Colour Light Signals - Light Order

[MarkyT]

No, it is double blocking - in all cases a freight stood at the signals protecting North Jn would hang back across the level crossings on approach, which the double blocking prevents.

That makes total sense, although I thought there was some additional double blocking originally associated with junction risk that was removed when or sometime after TPWS was added.

 

[edwin_m]

The double blocking is very much still there (and related to the level crossings).

The other thing to remember is that the majority of moves on the junction are to/from Peterborough (the fully doubled route), even with doubling both King's Lynn and Norwich lines, you still end up with quite a few "conventional" conflicts left.

If the other two legs were doubled and trains timetabled to pass on the junction, you'd get one extra path to and from Peterborough for each pair of paths to and from Norwich or Lynn.

Did the former 20mph apply to the Peterborough route? If so then there is some benefit from the higher speed which partly or fully offsets the disbenefit of the single lead. However that isn't always the case - for the examples I mentioned at Euxton and Wigston the doubling was done by adding the extra track but leaving the former single lead in place, so the speed for the route that causes most conflict won't have changed.

 

[Ianno87]

If the other two legs were doubled and trains timetabled to pass on the junction, you'd get one extra path to and from Peterborough for each pair of paths to and from Norwich or Lynn.

But the nature of Ely is that will, to some extent, have presentation times dictated to it by what suits the rest of the network, not what suits Ely.

Did the former 20mph apply to the Peterborough route? If so then there is some benefit from the higher speed which partly or fully offsets the disbenefit of the single lead. However that isn't always the case - for the examples I mentioned at Euxton and Wigston the doubling was done by adding the extra track but leaving the former single lead in place, so the speed for the route that causes most conflict won't have changed.

Yes, that was sort of my point that "single leads are worse than double leads" is only true capability-wise if speeds etc are the same too. At Ely, the Peterborough route was 20mph, with one of the other routes being the "straight" route.

If I recall, at Euxton the space for the double ladder required widening of the A49 Bridge, and at Wigston there is a retaining wall cut into the embankment - both relatively pricey civils works.

 

[MarkyT]

... for the examples I mentioned at Euxton and Wigston the doubling was done by adding the extra track but leaving the former single lead in place, so the speed for the route that causes most conflict won't have changed.

You might plausibly do the same at Ely North, but the siding connection and aggregates facility are very close and would also need a costly remodelling, probably involving a land transfer.

 

[headshot119]

The distance to the point of conflict with the Up Main was much greater than the distance to the Down Relief would've been though, so a collision would be potentially more severe but also much less likely to occur in the first place. On that basis it seems to have been a reasonably sound decision. I guess that it would've made the interlocking arrangements much more complicated too, as the points would be too far apart to work as a co-acting pair without being an operational pain in the posterior.


The Rule Book (S7 1.6) still covers the possibility of a colour light signal that can't display a yellow aspect reading onto another stop signal - I can't think of a single current example, but presumably it was acceptance at some point in history.

Merseyrail on the Wirral Loop is one example of a G/R colour light onto a G/R colour light.

 

[Ianno87]

Merseyrail on the Wirral Loop is one example of a G/R colour light onto a G/R colour light.

I'm intrigued. Is that where (say) you've got an R/G signal Immediately before a platform then an R/G platform starter, which is deemed OK as all trains would normally stop at the platform?

 

[headshot119]

I'm intrigued. Is that where (say) you've got an R/G signal Immediately before a platform then an R/G platform starter, which is deemed OK as all trains would normally stop at the platform?

Not necessarily, while some of the signals have a separate "Repeater" head; which shows Y/G if the signal it sits above is off, or blank if it's on, there are also runs of 2 R/G with no repeaters or platforms.

One example ML536 platform starter at Hamilton Square toward Liverpool, ML534 at Mann Island Junction, ML530, then platform 1 at James Street then ML522 platform starter.

And another ML714 after Birkenhead Central, ML712 on approach to Hamilton Square Junction, ML552 on the approach to Hamilton Square platform 1, then ML536 platform starter.

