Fastest Absolute Block Line

[Economist]

A couple of years ago there was an interesting thread about the fastest single line section which I believe is/was 100mph. Does anyone know which section of track signalled using Absolute Block has/did have the highest linespeed? Back in the old days of steam, I believe there was a blanket speed restriction of 90mph on all lines except for specials etc. so this could possibly be the highest figure. Whilst I was taught the very basics of Absolute Block during my Rules training, I don't sign anywhere that's signalled using this method, so I'm not aware of a blanket speed which exists today other than the 125mph for Track Circuit Block.

 

[Senex]

I think the fastest ever was the old Western Region in the days when there was simply no maximum speed specified for the principal main lines—but I think that's going back more than 60 years!

 

[jfollows]

Ascott-under-Wychwood has some 90mph sections under AB if I interpret the Sectional Appendix correctly.

 

[jfollows]

100mph AB in Scotland, eg Easthaven LC (between Carnoustie and Arbroath)

 

[hexagon789]

I think the fastest ever was the old Western Region in the days when there was simply no maximum speed specified for the principal main lines—but I think that's going back more than 60 years!

An 80mph blanket was in place post war, lifted in 1955 to give no official maximum linespeed on four of its mainlines, then a 90mph limit was imposed in 1960 iirc.

Linespeed was then raised to 100 on some sections in 1966 for use with a pool of re-geared 37s worked in multiple on select Paddington-Bristol/South Wales services for a brief period before being replaced by Westerns and 47s, schedules were lengthened by 5 mins to accommodate.

 

[dk1]

An 80mph blanket was in place post war, lifted in 1955 to give no official maximum linespeed on four of its mainlines, then a 90mph limit was imposed in 1960 iirc.

Linespeed was then raised to 100 on some sections in 1966 for use with a pool of re-geared 37s worked in multiple on select Paddington-Bristol/South Wales services for a brief period before being replaced by Westerns and 47s, schedules were lengthened by 5 mins to accommodate.

Fascinating stuff. Thank you.

 

[godfreycomplex]

100mph AB in Scotland, eg Easthaven LC (between Carnoustie and Arbroath)

Indeed - 100mph at various points (not sure exactly where) between Dunblane and Aberdeen. Also a brief cameo on the Highland Main Line.
In the murky world of signalling standards 100mph is the cutoff for a lot of things. Any line with a line speed higher than that must be continuously track circuited with colour light signals (I’m fairly sure 3 or 4 aspect is needed), and all level crossings must be controlled (that is to say, not automatic).
God I’m a nerd...

 

[Senex]

An 80mph blanket was in place post war, lifted in 1955 to give no official maximum linespeed on four of its mainlines, then a 90mph limit was imposed in 1960 iirc.

Linespeed was then raised to 100 on some sections in 1966 for use with a pool of re-geared 37s worked in multiple on select Paddington-Bristol/South Wales services for a brief period before being replaced by Westerns and 47s, schedules were lengthened by 5 mins to accommodate.

Do you happen to know when the war-time 60 went up to 80 — and was that Western only (I seem to remember the LM having a general 75 for main lines before the 90 came back (or 80 on some sections of the Midland lines))?
I wonder if anyone has the actual wording from the Western WTTs for those five years of no limit. Was it something like "may run as fast as is required"?
Somewhere I think I've still got a log of a pre-service publicity run with the 2 37s and the XP64 set from Paddington to Bristol. It was quite a run!

 

[Senex]

Found it! See Michael Clemens's railways site
http://www.michaelclemensrailways.co.uk/?atk=576
and the Western Region passenger WTT for winter 1958-9 page A184:

 

[Peter C]

Ascott-under-Wychwood has some 90mph sections under AB if I interpret the Sectional Appendix correctly.

Ascott does have some 90mph sections, yes - and I believe that it's only a viable contender here because of the equipment it uses to interface with Moreton-in-Marsh 'box, but I might be wrong.

