Route signalling as apposed to speed signalling.

I think the link from mrfs42 should be to www.signalbox.org/, with its forum at www.signalbox.org/forum/index.php .

A point I would make is that most (or at least many) 'speed' signalling systems are actually 'speed differentiated route' (as distinct from geographic or geometric differentiation).

While some speed signalling applications do use three tri-colour lights, this is by no means universal. I would say that overall speed signals don't end up intrinsically 'larger' or more complex (although being unfamiliar with them they may appear so) than route signals - especially in complex areas.

I think a lot depends on what you want to tell the driver - to what extent should he know/be responsible for where he's going (or is it all down to the signalman?), and to what extent should he know or be told about e.g. speed limits.

And to what extent can a change in 'principles' be made... semaphore signalling (in Britain) was always route oriented, colour light route signalling (as we have it now) has just continued from that. I'm not sure to what extent it's true to say that we 'chose' route signalling, I suspect a more accurate statement would be that we just carried on developing route signalling, rather than choosing to change over to speed signalling.

Whilst the Mirfield scheme was a purely British speed signaling system, the New Line scheme was purely a route signaling scheme. The signaling gave no other indication other than the state of the line at the signal and up to the next signal. The Yellow over Red mentioned in the original instructions dated 17th Apr 1932 was a result of the fact that as installed the red marker light only extinguished when the green main aspect was displayed. The signaling was altered with the instructions from 31st August 1936 to display the red marker light only when the red main aspect was displayed. The use of two yellows was limited and only applied as does double yellows as now when on approach to certain junction signals and working as a splitting distant.

We-ee-ll that isn't quite so strange when you contrast it against passing a gantry of signals with one out of a few arms at green and the rest at red. Look at the 'Rugby Bedstead' for a start: if you had one arm and it's associated distant off that would be two greens (plus two greens on the co-actors) with 20 + 20 reds to spot at night and in thick fog... All on the same signal gantry and all glimmering like glowworms. No intensified lights or yellow distants. Routes - don'cha mean roots?



Absolutely! Actually, given the block system in question (if it's the one I taught you) it definitely isn't Absolute but still works in an absolute fashion.

Actually... That reminds me; and I'd have to dig through the oter reaches of my notes to check..... I'm pretty sure that at the period in question when Britain was dithering over speed or route signalling there were no major installations of speed permissive signalling.

Bearing in mind that when these discussion were taking place there was still a large amount of lines worked on permissive block - not just permissive platform working either! To instigate such a sea-change in operating practices between route and speed and then you throw permissive working in the mix then you can easily understand why Britain elected to remain a route signalled nation.

See I told you, this wasn't an easy question to answer!

However, that isn't to say that there hasn't been successful mixing of three-position speed signalling and two-position route signalling. Looking back through my collection of Victorian Railways signalling paperwork there was a distinct era of transition where (especially in the Melbourne suburban district) where drivers were expected to be able to seamlessly transfer between speed and route signalling and back again. I don't know how successful this protracted period of transience was: at a rough guess I would suggest that it went on between the late 30s - 50s. I'm honestly not sure. <note to self> must also look at WAGR and NSWGR practice</note to self>

To reiterate, if I were a British signalling engineer of the period examining what benefits could be gained through the introduction of speed signalling I would want various questions answering:

• how much additional burden would be placed on the rules and regulations department in introducing new practices?
  
• if I wanted long stretches of automatics, what benefit would be gained from speed signalling compared to (say) the low-pressure EP semaphore automatics of the LSWR?
  
• would I save any cores (this, I suspect would be a very emphatic 'NO')?
  
• Power supplies? Could I run this all off accumulators, as the majority of locations are remote from a mains supply[1].
  
• How many Leclanché cells are needed to power three continuously-lit signals?
  
• Can I make the speed signals approach-lit to conserve battery power?
  

I hope you get my drift - this isn't an easy question to answer. ;D


[1] Yes, I do realise the anomaly of a battery lit motor-worked mechanical colourlight.

Hmm. It would be only be three lots of three heads (with two dwarfs underneath) if it were signalled by speed.

[EDIT: this is route signalling at its flagrant zenith!: Rugby Bedstead]

Aha! This is one of your cunning traps, isn't it? ;D [1]



True - if you remember the original context of that quote look at this and you will see I have made amends for that squiggle!

[1] if it isn't then you've made a very lucky guess in making me say that in certain complex junction type circumstances speed signalling results in less infrastructure!

After a bit of digging around to find near-equivalents for people to compare route and speed signalling here are Plaistowand St Albans. St Albans is on the Sydenham line, and has the added interest of being a mechanical box with speed signalling.

I'm glad you found the key - it would have taken me ages to find my paper copy!

Of relevance to UndergrounD signalling - note the use of 'stick' referring to types of signal.

A couple of other comments on the St Albans diagram (based on hunting through the VicSig site, etc.):
1) The No. 1 Rd platform used to be the other side of the Main Road Crossing/Signal SAB9 (see www.vrhistory.com/Locations/St%20Albans.pdf for the development of the station and its signals).
2) The bottom lights on signals SAB9, 20, 21 & 35 are there to provide shunt signal indications (and sigs 25 & 30 are purely shunt signals - my understanding is that 30 can permit a move into any of the three platforms)
3) One of the features of Victorian three position/speed signals (from the start) was that there was always at least a second light as a marker - a number of the signal lights are only there because of this, or to act as place holders (when effectively they replace a speed limit board).
4) Signal M602 (& M622) appear to protect something off the diagram - they replaced an earlier, simpler one (which was just like M655)

Not at all - although I can see (with the benefit of having circuit diagrams in front of me) why you might think I was considering the change from semaphore to colour light. I composed those questions expressly along the line of changing from route based semaphore to speed based semaphore - granted I was considering electrically lit semaphores.



Yes, but the scheme would fall foul of the third question; unfortunately. I can envisage a horrible tangle of return indication locking, locks and economisers - even for what is ostensibly a purely mechanical installation.



I'm not so sure, to be honest. Have you read the March 1937 SA for the Central Division that covers the Mirfield installation? To my mind it seems exceptionally prescriptive, even for local instructions; however, this is a personal opinion and therefore quite subjective. The New Lines instructions esp. 'Additional Instructions respecting the Multiple Aspect Automatic and Semi-Automatic Colour Light signalling on the Electrified Lines between Camden No 2 and Watford Junction No 4 Signalboxes' written 5 years previously seem much more generic and applicable network-wide. The wording in the 1937 SA seems to be a retrograde step compared to the New Lines.