These are all fitted with tripcocks rather than TPWS.

 

[Ianno87]

Not necessarily, while some of the signals have a separate "Repeater" head; which shows Y/G if the signal it sits above is off, or blank if it's on, there are also runs of 2 R/G with no repeaters or platforms.

One example ML536 platform starter at Hamilton Square toward Liverpool, ML534 at Mann Island Junction, ML530, then platform 1 at James Street then ML522 platform starter.

And another ML714 after Birkenhead Central, ML712 on approach to Hamilton Square Junction, ML552 on the approach to Hamilton Square platform 1, then ML536 platform starter.

These are all fitted with tripcocks rather than TPWS.

I see - thank you.

 

[MarkyT]

Not necessarily, while some of the signals have a separate "Repeater" head; which shows Y/G if the signal it sits above is off, or blank if it's on, there are also runs of 2 R/G with no repeaters or platforms.

One example ML536 platform starter at Hamilton Square toward Liverpool, ML534 at Mann Island Junction, ML530, then platform 1 at James Street then ML522 platform starter.

And another ML714 after Birkenhead Central, ML712 on approach to Hamilton Square Junction, ML552 on the approach to Hamilton Square platform 1, then ML536 platform starter.

These are all fitted with tripcocks rather than TPWS.

London Underground principles! Trains can brake to a stand from sighting distance of the red being approached, and a fully braked overlap is proved clear ahead. Tripcocks fitted long before TPWS dreamed up.

 

[D6130]

The Ansaldo ones in the Cheadle Hulme area work differently - green at the top I think.

Yes, the Italian-manufactured Ansaldo signals between Crewe and Cheadle Hulme show red or yellow in the lower lamp and green or yellow in the upper one.

Merseyrail on the Wirral Loop is one example of a G/R colour light onto a G/R colour light.

When I was doing my class 156 practical handling training back in 1992 between York and Hull, I seem to remember that one of the boxes between Gilberdyke and Hull (possibly Broomfleet or Crabley Creek?) had a two aspect colour light Down Home signal reading onto a semaphore section signal. Normal Absolute Block practice you might say, as far as semaphore signals are concerned but, in my experience, a colour light home signal in an AB area would almost always be three aspect. In this case, it was slightly disconcerting to the inexperienced trainees to have the home pulled off to green and then find the section at red; although, other than in thick fog, the section signal was clearly visible from the home, as you were half-way along the longest stretch of straight track in the country. The Selby-Hull line was one of the best routes in the North of England for route, traction and rules training, as it had every type of double line block system (except for axle counters), every type of level crossing (except for open ones) and just about every different type of signal in the Rule Book.

 

[edwin_m]

When I was doing my class 156 practical handling training back in 1992 between York and Hull, I seem to remember that one of the boxes between Gilberdyke and Hull (possibly Broomfleet or Crabley Creek?) had a two aspect colour light Down Home signal reading onto a semaphore section signal. Normal Absolute Block practice you might say, as far as semaphore signals are concerned but, in my experience, a colour light home signal in an AB area would almost always be three aspect. In this case, it was slightly disconcerting to the inexperienced trainees to have the home pulled off to green and then find the section at red; although, other than in thick fog, the section signal was clearly visible from the home, as you were half-way along the longest stretch of straight track in the country.

According to the Kitchenside and Williams book which was my first grounding in signalling, a three-aspect would always be used in this situation because a driver might be misled on seeing a green on a colour light and forget or miss the faint red light of a semaphore. That was way back in the 70s so that one would have been highly unusual in 1992.

The other reason to provide a three-aspect colour light in that situation would be if there was braking distance from it to the next stop signal (still controlled by the same box). In that case the distant could be cleared even with that semaphore at danger, so if the block wasn't clear a following train could be brought up without having to crawl through station limits from one signal to the next.

 

[Tomnick]

Merseyrail on the Wirral Loop is one example of a G/R colour light onto a G/R colour light.