-Peter

 

[hexagon789]

Do you happen to know when the war-time 60 went up to 80 — and was that Western only (I seem to remember the LM having a general 75 for main lines before the 90 came back (or 80 on some sections of the Midland lines))?
I wonder if anyone has the actual wording from the Western WTTs for those five years of no limit. Was it something like "may run as fast as is required"?
Somewhere I think I've still got a log of a pre-service publicity run with the 2 37s and the XP64 set from Paddington to Bristol. It was quite a run!

It was pretty much something like, "speed may be as high as required to maintain the schedules" or something similar. To be fair it seemed possible maintain even the tighter booking without exceeding about 80-85, most logs of the late-50s/early-60s have trains cruising in the low 80s mostly.

 

[hexagon789]

Found it! See Michael Clemens's railways site
http://www.michaelclemensrailways.co.uk/?atk=576
and the Western Region passenger WTT for winter 1958-9 page A184:

View attachment 79657

Brilliant, I couldn't remember the website which had a selection of old WR WTTs, so thanks for finding it!

 

[Senex]

It was pretty much something like, "speed may be as high as required to maintain the schedules" or something similar. To be fair it seemed possible maintain even the tighter booking without exceeding about 80-85, most logs of the late-50s/early-60s have trains cruising in the low 80s mostly.

And that ties in nicely with a slightly later WTT on the same site, for the Birmingham District, summer 1962, where on page H3 it says explicitly that timings were designed to be kept without continuous use of full power (which brings us to the fascinating question of how a recovery allowance is best provided). Here's the relevant bit of H3:


The last paragraph seems like a pretty good statement of what could still be regarded today as good train working!

 

[30907]

Indeed - 100mph at various points (not sure exactly where) between Dunblane and Aberdeen. Also a brief cameo on the Highland Main Line.
In the murky world of signalling standards 100mph is the cutoff for a lot of things. Any line with a line speed higher than that must be continuously track circuited with colour light signals (I’m fairly sure 3 or 4 aspect is needed), and all level crossings must be controlled (that is to say, not automatic).
God I’m a nerd...

The ECML was largely mechanically signalled and AB when the Deltics were first permitted 100mph - and stayed that way in places!

 

[hexagon789]

And that ties in nicely with a slightly later WTT on the same site, for the Birmingham District, summer 1962, where on page H3 it says explicitly that timings were designed to be kept without continuous use of full power (which brings us to the fascinating question of how a recovery allowance is best provided). Here's the relevant bit of H3:

View attachment 79664
The last paragraph seems like a pretty good statement of what could still be regarded today as good train working!

Indeed, no point flooring it only to be stuck waiting at a station for an extra few minutes time and again

 

[Economist]

Thank you all for the replies so far on this thread, I imagine a ton under AB, in particular semaphores (if they're still around), would be interesting. Unfortunately I've only ever seen AB in action on a whiteboard/video, where I drive it's all TCB.

 

[Tomnick]

Thank you all for the replies so far on this thread, I imagine a ton under AB, in particular semaphores (if they're still around), would be interesting. Unfortunately I've only ever seen AB in action on a whiteboard/video, where I drive it's all TCB.

We’ve got a bit of 90mph AB (with semaphores) on our routes and honestly it’s not as bad as some folk make out, especially if you’ve got colour light distants. If you’ve got the distant off, then you’re all good. If you’ve got the distant on, then the speed becomes irrelevant once you’ve got the brake in, as long as you know where the home signal is. Picking it out at night or in fog can be ‘interesting’, but as I say the speed’s gone by that stage and there’s no rush, and all that remains is to remember which one’s the section signal!

If it’s AB with colour lights, you wouldn’t really know the difference if you’d not read it in the sectional appendix!

 

[craigybagel]

Shrewsbury - Little Mill (just north of Pontypool) is entirely AB, other then for a few miles in the middle between Moreton-on-Lugg and Hereford. Line speed varies but there are several 90 mph sections, so I suspect those are the joint fastest in both Wales and England.
Also in Wales the North Wales coast is still AB West of Llandudno Junction, and there is a bit of 90mph between there and Bangor.
In England I believe the Hope Valley line is still AB, and that has 90mph sections.

 

[jfollows]

90mph AB around Llanfairfechan on the North Wales coast, I'd missed that one!
Plenty of SP90 on the Hope Valley.