars Jn would have prioritised crossing trains from London Bridge to the western pair of tracks.

IIRC during the rebuilding of Blackfriars everything made the move to the fasts there on the UP. going Down only the Wimbledon's did. The Mitchams did it at Loughborough Junction. Later at night i think it was used more so (as i learned on these forums ) only platforms 2/3 needed to be served. BY the time it came to the London Bridge rebuild i think Blackfriars was favoured. Another advantage of changing early is that passengers who may have been suffering from Poor Train Selection Syndrome get earlier notice of such and can change. there was nothing worse on an evening journey home than a sudden lurch to the right at Loughborough Junction followed by a 'this is now running fast to Bromley South' to make an evening. (to be fair most would stop at one or other of Loughborough Junction or Herne Hill where the trip home is not that much longer than Denmark Hill)

 

[norbitonflyer]

Back in the dark days of the early 1980s, when the service really was run down, in the off peak all up services from the Herne Hill direction crossed over at the "first" opportunity, crossing back just before Blackfriars to use the through platforms (then on the west side). Similarly, all down Blackfriars-Catford Loop services crossed over to the western pair just after Blackfriars, crossing back before Loughborough Junction. With only 4tph on the four track section, it was rare for there to be a conflict, but I can only assume the extra wear and tear on the points was worth it to achieve the staff savings of only using the island platform at Elephant.

 

[SE%Traveller]

Back in the dark days of the early 1980s, when the service really was run down, in the off peak all up services from the Herne Hill direction crossed over at the "first" opportunity, crossing back just before Blackfriars to use the through platforms (then on the west side). Similarly, all down Blackfriars-Catford Loop services crossed over to the western pair just after Blackfriars, crossing back before Loughborough Junction. With only 4tph on the four track section, it was rare for there to be a conflict, but I can only assume the extra wear and tear on the points was worth it to achieve the staff savings of only using the island platform at Elephant.

yep that was the practice i was thinking of, but at the time it was just late at night. for a period after the rebuild the Sevenoaks.Service was ran by SE out of the bays from 9pm onwards in any event whilst it was still a joint service with FCC. when the latter took it over they ran it from West Hampstead Thameslink

 

[4-SUB 4732]

I have absolutely no idea, I'm afraid. It may also be a hangover from the old layout of Blackfriars with the bays on the east, as Blackfriars Jn would have prioritised crossing trains from London Bridge to the western pair of tracks.

This is how I remember it coming into its own, as it allowed peak stuff from the likes of Chatham and Maidstone via Herne Hill to those 3 bays.

 

[SE%Traveller]

That would have been some disruption. Possibly a failure of Southwark bridge junction.

Yeah it seemed odd at them time. I only recall a couple of occasions it terminating at platform 2 and then both bays were definitely full, they usually hold it at Elephant if one isn't free. I do once remember being held there at Platform 3 and being 'undertook' by the Orpington service which sneaked past on the slows....