Signalling for 125mph

[Boysteve]

I have a question. On the ECML (for example) how far apart are the 4-aspect colour light signals so that 125mph running can be allowed?
Also will it be a similar distance on the WCML following the upgrade or can a Class 390 stop from 125mph in the same distance that a Class 87 hauled train could from 110mph?

 

[MarkyT]

I have a question. On the ECML (for example) how far apart are the 4-aspect colour light signals so that 125mph running can be allowed?
Also will it be a similar distance on the WCML following the upgrade or can a Class 390 stop from 125mph in the same distance that a Class 87 hauled train could from 110mph?

One of the big attractions of the IC125 concept in the mid 1970s was that the new trains could stop from 125MPH in the same distance that conventional loco hauled expresses of the time could stop from 100MPH. That meant that, as long as the track and formation could handle it, differential higher speeds for HSTs could be introduced without wholesale resignalling. The same superior braking of Mk3 carriages allowed loco hauled speed to be increased on the WCML with the old signalling when suitable locos became available. Later trains have been specified with braking at least as good as the HSTs so the speed benefits are not lost again.

Here's some data from Railway Group Standard GK/RT0075 which details Signalling Braking Distance and thus minimum signal spacing at a range of speeds for various types of braking performance:

http://www.townend.me/files/brakingdistance.pdf

Note I have only included figures for level track. Rising gradient reduces braking distance, falling gradient increases it. In 3-aspect areas the braking distance for the desired speed will be the minimum spacing between each signal i.e from yellow to red. In 4-aspect, the distance between signals is around half the braking distance. Two sections from the first caution (the double yellow) to the red will be at least the braking distance.
It can be seen that the 'all trains' curve in the graph (blue) becomes a horizontal straight line above 100 MPH, indicating that all trains authorised to exceed 100MPH must have braking performance conforming to the 9% curve (yellow).

The purpose of having the three curves is to allow engineers to reduce signal spacing selectively and apply differential speed restrictions for different traffic types in particularly busy areas, hence to increase capacity where required, otherwise the 'all trains' curve could be applied universally.

 

[LNW-GW Joint]

Nevertheless, much of the WCML was resignalled (and respaced) for 125mph.
Part of it is signal visibility at the higher speed, on a winding route.
Additional signals were also needed between Stafford and Crewe on the recent slow line upgrade from 75mph to 100mph.
Standards have also changed on all the main lines since the last resignalling in the 1960s/70s (eg sighting, overlaps).
The EU TSIs also apply to major upgrades as well as new lines, with ETCS now the standard.

 

[Joseph_Locke]

can a Class 390 stop from 125mph in the same distance that a Class 87 hauled train could from 110mph?

Yes. That is one of the conditions of EPS operation. The signalling works on the WCRM were partly to fix areas where the braking distances were "close" and to fix sighting issues, as 8s at 125mph is 450m rather than 400m at 110mph (and not a few existing locations had less than 8s anyway, at PS ...)

 

[The Planner]

It was only banner repeaters added when the slows between Stafford and Crewe were sped up.

 

[neilb62]

I have a question. On the ECML (for example) how far apart are the 4-aspect colour light signals so that 125mph running can be allowed?
Also will it be a similar distance on the WCML following the upgrade or can a Class 390 stop from 125mph in the same distance that a Class 87 hauled train could from 110mph?

On test 390002 at 200% laden stopped from 144mph in a section + 2 coaches, ie we passed a signal at 144.6, hit the emergency plunger and stopped 2 coaches past the next one! 390's have plenty of brake!

 

[Bald Rick]

Yes. That is one of the conditions of EPS operation. The signalling works on the WCRM were partly to fix areas where the braking distances were "close" and to fix sighting issues, as 8s at 125mph is 450m rather than 400m at 110mph (and not a few existing locations had less than 8s anyway, at PS ...)

When the standard changed from 7 seconds to 8 seconds sighting required, an awful lot of signals became non-compliant.

 

[Supercoss]

On the Midland Mainline where line speed went up to 125mph in places additional banner repeater signals (mainly 3 state ones that can show green) installed and TPWS adjusted on approach to conflict point (junctions mainly) with 'CDR' type conditional double red signalling in use, In English, if a train had a spad at 125mph at signal protecting conflict point it would not stop before conflict point so signal in rear of that signal also kept at danger until speed decrease detected , if train too fast at inner signal TPWS would cause brake demand stopping said train within extra distance clear of conflict point -
so before
G YY Y R junction/conflict point
now
G YY Y R R junction/conflict point (with nothing in block between R - R)

 

[The Planner]

Always a good way to knacker timetables are double reds, adjustment time central.

 

[Tio Terry]

Always a good way to knacker timetables are double reds, adjustment time central.

Knacker timetables or ensure safety?

