Single lead junction for Scarborough line at York

toby_farman · 20 Oct 2019

Moderators note: Split from https://www.railforums.co.uk/threads/shortest-section-of-single-track.193303/

Greetlander said:
I took this screenshot from the excellent cabview video from Don Coffey (and if you're on here Sir, I apologise for the theft and salute your excellent films).

It's the "single lead junction" across Scarborough Bridge at York. It has me wondering if the section between the points qualifies as a single line, and if so, is there a shorter section anywhere else?

They have doubled it

On google earth, they seem to have doubled it...

RailUK Forums

Darandio · 20 Oct 2019

toby_farman said:
On google earth, they seem to have doubled it...

They haven't doubled it, it's hidden in those trees at the top of your image.

najaB · 20 Oct 2019

Darandio said:
They haven't doubled it, it's hidden in those trees at the top of your image.

Indeed. The sectional appendix still shows a single lead junction:

toby_farman · 20 Oct 2019

Darandio said:
They haven't doubled it, it's hidden in those trees at the top of your image.

What's the point in not doubling? I mean, i don't know why it's there but it can't be that expensive to double it up

najaB · 20 Oct 2019

toby_farman said:
I mean, i don't know why it's there but it can't be that expensive to double it up

If you take a look at the page from the sectional appendix that I posted above it's a cheap junction to provide access to both platforms and the exam siding.

ElectroSoldier · 20 Oct 2019

toby_farman said:
What's the point in not doubling? I mean, i don't know why it's there but it can't be that expensive to double it up

hahah

If you double up the infrastructure you double up the cost. That is why they started to lean towards leading junctions 30 odd years ago or more.
It was all about cutting costs.

Consider what is involved in replacing that leading junction.
I mean really think about what is involved in ripping it up and putting in a new switch that allows access to the mainline, station and sidings one way and the main line the other.

edwin_m · 21 Oct 2019

ElectroSoldier said:
Consider what is involved in replacing that leading junction.
I mean really think about what is involved in ripping it up and putting in a new switch that allows access to the mainline, station and sidings one way and the main line the other.

In principle it ought to be just two set of switches and a bit of track to connect them, plus signaling changes which shouldn't be too horrendous considering it's a SSI area. That's unless there is some problem with the supporting formation in the area where the track would go back, or something else like a load of signaling equipment or cables in the way.

rower40 · 21 Oct 2019

toby_farman said:
What's the point in not doubling? I mean, i don't know why it's there but it can't be that expensive to double it up

But for what benefit? There's only one train per hour to/from Scarborough, and the only parallel move would be to allow a down train to depart York platform 5 towards Scarborough while an up train comes off the Scarborough line into York platforms 4 or 3 or 2. Most trains to Scarborough depart from platform 4 anyway (keeping platform 5 available for ECML moves), so making Scarborough Bridge Junction double-lead doesn't really add to the flexibility of the layout, or any reduction in delay.

<edit to add...>
<Penny drops...>
The bridge over the river has two tracks over it. But because the junction is single-lead, there can never be two trains on the bridge at the same time. So the bridge doesn't have to be strengthened. If the junction were doubled, then the bridge would be subject to a whole new regime of loading-calculations and inspections and what-not.

GingerSte · 21 Oct 2019

rower40 said:
But for what benefit? There's only one train per hour to/from Scarborough, and the only parallel move would be to allow a down train to depart York platform 5 towards Scarborough while an up train comes off the Scarborough line into York platforms 4 or 3 or 2. Most trains to Scarborough depart from platform 4 anyway (keeping platform 5 available for ECML moves), so making Scarborough Bridge Junction double-lead doesn't really add to the flexibility of the layout, or any reduction in delay.

<edit to add...>
<Penny drops...>
The bridge over the river has two tracks over it. But because the junction is single-lead, there can never be two trains on the bridge at the same time. So the bridge doesn't have to be strengthened. If the junction were doubled, then the bridge would be subject to a whole new regime of loading-calculations and inspections and what-not.

The bridge gas been strengthened recently (I think).

ElectroSoldier · 21 Oct 2019

realaledrinker said:
Interesting thread. Will make sure i have a good look next time I'm passing!

edwin_m said:
In principle it ought to be just two set of switches and a bit of track to connect them, plus signaling changes which shouldn't be too horrendous considering it's a SSI area. That's unless there is some problem with the supporting formation in the area where the track would go back, or something else like a load of signaling equipment or cables in the way.

