125mph with 3-aspect colour light signalling

[Wilts Wanderer]

Something I find interesting about the GWML is the extent of the route that has 3-aspect signalling. Of the 125mph-linespeed sections, I believe 3-aspect signalling is in place on everything west of Tilehurst, including such complex layouts as Didcot and Swindon.

Without ATP, I would not like to be a driver travelling at these speeds with only one yellow aspect before the red. One badly timed sneeze or other distraction could have undesirable results. I do find it surprising that the unions were willing to accept this arrangement when HSTs were introduced in the 1970s, although I know BR made much of the braking capability compared to traditional loco and coaching stock.

Are there any other 125mph routes with anything other than 4-aspect signalling? (Ignoring HS1.)

 

[Jonny]

Something I find interesting about the GWML is the extent of the route that has 3-aspect signalling. Of the 125mph-linespeed sections, I believe 3-aspect signalling is in place on everything west of Tilehurst, including such complex layouts as Didcot and Swindon.

Without ATP, I would not like to be a driver travelling at these speeds with only one yellow aspect before the red. One badly timed sneeze or other distraction could have undesirable results. I do find it surprising that the unions were willing to accept this arrangement when HSTs were introduced in the 1970s, although I know BR made much of the braking capability compared to traditional loco and coaching stock.

Are there any other 125mph routes with anything other than 4-aspect signalling? (Ignoring HS1.)

I believe there may be sections of the ECML north of Newcastle... However, that may have changed in recent years.

Edit: a few sections appear here

at about the 9:40 mark (a 125mph limit sign promptly followed by a 3-aspect signal).

 

[Ianno87]

Trying to remember if the route between Colwich and Stone via Hixon is
A) 125mph
B) 3 aspect signalled (certainly used to be)

 

[furnessvale]

Something I find interesting about the GWML is the extent of the route that has 3-aspect signalling. Of the 125mph-linespeed sections, I believe 3-aspect signalling is in place on everything west of Tilehurst, including such complex layouts as Didcot and Swindon.

Without ATP, I would not like to be a driver travelling at these speeds with only one yellow aspect before the red. One badly timed sneeze or other distraction could have undesirable results. I do find it surprising that the unions were willing to accept this arrangement when HSTs were introduced in the 1970s, although I know BR made much of the braking capability compared to traditional loco and coaching stock.

Are there any other 125mph routes with anything other than 4-aspect signalling? (Ignoring HS1.)

Surely the same applies on 4 aspect signalling. One badly timed sneeze and miss the double yellow, the first thing you see is the single yellow and again it is too late.

 

[Darandio]

One badly timed sneeze or other distraction could have undesirable results.

Except if they had sneezed past a yellow aspect they would have acknowledged an AWS warning. If they had a green the signal previously then they know they have just passed a yellow and brake accordingly. If they are still somehow unsure (unlikely) then i'd expect them to act as though they had a cautionary aspect.

Regardless of this it's extremely unlikely anyway given the vast majority of signals are sighted for a few seconds beforehand, it would need to be a lengthy sneeze.

 

[43096]

Surely the same applies on 4 aspect signalling. One badly timed sneeze and miss the double yellow, the first thing you see is the single yellow and again it is too late.

Quite. I’m not sure the OP has grasped that signal sections are longer in 3 aspect areas than 4 aspect areas for the same line speed.

 

[Warwick]

I bet he didn't/hadn't.

 

[AndrewE]

Quite. I’m not sure the OP has grasped that signal sections are longer in 3 aspect areas than 4 aspect areas for the same line speed.

and so it is cheaper to install - but cuts capacity by increasing headways. Long sections (to accommodate higher speed, when we only run at 125mph) are the curse of the WCML.

 

[ac6000cw]

The primary reason for installing 4 aspect signalling is to increase line capacity, by allowing trains to run closer together (albeit at reduced speed when very busy).

 

[12guard4]

One badly timed sneeze you aren't missing a yellow because you have AWS.

 

[AndrewE]

The primary reason for installing 4 aspect signalling is to increase line capacity, by allowing trains to run closer together (albeit at reduced speed when very busy).

And the other side of the coin is...? Install 3-aspect (save 25% of signal section costs) and cut capacity.

 

[Robsignals]

And the other side of the coin is...? Install 3-aspect (save 25% of signal section costs) and cut capacity.

The busy West Coastway Brighton - Worthing is largely 3-aspect designed for 100 mph to reduce the number of signals though line speed is 70 mph. It's 4-aspect at each end where stoppers and limited stops are close together and features around Worthing and West Worthing require it and still max speed would be 75 mph.

 

[Kneedown]

Midland Main line between Sileby and Leicester has a stretch of 120mph linespeed on three aspect. Very "character building" coming around the bend at Sileby on an HST and seeing a yellow in front of you, and also the red at Syston in the distance. As it happens there is plenty of room, and you've not quite got up to 120, but still not the best of feelings.

 

[superhands]

As someone said above 4 aspect means more trains 3 aspect means higher speeds. On the up and down Badminton most of the signal sections are two miles long (apart). It's all based on line speed.

 

[Taunton]

If I remember correctly the section Didcot-Swindon, at least, was just 2-aspect at the start of the 125 era. Distants, and then stop signals, were at the approximate spacings that the later 3-aspects were, and were changed later as increased capacity was required.

It is of course extremely straight and two signals ahead being visible applies on a fair bit. It had been a typical mid-1960s WR minimalist installation.

 

[driver_m]

Yes via Hixon is 125mph (EPS only though) and has 3 aspect signalling.. It's not an issue as the signal sections are much longer than normal and being a fairly quiet line, you very rarely encounter a single yellow.

