How long is too long for an absolute block section and where is the longest?

507020

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Since the closure of Bescar Lane and New Lane signal boxes near Southport in the 1990s, there has only been a single absolute block section between the ML148 signal on the approach to Meols Cop station and the BB2 signal at Burscough Bridge station. On Saturday, a Southport - Stalybridge service was held at Southport station until a late running Alderley Edge service in front (which doesn’t stop at certain stations and so had to be sent first) had cleared the ML148 signal, but was then held at the ML148 signal itself until the train in front had cleared the BB2 signal a distance of roughly 7 miles away! When held at this signal, trains aren’t even able to proceed as far as Meols Cop station, a much more sensible place to wait.

It is not unsafe for a train to proceed onto a line where the next train is 7 miles in front of it, so my question is, is this simply too long for the section to be and what are the longest ones in Britain. Is this one of them?
 
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MadMac

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I believe the longest is Settle Junction-Carnforth at over 20 miles! Dunblane-Blackford is of a similar length to your example and does cause problems, although there are moves afoot to get the intermediate box at Greenloaning back up and running to split the section. The question of “how long should the section be” comes down to how many trains you typically want to run in a given timeframe.
 

507020

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I believe the longest is Settle Junction-Carnforth at over 20 miles! Dunblane-Blackford is of a similar length to your example and does cause problems, although there are moves afoot to get the intermediate box at Greenloaning back up and running to split the section. The question of “how long should the section be” comes down to how many trains you typically want to run in a given timeframe.
How many trains you typically want to run in a given timeframe is irrelevant, as there are a whole host of reasons why you might want more trains to run in a given timeframe than that, a simple delay as in my example is one of them. Where is the resiliency now?

Of course between Settle Junction and Carnforth there was originally also Wennington Junction for Lancaster Green Ayre and the hilariously named Clapham Junction for the Ingleton Line, so this section would have been too long when they were still open.
 

Gloster

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Not so many years ago Hungerford worked with Heywood Road Junction at Westbury on a Sunday, which was just under thirty-three miles. At night there was the single line from Wilton South to Yeovil Junction, which was just over thirty-six miles.
 

Tomnick

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Burscough Bridge works TCB to Sandhills - it's not an absolute block section.
 

Ken H

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when they were rebuilding the WCML for electrification in the 60's, it was said (in jest) trains were signalled county to county rather than block to block!
 

Annetts key

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Cost of opening an extra signal box vs. resignalling vs. paying out if the cause is determined to be Network Rail…
Guess which wins…

So yes, the length is determined by the planned / required line capacity.
 

Ken H

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Cost of opening an extra signal box vs. resignalling vs. paying out if the cause is determined to be Network Rail…
Guess which wins…

So yes, the length is determined by the planned / required line capacity.
and then there is intermediate block....
 
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Cost of opening an extra signal box vs. resignalling vs. paying out if the cause is determined to be Network Rail…
Guess which wins…

So yes, the length is determined by the planned / required line capacity.
At the risk of kicking the hornets nest here - With modern technology surely there's a better solution?
 

The Planner

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How many trains you typically want to run in a given timeframe is irrelevant, as there are a whole host of reasons why you might want more trains to run in a given timeframe than that, a simple delay as in my example is one of them. Where is the resiliency now?

Of course between Settle Junction and Carnforth there was originally also Wennington Junction for Lancaster Green Ayre and the hilariously named Clapham Junction for the Ingleton Line, so this section would have been too long when they were still open.
How much resilliance do you factor in, where do you stop, at what point does the cost outweigh the benefits?
 

Journeyman

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I believe the longest is Settle Junction-Carnforth at over 20 miles! Dunblane-Blackford is of a similar length to your example and does cause problems, although there are moves afoot to get the intermediate box at Greenloaning back up and running to split the section. The question of “how long should the section be” comes down to how many trains you typically want to run in a given timeframe.
Has Greenloaning not reopened yet? They were recruiting for it a couple of years ago. Sadly I wasn't successful.
 

Ken H

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How much resilliance do you factor in, where do you stop, at what point does the cost outweigh the benefits?
Thats a business decision, surely. A massive delay because of a long section means the railway suffers reputational loss. How you calculate the value of that I dont know.
On another thread we see a discussion about Northerns TVM's. There is speculation about whether cost cutting had made the TVM system vulnerable. Whether northern now regret that cost cutting in view of the disruption to their business to the outage I cant say.
 
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Since the closure of Bescar Lane and New Lane signal boxes near Southport in the 1990s, there has only been a single absolute block section between the ML148 signal on the approach to Meols Cop station and the BB2 signal at Burscough Bridge station. On Saturday, a Southport - Stalybridge service was held at Southport station until a late running Alderley Edge service in front (which doesn’t stop at certain stations and so had to be sent first) had cleared the ML148 signal, but was then held at the ML148 signal itself until the train in front had cleared the BB2 signal a distance of roughly 7 miles away! When held at this signal, trains aren’t even able to proceed as far as Meols Cop station, a much more sensible place to wait.

It is not unsafe for a train to proceed onto a line where the next train is 7 miles in front of it, so my question is, is this simply too long for the section to be and what are the longest ones in Britain. Is this one of them?
Yes it is unsafe as allowing another train into an absolute block section contravenes the fundamental rule of absolute block: one train in one section at one time!
Where the signals are placed though is a different question and there quite possibly are better places for signals to assist with keeping the passenger service running. There is always the option of adding intermediate block signals to sub divide a section, but the cost of that would have to be weighed against the cost of delays/or benefits that splitting the section can bring in purely financial terms.
 