Every switch is bespoke.
Then you want to:
Give a train from Scarborough access to both platforms 2, 4 and 5 at York so you have to add a right hand facing switch otherwise all you have access to is 2 & 4. Then its the same the other way around, so you have how it looks in the sectional appandix track view but with a little line linking up the Up Scarborough to York, but in reality what you have done is added twice the amount of new infrastructure...
You havent added a short strip of track to link up the two lines you have replaced two sets of switches with two sets of switches, added a piece of track and the signalling updates to support it all...
And the benefit is... You now have exactly the same operational ability as you did before, but this time it costs more to look after it... Oh and then you have to figure you will have twice as much load on the bridge so you will need to factor that into the costs of it all too.

rower40 said:
But for what benefit? There's only one train per hour to/from Scarborough, and the only parallel move would be to allow a down train to depart York platform 5 towards Scarborough while an up train comes off the Scarborough line into York platforms 4 or 3 or 2. Most trains to Scarborough depart from platform 4 anyway (keeping platform 5 available for ECML moves), so making Scarborough Bridge Junction double-lead doesn't really add to the flexibility of the layout, or any reduction in delay.

<edit to add...>
<Penny drops...>
The bridge over the river has two tracks over it. But because the junction is single-lead, there can never be two trains on the bridge at the same time. So the bridge doesn't have to be strengthened. If the junction were doubled, then the bridge would be subject to a whole new regime of loading-calculations and inspections and what-not.

Couldnt have said it better myself.

It reminds me of the situation of reinstating Halton Junction at Runcorn.
There used to be a flat junction there that caused is no end of problems for decades and eventually lead to it being removed. in favor of a single line from Halton jn to Frodsham Jn.
Then when they reinstated it they did it as a lead... It raised some eyebrows as if to say its been done in the cheap... Its not when you look at it that while it has been cheaper there is no real good reason to do otherwise when the current service pattern and plans dont over use the infrastructure and you lower the costs of maintenance along the way too.

swt_passenger · 21 Oct 2019

GingerSte said:
The bridge gas been strengthened recently (I think).

It has, in fact the bridge decks were completely renewed only around 4 years ago, as shown in this video:

As I wrote in the parent thread (where the original quoted section first appeared), I think that the original poster was using the phrase “across the bridge” to mean “the other side of the bridge”.

I’m firmly of the opinion now that the reason for the single lead Junction has nothing to do with the bridge.

ElectroSoldier · 21 Oct 2019

It doesnt really matter about the bridge though does it, when you consider all that work adds nothing.

edwin_m · 21 Oct 2019

Aren't Northern supposed to be adding an extra service every hour to Scarborough at some point?

On checking I find there's a signal 235 in the Down direction only, between the station throat and the single line. But it looks to be so close to the station that I'm not sure how many cars could be standing at it before they block the diamond and prevent any moves into or out of the north end of platforms 2 or 5. If the longest likely train (presume a 1+5 Nova 3 in future, longer than the existing 3-car 185) can wait at this signal without blocking anything, then the operational benefit of doubling would indeed be small because a Scarborough-bound train could be got out of the station even if it then had to wait for the single line. However if there isn't that amount of standage then the single line effectively makes the station junction a single lead for capacity purposes.

ElectroSoldier · 21 Oct 2019

Singnal 235 in at the end of platform 4.
Once signal 235 is cleared it signals a move onto the bridge and over onto the leading junction. A move that stops mid route would foul the switch into platform 2.
a move from 217 signal that comes to a stop mid route would indeed stand on the diamond blocking a route into the station from the north...

However having said that looking at the map I would say that signal 217 is not only the junction signal that clears a route over the diamond but also over the leading junction the other side of the bridge as the next signal is number 1 on the Bootham Crossing....
Would that mean that that signal acts as the section signal... and the next set is not under the control of the same box?

If a train standing in the station has to wait for a path over the single line then you would not clear the signal even if there was another signal section between it and the single section.

AS you say making the junction a single lead has benefits of its own as it limits outside the station.

Booked platforms is 4 from Scarborough and platform 5 towards.

Northern si an interesting one thats for sure...
An extra service wont make any difference really.
It might be a problem for traffic from the north into York P4 when they want to leave P5

edwin_m · 21 Oct 2019

ElectroSoldier said:
Singnal 235 in at the end of platform 4.
Once signal 235 is cleared it signals a move onto the bridge and over onto the leading junction. A move that stops mid route would foul the switch into platform 2.
a move from 217 signal that comes to a stop mid route would indeed stand on the diamond blocking a route into the station from the north...