Ta, forgot about those. It doesn't really fit the context of the Rule Book clause though, which implies a Rule 39-esque form of approach release in lieu of a yellow aspect, whereas Merseyrail is just line of sight onto the red?

 

[MarkyT]

According to the Kitchenside and Williams book which was my first grounding in signalling, a three-aspect would always be used in this situation because a driver might be misled on seeing a green on a colour light and forget or miss the faint red light of a semaphore. That was way back in the 70s so that one would have been highly unusual in 1992.

The other reason to provide a three-aspect colour light in that situation would be if there was braking distance from it to the next stop signal (still controlled by the same box). In that case the distant could be cleared even with that semaphore at danger, so if the block wasn't clear a following train could be brought up without having to crawl through station limits from one signal to the next.

Even where full braking didn't exist between home and next stop signal there were methods available to maaintain a conventional aspect sequence with colour lights, such as delaying the home clearance to yellow automatically with a track timer on approach or having a double yellow on a colour light distant. I wonder if the Hull line installation was a very early colour light, an unusual prewar survivor from before the modern aspect sequence practice was established. LNER were early pioneers of colour lights in the 1920s.

 

[HSTEd]

What we learn from all this is, that whilst interesting, cab signalling cannot come soon enough!

 

[brad465]

Apologies if someone mentioned this and it skipped my eye, but on the approaches to London Victoria, were a row of signals that could show double yellow but not green, which is not unusual for the approach to a terminus, but these ones had the red light in the middle, yellow below and the double yellow bulb above the red, so the double yellow could remain separate but in a rare example of a red light being neither the bottom nor top. However they've all now been converted to LED and while I believe the same colour options are available, the LED capability makes the arrangement more conventional now.

 

[MarkyT]

Apologies if someone mentioned this and it skipped my eye, but on the approaches to London Victoria, were a row of signals that could show double yellow but not green, which is not unusual for the approach to a terminus, but these ones had the red light in the middle, yellow below and the double yellow bulb above the red, so the double yellow could remain separate but in a rare example of a red light being neither the bottom nor top. However they've all now been converted to LED and while I believe the same colour options are available, the LED capability makes the arrangement more conventional now.

There is nothing wrong with that former arrangement as long as the red is closest to the nominal driver's eye level. As others have said, it's important the double interval between the two yellows is provided to avoid confusion with a single yellow. That's a performance issue as clearly a single yellow is MORE restrictive than a double yellow. Red in the middle probably meant contractors could supply slightly cheaper three-lens heads and reconfigure the colour filters to the required arrangement, rather than 4-lens units with one blanked off!

 

[edwin_m]

There is nothing wrong with that former arrangement as long as the red is closest to the nominal driver's eye level. As others have said, it's important the double interval between the two yellows is provided to avoid confusion with a single yellow. That's a performance issue as clearly a single yellow is MORE restrictive than a double yellow. Red in the middle probably meant contractors could supply slightly cheaper three-lens heads and reconfigure the colour filters to the required arrangement, rather than 4-lens units with one blanked off!

I'd say there's a safety issue here too, if the drivers saw something yellow ahead and assumed it was a double yellow and it turned out to be single yellow.

 

[Ianno87]

I'd say there's a safety issue here too, if the drivers saw something yellow ahead and assumed it was a double yellow and it turned out to be single yellow.

There used to be a signal on the (now removed) Down Slow approaching Bolton that could only show a maximum of Double Yellow; but in that case was a 4-aspect head with the green aspect blanked out (I presume was produced with the other 4 aspect heads in the area), so still giving the correct spacing between the Yellows.

 

[d9009alycidon]

While we are on the subject of colour light signals, can anyone explain the history of the hood length on these signals, early MAS installations seem to have had really long hoods, someone told me that this was an ARP measure to prevent the lights being seen from enemy planes, but the long hoods were still being used for installations in the late 1950s long after the threat of "conventional" bombing had receded. Installations form the 1970s have a considerably shorter hood and with the introduction of the LED signal the hood has disappeared altogether.