 

[bionic]

London underground signalling is two aspect with repeaters (distants) only provided for badly sighted signals. I know line speeds are far lower but at certain locations the driver has very little reaction time indeed. They also have no AWS, TPWS or DRA and the train stop system only intervenes when it's too late. A very different world from the one upstairs.

 

[AndrewE]

IEdit: a few sections appear at about the 9:40 mark (a 125mph limit sign promptly followed by a 3-aspect signal).

It might be worth mentioning that nowadays the physical appearance of the signal head can be misleading. in the 1960s when the WCML was modernised it was clear that pretty well all the signals were 4-aspect because they had 4 lenses and hoods. Nowadays with LEDs you can have several colours in what looks like a single "lens", so a single one can be red, yellow or green and you only need a second to display a double yellow.

 

[Wilts Wanderer]

Just for the record I’m aware of how braking distances are set up in respect to 3 and 4 aspect signalling, so no need for any of the smug comments. However I’m interested in the psychology of having one yellow aspect rather than two. As Kneedown says, it is ‘character building’!

 

[driver_m]

Because it's so rare to get one yellow on that stretch at Hixon, you certainly sit up and take notice, but it's covered in our rules anyway, to change braking technique when encountering rarer cautionary aspects. But there's actually worse places to get an unexpected double yellow. Mainly because the sections are short. Wolverton used to be the worst one (near Milton Keynes) as it needed a heavy brake application. (Now alleviated by having a green banner repeater to give more warning to us if on yellows).

 

[AndrewE]

Just for the record I’m aware of how braking distances are set up in respect to 3 and 4 aspect signalling, so no need for any of the smug comments. However I’m interested in the psychology of having one yellow aspect rather than two. As Kneedown says, it is ‘character building’!

...but perhaps not so aware of the AWS horn (or its modern equivalent) and the visual indicator/reminder that you have just passed a signal with a restrictive aspect. The horns used to be deafening, especially if you were an extra person stood up in the cab with your back to the engine-room bulkhead!

 

[Wilts Wanderer]

No... I am fully aware of the AWS horn as well!

It’s off the end of the 125 stretch, but a single yellow on the 100mph at Bathford approaching Bathampton Jcn usually produces a brake application sufficient to knock a cup of coffee over. The poor sighting of the signals and very short (approx 1.5 mile) section has long been hated by drivers.

 

[EE Andy b1]

Trying to remember if the route between Colwich and Stone via Hixon is
A) 125mph
B) 3 aspect signalled (certainly used to be)

Yep 125mph EPS (Enhanced Permissible Speed), max 95mph PS (Permissible Speed).

Still 3 aspect signalling.

 

[AndrewE]

No... I am fully aware of the AWS horn as well!

It’s off the end of the 125 stretch, but a single yellow on the 100mph at Bathford approaching Bathampton Jcn usually produces a brake application sufficient to knock a cup of coffee over. The poor sighting of the signals and very short (approx 1.5 mile) section has long been hated by drivers.

Surely a banner repeater is needed then. Is there still any mechanism for formal driver feedback or for the union to make representations on it? I would think that if the need (well recognised by those best qualified to judge it) is in writing somewhere then the "management" in its broadest sense would be on a loser if they ever tried to criticise a driver in that area.

 

[Wilts Wanderer]

I have no idea, and to be honest wasn’t really the point of the thread. More interested in what stretches of 125mph railway have 3-aspect signalling. I’ve often wondered why ATP is seen to be required on GWML and not other high speed routes, and whether 3-aspect signalling is the factor.

 

[Taunton]

An interesting thread where both spellings of "siting" and "sighting" are relevant.

I think the main reason for ATP on the GW Main is that it was the pioneer trial installation, it was allowed to fall into disuse, Southall happened, it was rapidly reactivated for all, there was criticism in the official report, and nobody can bring themselves to step back from it. With good reason.

If the ATP reactivation had been done fully Ladbroke Grove would not have happened.

London underground signalling is two aspect with repeaters (distants) only provided for badly sighted signals.

On the faster open air sections repeaters are constantly provided, generally termed "Fog repeater" and labelled as such on the unit. The Piccadilly on the nonstop bit from Hammersmith to Acton Town, for example, has these continually, to the extent that sometimes three or more signals ahead are visible at once. They run all the time, not just in fog.

 

[AndrewE]

On the faster open air sections repeaters are constantly provided, generally termed "Fog repeater" and labelled as such on the unit. The Piccadilly on the nonstop bit from Hammersmith to Acton Town, for example, has these continually, to the extent that sometimes three or more signals ahead are visible at once. They run all the time, not just in fog.

...so are these things red railway signals that can actually be passed at danger without a calling on aspect? Just a note that it is a repeater - which must be unique to LU! I believe BR introduced banner repeaters precisely so that there would never be a situation where a conventional signal was passed at danger without a special authorisation.

 

[pt_mad]

When the HSTs were introduced in the GWML, wern't two drivers required at all times up until the early 1990s?

Required over 110mph if I'm correct?

 

[The Planner]

and so it is cheaper to install - but cuts capacity by increasing headways. Long sections (to accommodate higher speed, when we only run at 125mph) are the curse of the WCML.

Eh? The WCML runs at 3 minute headways south of Crewe and is probably capable of it for a fair bit north of there to Preston and onwards. It is mixed traffic that knackers the WCML.

 

[AndrewE]

Eh? The WCML runs at 3 minute headways south of Crewe and is probably capable of it for a fair bit north of there to Preston and onwards. It is mixed traffic that knackers the WCML.

True, but I believe it was designed for 140mph. Signals spaced closer for 125mph might allow 2 1/2 minute headways, nearly a 20% increase in capacity.