However having said that looking at the map I would say that signal 217 is not only the junction signal that clears a route over the diamond but also over the leading junction the other side of the bridge as the next signal is number 1 on the Bootham Crossing....
Would that mean that that signal acts as the section signal... and the next set is not under the control of the same box?

If a train standing in the station has to wait for a path over the single line then you would not clear the signal even if there was another signal section between it and the single section.

AS you say making the junction a single lead has benefits of its own as it limits outside the station.

Booked platforms is 4 from Scarborough and platform 5 towards.

Northern si an interesting one thats for sure...
An extra service wont make any difference really.
It might be a problem for traffic from the north into York P4 when they want to leave P5

There is an error in the Five Mile Diagram I was looking at, 235 is indeed the platform starter from P4 towards Scarborough. The next signal towards Scarborough is S1, a two-aspect stop signal presumably controlled by Strensall. The routes in both directions lead over both the station throat and the single lead so a train would not normally stop between the two.

So it's not possible for a train to Scarborough to be signalled to leave platform 5 at the same time as one from Scarborough is signalled to arrive in platform 2 or 4. If the overlap from 234 (south end of P4) runs over 801 points into P3 then re-doubling the single line and changing the timetable so Scarborough trains passed each other here would permit one extra path every hour from the north into P4. I don't know whether this would be significant for station capacity.

ElectroSoldier · 21 Oct 2019

edwin_m said:
There is an error in the Five Mile Diagram I was looking at, 235 is indeed the platform starter from P4 towards Scarborough. The next signal towards Scarborough is S1, a two-aspect stop signal presumably controlled by Strensall. The routes in both directions lead over both the station throat and the single lead so a train would not normally stop between the two.

So it's not possible for a train to Scarborough to be signalled to leave platform 5 at the same time as one from Scarborough is signalled to arrive in platform 2 or 4. If the overlap from 234 (south end of P4) runs over 801 points into P3 then re-doubling the single line and changing the timetable so Scarborough trains passed each other here would permit one extra path every hour from the north into P4. I don't know whether this would be significant for station capacity.

I know. Im pretty sure thats what I told you...

I would like to know how you calculate that doubling the track there would open up an extra path per hour...
Is that based on line headway at that single pinch point or the diagraming on a new service that precludes a service right now as they would clash there at that junction at that time?

edwin_m · 21 Oct 2019

ElectroSoldier said:
I know. Im pretty sure thats what I told you...

I would like to know how you calculate that doubling the track there would open up an extra path per hour...
Is that based on line headway at that single pinch point or the diagraming on a new service that precludes a service right now as they would clash there at that junction at that time?

The move from the north into platform 3 conflicts with the move from platform 4 towards Scarborough. If the overlap is as I described then a train coming into platform 4 from Scarborough will also lock the points between platform 4 and platform 3 and therefore prevent a move from the north into platform 3, until it has come to a stand in platform 4 and the overlap times out. Hence with the current layout, where trains can't depart towards and arrive from Scarborough at the same time, Scarborough moves block the move from the north into platform 3 twice every hour.

With the single section doubled and a different timetable it would be possible (in theory) for both those Scarborough moves to happen at the same time, so the move into platform 3 from the north would only be blocked once every hour and one more train in each hour could make that move. If the Scarborough service was increased to 2TPH then the doubling of the single lead could lead to two more paths into platform 3, or rather losing one path less than would otherwise be the case.

ElectroSoldier · 21 Oct 2019

Yeah..... I see. I was under the impression that the way it actually works is.
Platform 3 and 4 are contiguous. with 4 being the north end and 3 being the south end.
The signal protecting the platform from Scarborough is 272, when cleared it gives access to platform 4 but does not give direct access to platform 3
The signal protecting the platform from the north is 304, when cleared it gives access to platform 3
Half way along the platform is signal 236. while 232 is at the end of platform 3.

So you can route from Scarborough from 272 to 236 and route a train from 304 to 232 at the same time. Not so?

A move from York towards Scarborough from platform 5 would indeed stop signal 304 being cleared to signal 232 as they conflict.
To solve that all you would really have to do is swap platforms... and route the Scarborough bound train over platforms 3 and 4 and into the branch and the south bound train onto platform 5 with a move from 304 to 228 then over the left hand facing switch to 204 signal.