 

[The Planner]

Both..

 

[moggie]

Always a good way to knacker timetables are double reds, adjustment time central.

Surely it's the red signal (with no route set) protecting the junction that knackers the timetable?

 

[louis97]

In English, if a train had a spad at 125mph at signal protecting conflict point it would not stop before conflict point so signal in rear of that signal also kept at danger until speed decrease detected

The signal in rear (outer signal) will still clear to a proceed aspect on approach whatever the speed of the train. The TPWS grids are placed just before the boundary of the track circuit that releases the signal, which allows the TPWS to check the train speed is below the trigger speed, and then the signal will clear allowing the train to proceed if it is.

 

[The Planner]

Surely it's the red signal (with no route set) protecting the junction that knackers the timetable?

Combination of both, you have added a signal section of slowing down. Normally adds a good minute to a schedule compared to MAR and more again to MAY-FA

 

[JN114]

The signal in rear (outer signal) will still clear to a proceed aspect on approach whatever the speed of the train. The TPWS grids are placed just before the boundary of the track circuit that releases the signal, which allows the TPWS to check the train speed is below the trigger speed, and then the signal will clear allowing the train to proceed if it is.

Just, no.

Firstly, TPWS is a "dumb" system. The only feedback into the signalling control system is aerial failure - in most cases cut into the red lamp proving of the associated signal, but modern VDU signalling systems can indicate TPWS failure independently. It certainly doesn't trigger, or get involved in triggering, approach release of signals.

Secondly, TPWS is set and placed at speeds and distances to stop a train before the conflict point. The issue on the MML Linespeed increase is they didn't move the TPWS grids when they increased the Linespeed. Now the TPWS wasn't capable of stopping a train from full speed before the conflict point, so double-red protection was installed to increase the distance to conflict point. Crude, but cheaper than new TPWS installations.

Finally, approach release on simple TC occupation only really exists for situations where trains are starting from a stand. Ordinarily it's TC occupied for X number of seconds - therefore you have proved a train has been in section longer than it takes to pass through at Linespeed, thus it most be slowing down. Strictly speaking it doesn't prove anything, but it is an accepted assumption in signalling design.

 

[louis97]

Firstly, TPWS is a "dumb" system. The only feedback into the signalling control system is aerial failure - in most cases cut into the red lamp proving of the associated signal, but modern VDU signalling systems can indicate TPWS failure independently. It certainly doesn't trigger, or get involved in triggering, approach release of signals.

Poorly worded post on my part, made it sound like TPWS does stuff it doesn't. I should have said by having the outer signal at red this results in TPWS checking the train speed, as TPWS, in this situation, would only check the train speed if the signal ahead (the outer signal) was at danger.

Secondly, TPWS is set and placed at speeds and distances to stop a train before the conflict point. The issue on the MML Linespeed increase is they didn't move the TPWS grids when they increased the Linespeed. Now the TPWS wasn't capable of stopping a train from full speed before the conflict point, so double-red protection was installed to increase the distance to conflict point. Crude, but cheaper than new TPWS installations.

Crude, but does the job! If only TPWS could be configured to be active at a yellow signal, then you'd have no need for double-reds.

Finally, approach release on simple TC occupation only really exists for situations where trains are starting from a stand. Ordinarily it's TC occupied for X number of seconds - therefore you have proved a train has been in section longer than it takes to pass through at Linespeed, thus it most be slowing down. Strictly speaking it doesn't prove anything, but it is an accepted assumption in signalling design.

I can think of many locations where 'simple' TC occupation is used for releasing approach controlled signals.

 

[Railsigns]

I can think of many locations where 'simple' TC occupation is used for releasing approach controlled signals.

Indeed. The timer isn't there to prove that the train is slowing down; it only proves that the train has reached a point where the junction indicator becomes readable. If the train detection happens to be split in the right place, then a timer isn't always necessary.

 

[JN114]

Poorly worded post on my part, made it sound like TPWS does stuff it doesn't. I should have said by having the outer signal at red this results in TPWS checking the train speed, as TPWS, in this situation, would only check the train speed if the signal ahead (the outer signal) was at danger.

We were at cross purposes then - I hear all kinds of wild claims about how signalling works from people who really haven't a clue - this sounded one of those cases and prejudiced the rest of my reply, apologies.

Crude, but does the job! If only TPWS could be configured to be active at a yellow signal, then you'd have no need for double-reds.

It can! Stage Q of the Reading remodelling introduced some OSS+ grids placed on approach to the signal in rear of the one they "protect" - the energisation tables for them are incredibly complex - and complex usually means £££! It allowed them to increase the line speed on he mains through platforms 9 and 10 and over the flyover from 60 to 95mph.

I can think of many locations where 'simple' TC occupation is used for releasing approach controlled signals.