 

[John Webb]

While we are on the subject of colour light signals, can anyone explain the history of the hood length on these signals, early MAS installations seem to have had really long hoods, someone told me that this was an ARP measure to prevent the lights being seen from enemy planes, but the long hoods were still being used for installations in the late 1950s long after the threat of "conventional" bombing had receded. Installations form the 1970s have a considerably shorter hood and with the introduction of the LED signal the hood has disappeared altogether.

Various photos of colour light signals of installations in the 1920s/30s indicate hood lengths of around a foot. I understand that it was an ARP matter that caused the introduction of 2ft long hoods during WW2. Use of long hoods after the war seems to have occurred on the Liverpool Street - Shenfield resignalling late 1940s, but the York resignalling in the 1950s and the WCML electrification resignalling of the 1960s seems to have been reversions to the shorter hoods. I suspect it may have been a case of using up old stocks of the longer hoods after the war to save costs?

 

[tiptoptaff]

Signals are occasionally mounted horizontally, particularly for mid-platform signals under a canopy, with the red nearest the platform edge. However these can only be three-aspect as double yellow has to be displayed vertically - two yellows horizontally is a "splitting distant" for a junction signal showing danger.

Incorrect on the splitting distant. If the junction signal is at danger, only one head will be lit. Both heads only illuminate when there is a route set through the junction, whether that be diverging or straight ahead.

Closest you'll get to 'horizantal' yellows is if the least restrictive route is showing Double Yellow.

 

[edwin_m]

Incorrect on the splitting distant. If the junction signal is at danger, only one head will be lit. Both heads only illuminate when there is a route set through the junction, whether that be diverging or straight ahead.

Closest you'll get to 'horizantal' yellows is if the least restrictive route is showing Double Yellow.

Noted thanks. I think this may have been true at some time in the past, as I got it from someone or some book at some time, but the standard seems to have changed about eight times and I don't have time to work through the old ones.

 

[tiptoptaff]

Noted thanks. I think this may have been true at some time in the past, as I got it from someone or some book at some time, but the standard seems to have changed about eight times and I don't have time to work through the old ones.

It's only been a short time since they were taught to us in rules. Our trainer was a Reading driver before becoming a trainer so was quite familiar with them.

They stick in my mind because they're so obscure

 

[martin2345uk]

We weren’t even taught them in rules because the instructor didn’t know how they worked.

 

[tiptoptaff]

We weren’t even taught them in rules because the instructor didn’t know how they worked.

That's.... concerning

 

[D6130]

There used to be a signal on the (now removed) Down Slow approaching Bolton that could only show a maximum of Double Yellow; but in that case was a 4-aspect head with the green aspect blanked out (I presume was produced with the other 4 aspect heads in the area), so still giving the correct spacing between the Yellows.

In the days before the invention of double-filament bulbs, some pre-war LMS colour light signals had a second red aspect which automatically illuminated if the main red bulb blew. An example that I recall from my own working days was the Up Section Signal at Settle Junction, which was combined with the distant for the Up Intermediate Block Home signal at Long Preston. This signal had the outward appearance of a four aspect head but was in fact three aspect. The order of aspects, from the top, was green, yellow, emergency red and normal red. It was replaced by a modern three aspect head on a new post in 1997 and the old signal was donated to the Keighley and Worth Valley Railway, who put it on display in the carriage shed museum at Oxenhope - where, incidentally, you can also see an example of the LMS Mirfield area experimental "speed signals" from 1932, which I believe remained in use until the extension of the Healey Mills box area in about 1970.

 

[martin2345uk]

That's.... concerning

Tell me about it.

 

[4F89]

Tell me about it.

I think you had 2 decent weeks.....

 

[martin2345uk]

I think you had 2 decent weeks.....

You knows it.

 

[bengley]

What we learn from all this is, that whilst interesting, cab signalling cannot come soon enough!

And it's a no from me!