Basically a train can approach from the north and path and a train can approach from Scarborough and path at the same time.
As far as I know anyway

edwin_m · 21 Oct 2019

ElectroSoldier said:
So you can route from Scarborough from 272 to 236 and route a train from 304 to 232 at the same time. Not so?

I suspect not but I'd need a full signaling plan to check. I only have the Five Mile Diagram which shows signals but not other details such as overlaps, and as well as the error I mentioned above I've just noticed it has two signals numbered 234 - so I'll assume the one controlling access from P2 to P3 is 236 as you state. There may be other errors too... fortunately people don't use this plan as a definitive source of information!

A main signal route normally locks the track not just from the entry signal to the exit signal but for a distance beyond the exit signal, known as the overlap, as a safety margin in case the train slips by the signal. If, as I suspect, the overlap beyond 236 goes through 801 points then a route up to 236 would also lock 801 and therefore prevent a train running into P3 via 304 signal at the same time. However this may not be so, or there may be a reduced overlap route which allows a train to approach but leaves 801 free, in which case the driver would see a delayed yellow at 272. If there is an overlap then it is released by a timer, freeing 801 points, once the track circuit in P2 has been occupied long enough that the train must have come to a stop or at least is going very slowly.

ElectroSoldier · 21 Oct 2019

The arrangement on those two platforms gives a great deal of operational flexibility...
What with the diagram the way it is right now there is no need to open up that leading junction.

beverleyonian · 21 Oct 2019

As a user of the line, the biggest improvement IMHO would be to reinstate one of the centre roads between platforms 3 and 5 so a southbound train at platform 4 is not blocked by one at platform 3, as happens not infrequently.

ElectroSoldier · 22 Oct 2019

beverleyonian said:
As a user of the line, the biggest improvement IMHO would be to reinstate one of the centre roads between platforms 3 and 5 so a southbound train at platform 4 is not blocked by one at platform 3, as happens not infrequently.

That I could understand and would be a better use of money.

Right now as I write there is a train signalled from 272 into platform 4, while a south bound train was signalled from 304 over to platform 9. then another southbound is signalled into platform 5 right behind it all while platform 3 is occupied with a freight. and now while 1A60 is cleared from 304 into P5 1F56 is being signalled into platform 4...

swissrailpassion · 22 Oct 2019

It was a scissors. What the station lacks is a through road. The 1990s re-design restricts capacity. Many were very surprised the through lines were dispensed with. Harrogate bays were cut back to 1 when two platforms would be more useful today.

ElectroSoldier · 23 Oct 2019

There are relief lines to the west of the station from Holgate jn to Skelton Jn

edwin_m · 23 Oct 2019

ElectroSoldier said:
There are relief lines to the west of the station from Holgate jn to Skelton Jn

Indeed. However southbound freight often runs through the station to avoid crossing over the fast lines at Skelton and back again somewhere south of Holgate.

ElectroSoldier · 23 Oct 2019

edwin_m said:
Indeed. However southbound freight often runs through the station to avoid crossing over the fast lines at Skelton and back again somewhere south of Holgate.

Yeah south bound is an operational problem...
A relief between 3/4 and 5 would be better and keep through trains off the fast lines.

edwin_m · 23 Oct 2019

ElectroSoldier said:
Yeah south bound is an operational problem...
A relief between 3/4 and 5 would be better and keep through trains off the fast lines.

Probably so but I think the geometry of the crossing of the line that comes across between 3 and 4 would be very tricky. It would be a curved diamond or possibly a ladder junction on a curve, and possibly result in lower speed and more maintenance.

In the long term it's probably better to replace the flat crossing by the Up Slow at Skelton Bridge with a flyover. Most of the freight goes via Church Fenton not via the Selby Diversion, and by using this flyover and the avoiding lines it could avoid any conflict with the main fast lines all the way through the York area.

ElectroSoldier · 24 Oct 2019

Or put a right hand facing switch into the track that puts you into platform 3 to allow a train to carry on rather that visit 3 as it is now?

edwin_m · 24 Oct 2019

ElectroSoldier said:
Or put a right hand facing switch into the track that puts you into platform 3 to allow a train to carry on rather that visit 3 as it is now?

That might make platform 3 too short to fit an 80x between the fouling point of the new turnout and the south end of the platform.

ElectroSoldier · 24 Oct 2019

It depends on what you are looking to achieve.
If you want a relief line more than a route away from 3 without being routed into 4 or the other way around.
Platform 3 is rather long. The best but most expensive would be a sissor cross over. Its compact and works well but maintenance is very high on them.

Single lead junction for Scarborough line at York

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