It may be a regional thing - I've only studied signal design as part of volunteer work I do for a signalling-related preservation society, so have a regional and technological bias towards BR(W) MAS in my knowledge and understanding. In those examples I've studied my initial claim holds true - straight track occupation for approach release appears to be reserved for situations where trains are starting from a stand. If other regions do it differently I'm prepared to submit that the Western did things a little differently!

 

[Railsigns]

Stage Q of the Reading remodelling introduced some OSS+ grids placed on approach to the signal in rear of the one they "protect" - the energisation tables for them are incredibly complex

They may be incredibly complex, for a variety of reasons, however I would suggest that placing the OSS+ loops for one signal in rear of the previous signal has not added to that complexity in any way. The set speed of the OSS+ will be so high that it has no effect on a train braking to stop at the previous signal, so no additional controls are necessary. In other words, it doesn't matter on which side of the previous signal an OSS+ lands.

 

[JN114]

They may be incredibly complex, for a variety of reasons, however I would suggest that placing the OSS+ loops for one signal in rear of the previous signal has not added to that complexity in any way. The set speed of the OSS+ will be so high that it has no effect on a train braking to stop at the previous signal, so no additional controls are necessary. In other words, it doesn't matter on which side of the previous signal an OSS+ lands.

I believe it's more to do with trains taking a diverging route at the intervening signal not being tripped, than interference with trains stopping at the intervening signal.

 

[Railsigns]

I believe it's more to do with trains taking a diverging route at the intervening signal not being tripped, than interference with trains stopping at the intervening signal.

Yes, that would make more sense. And the controls would likely be the same if the OSS+ was in advance of the previous signal but in rear of the divergence.

 

[louis97]

We were at cross purposes then - I hear all kinds of wild claims about how signalling works from people who really haven't a clue - this sounded one of those cases and prejudiced the rest of my reply, apologies.

It can! Stage Q of the Reading remodelling introduced some OSS+ grids placed on approach to the signal in rear of the one they "protect" - the energisation tables for them are incredibly complex - and complex usually means £££! It allowed them to increase the line speed on he mains through platforms 9 and 10 and over the flyover from 60 to 95mph.

It may be a regional thing - I've only studied signal design as part of volunteer work I do for a signalling-related preservation society, so have a regional and technological bias towards BR(W) MAS in my knowledge and understanding. In those examples I've studied my initial claim holds true - straight track occupation for approach release appears to be reserved for situations where trains are starting from a stand. If other regions do it differently I'm prepared to submit that the Western did things a little differently!

No worries, I know exactly what you mean

Ah that's interesting with Reading, learn something new everyday!

 

[MarkyT]

Crude, but does the job! If only TPWS could be configured to be active at a yellow signal, then you'd have no need for double-reds.

A non-overridable enforced slow down from the distant within a given distance or time, like German Indusi, rather than our AWS 'acknowledge and carry on regardless' risk. Thus DB only ever needs one 'OSS' equivalent on final approach to the signal at stop. A limited supervision ETCS L1 system could do that in UK, replacing and enhancing TPWS / AWS functionality without all the complexity of L2.

 

[moggie]

Combination of both, you have added a signal section of slowing down. Normally adds a good minute to a schedule compared to MAR and more again to MAY-FA

Yes, but slowing down for what? I've always been puzzled by the delay cited against junctions with Conditional RR's. Agreed there's an extra signal section to negotiate at caution when the junction signal is red protecting a conflicting move. i.e. the train is likely to have to stop at the junction anyway. However, when the junction signal is at red, set forward and awaiting satisfaction of MAR approach control for the diverging route then there's no restriction of the outer signal - i.e. it would clear unrestricted to yellow. In essence, instead of racing towards a red junction signal the train is slowed down earlier but only when there's no route set through the junction. What aspect sequence is displayed on the approach is of course a moot point when the junction signal is being held at red protecting the junction.

Nevertheless, if a minute goes in the schedule it goes in. Just trying to understand why?

 

[notadriver]

Defensive driving policies ? I don't think schedulers take this into account at all.

Flashing aspects can speed up the approaches to diverging junctions


Sent from my iPhone using Tapatalk

 

[The Planner]

Defensive driving policies ? I don't think schedulers take this into account at all.

We have difficulty doing it yes as TOCs don't tend to share what they are. This is why SRTs that in the past were quite easily achievable are now tight and we are accused of "padding" the timetable.

 

[Joseph_Locke]

Ditton had to have conditional double reds to manage the outcome of a freight SPAD; the "second red" was the only way of "tripping" TPWS sufficiently far in advance of the junction, as a normal OSS and TSS layout would meant that slowish freight would only get caught by the junction signal TSS. The SPAD latches and SPRG arrangements took up more time than anything else ...