Annetts key

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yes. ETCS Level 2.
Yep. But this only makes financial sense if the trains are ETCS fitted… Otherwise it’s more costly than a handful of LED colour light signals, the required track circuits or axle counters and minimal interlocking plus the required cables.

So you have to weigh up how much each proposed solution would cost overall.
 

pdeaves

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It is not unsafe for a train to proceed onto a line where the next train is 7 miles in front of it
Do you know the previous train is 7 miles away, or do you suspect it is based on what normally happens? That's how absolute block works - you don't send the next train into the section until the previous one has left. The signallers have no visibility on what's going on until the train reaches them. You resignal if you need more visibility and/or increased frequency.
 

jopsuk

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Yep. But this only makes financial sense if the trains are ETCS fitted… Otherwise it’s more costly than a handful of LED colour light signals, the required track circuits or axle counters and minimal interlocking plus the required cables.

So you have to weigh up how much each proposed solution would cost overall.
They asked if there was a solution using modern technology! They didn't ask about the cost
 

Dr Hoo

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Are there any single track sections longer than that? Some on the Far North line look to be close to 20 miles.
When the Radio Electronic Token Block was first designed it was possible to combine multiple movement authorities into 'long section' working. (I think that it is now limited to two sections at most.) So, at least in theory, at night it would have been possible to issue one authority for (say) Dingwall to Georgemas Junction for a freight.

(Obviously in practical terms it would usually be broken up to allow for things like local track patrolling and maintenance possessions.)
 

ChiefPlanner

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LLandrindod to Craven Arms was one , until the loop at Knighton (not much used TBF) was out back in......
 

Welshman

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Do you know the previous train is 7 miles away, or do you suspect it is based on what normally happens? That's how absolute block works - you don't send the next train into the section until the previous one has left. The signallers have no visibility on what's going on until the train reaches them. You resignal if you need more visibility and/or increased frequency.
Reminiscent of the old bobby on the end of the platform with an egg-timer.
"Well, its been all of 15 minutes now - must be safe to start this one"
 

Falcon1200

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Not much of an issue with the frequency of service, though.

It is nowadays ! (Or at least was pre-Covid). The Far North Line service is more intense now than ever, with as well as the four Wick/Thurso through trains, various short workings. It got to the stage that if the afternoon northbound Wick was late, it would be held for around an hour to avoid delaying the afternoon southbound Wick, because if the latter was late, its crossings with other trains, conflict with the Kyle line trains, and turnround times would wreck the Far North and Kyle line timetable for the rest of the day; Whereas the northbound caused no such issues.
 

Jonny

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I believe the longest is Settle Junction-Carnforth at over 20 miles! Dunblane-Blackford is of a similar length to your example and does cause problems, although there are moves afoot to get the intermediate box at Greenloaning back up and running to split the section. The question of “how long should the section be” comes down to how many trains you typically want to run in a given timeframe.

How many trains you typically want to run in a given timeframe is irrelevant, as there are a whole host of reasons why you might want more trains to run in a given timeframe than that, a simple delay as in my example is one of them. Where is the resiliency now?

Of course between Settle Junction and Carnforth there was originally also Wennington Junction for Lancaster Green Ayre and the hilariously named Clapham Junction for the Ingleton Line, so this section would have been too long when they were still open.

Has Greenloaning not reopened yet? They were recruiting for it a couple of years ago. Sadly I wasn't successful.

An alternative might be to put intermediate block equipment in at, or somewhere near, Greenloaning. The business case should consider and, if possible, quantify timetable recovery as well as any increases in capacity.
 

craigybagel

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LLandrindod to Craven Arms was one , until the loop at Knighton (not much used TBF) was out back in......
Pre Covid trains crossed there every morning.

Sometimes even resignalling isn't the answer. When Nantwich - Shrewsbury was resignalled in 2013, it went from Absolute Block to TCB controlled from Cardiff - but the old AB sections were replicated, meaning there is still a near 10 mile section between Prees and Wrenbury which limits how close the local service can follow the fast, and adds to delays when trains are running late.

There was a box half way along that section at Whitchurch, but it closed a few years before resignalling, and the opportunity to replace it wasn't taken up.
 

The Planner

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Pre Covid trains crossed there every morning.

Sometimes even resignalling isn't the answer. When Nantwich - Shrewsbury was resignalled in 2013, it went from Absolute Block to TCB controlled from Cardiff - but the old AB sections were replicated, meaning there is still a near 10 mile section between Prees and Wrenbury which limits how close the local service can follow the fast, and adds to delays when trains are running late.

There was a box half way along that section at Whitchurch, but it closed a few years before resignalling, and the opportunity to replace it wasn't taken up.
I think its been said on here before, but that resignalling was a shocker.
 

scrapy

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The Southport line has another long absolute block section from Parbold to just before Wigan sidings. Unless both are resignalled, the train wll just end up waiting at Parbold anyway.

The long block sections can cause problems at peak times, when 3 trains an hour use the line as one delay causes a knock on, add in the railhead treatment train that often runs in the afternoon peak during leaffall and delays can mount, whether or not it's worth the cost of resignalling, I'm not sure.
 

MadMac

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An alternative might be to put intermediate block equipment in at, or somewhere near, Greenloaning. The business case should consider and, if possible, quantify timetable recovery as well as any increases in capacity.
I believe one of the driving factors is to get it back in with longer loops to accommodate freight.
 

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