Questions about UK rail operation

[MarkyT]

Out of interest, are PRIs considered to be “signal aspects” for these purposes? Could you dispense with flashing yellows where PRIs had been installed?

PRIs thus far have only been permitted as supplemental indications and musn't replace the primary method of junction approach signalling, whether a flashing yellow/double yellow sequence or a splitting distant. The idea is to give sufficient preliminary information to avoid misrouting. Without the PRI, speed could still be safely controlled for the divergence but a train might end up on a line it is not supposed to travel on for other reasons such as electrification, class/weight of train, or just to avoid the faff and delay involved in reversing back and rerouting if an otherwise un-doable misroute occurred in a very busy area. The PRI is placed far enough in advance that the driver, if noticing they are being misrouted, has time to stop before the junction signal. For a double flashing yellow approach, there's not usually a problem but for free approaches where there's no appreciable speed difference or where splitting distants are employed, that's not always the case.

 

[Taunton]

AWS was, in its very early times, actually known as cab signalling. It came as a development of the GWR ATC system which was installed by GWR chief engineer Churchward and his S&T colleague from the early 1900s, and the pioneer installations, various branches in Oxfordshire, actually did away with lineside signals at first. It was later realised it was better to keep them as otherwise the locomotive stock was restricted to those so fitted, and the drivers didn't really like it. Churchward listened to his drivers. The GWR pioneered the "sunflower" display, which is a crude form of in-cab signalling, and also on 4-aspect lines the ability to give a different indication at a double yellow compared to a single yellow, done by feeding the ATC ramp with negative current instead of the positive (green)/dead (any caution) which AWS has. It gave a double hoot on the cab ATC. Clever stuff for 1930s technology.

 

[TRAX]

Why wasn’t the double hoot kept ?

 

[Ken H]

AWS was, in its very early times, actually known as cab signalling. It came as a development of the GWR ATC system which was installed by GWR chief engineer Churchward and his S&T colleague from the early 1900s, and the pioneer installations, various branches in Oxfordshire, actually did away with lineside signals at first. It was later realised it was better to keep them as otherwise the locomotive stock was restricted to those so fitted, and the drivers didn't really like it. Churchward listened to his drivers. The GWR pioneered the "sunflower" display, which is a crude form of in-cab signalling, and also on 4-aspect lines the ability to give a different indication at a double yellow compared to a single yellow, done by feeding the ATC ramp with negative current instead of the positive (green)/dead (and caution) which AWS has. It gave a double hoot on the cab ATC. Clever stuff for 1930s technology.

This is right
But AWS also used the electro-magnetic system developed by LNER. They took the best bits of both to make AWS.
It was felt the WR electrical system was not good as it involved a physical connection at speed. AWS there is not physical contact between train and track based equipment.

The OP may also not know that AWS can be placed by speed restriction signs, and also portable gear can be put by temporary speed restriction signs.

No AWS on the London Underground. They traditionally used trainstops. When a signal was at danger, a lever was raised. It would then hit a valve on the train emptying the air brake pipe and stopping the train.

 

[Ken H]

7) When approaching a diverging junction, how much warning do you get to reduce your speed? How do you know when you can speed up again? Are there times when it's entirely down to route knowledge)

replies so far have been about colour light areas. In semaphore areas, a splitting distant is provided.

If the higher arm is raised, the route is set for the main line. If the lower arm is raised the route is set for diverging route to left. If there are more routes then you add more arms. This signal would have an associated AWS magnet. Whether the AWS would give a clear indication for the diverging route depends upon the difference in speed.
Are there any of these left on national Rail?

 

[ComUtoR]

You get stepped banner repeaters too.

 

[Ken H]

You get stepped banner repeaters too.

you do

This tells the driver the stop signal ahead, which is obscured by the footbridge, is clear for the main route.
If the black bands had V's cut out of the ends, then they would be repeating a spitting distant.

 

[MarkyT]

Why wasn’t the double hoot kept ?

The Hudd magnetic system as adapted by BR has two magnets, one a strong permanent magnet, and one an electromagnetic inductor of opposite polarity. The detector unit on the train passes the permanent first and an armature is deflected one way, then shortly after it is reset the other way by the electromagnet if energised, giving the bell indication and requiring no intervention. If the electromagnet is not energised because the signal is not showing green or there is a fault the detector is not reset and the horn/sunflower cab indication is given which must be acknowledged within a few seconds to avoid an automatic brake application. The system as designed can only communicate two bits of information by magnetic means; a locational bit to arm the apparatus and a switchable data bit. BR's Southern Region didn't like standard AWS for various reason and didn't fit the new magnets and train equipment alongside the other regions. There was some work carried out on an alternative SRAWS (Signal Repeating AWS) concept that distinguished between the warning and stop aspects in the cab, but that was significantly more expensive and was abandoned in favour of the standard system which was then widely applied on the Southern from the mid 1970s, although with stronger magnets and a larger air gap, presumably to cope with conductor rail issues. The BR magnetic system was known as ATC during its development before 1959 when the official name was changed to AWS.
A comprehensive reference can be found on the railsigns website: http://www.railsigns.uk/info/aws1/aws1.html

 

[Ken H]

The Hudd magnetic system as adapted by BR has two magnets, one a strong permanent magnet, and one an electromagnetic inductor of opposite polarity. The detector unit on the train passes the permanent first and an armature is deflected one way, then shortly after it is reset the other way by the electromagnet if energised, giving the bell indication and requiring no intervention. If the electromagnet is not energised because the signal is not showing green or there is a fault the detector is not reset and the horn/sunflower cab indication is given which must be acknowledged within a few seconds to avoid an automatic brake application. The system as designed can only communicate two bits of information by magnetic means; a locational bit to arm the apparatus and a switchable data bit. BR's Southern Region didn't like standard AWS for various reason and didn't fit the new magnets and train equipment alongside the other regions. There was some work carried out on an alternative SRAWS (Signal Repeating AWS) concept that distinguished between the proceed aspects in the cab, but that was significantly more expensive and was abandoned in favour of the standard system which was then widely applied on the Southern from the mid 1970s, although with stronger magnets and a larger air gap, presumably to cope with conductor rail issues. The BR magnetic system was known as ATC during its development before 1959 when the official name was changed to AWS.
A comprehensive reference can be found on the railsigns website: http://www.railsigns.uk/info/aws1/aws1.html

Did we export AWS to any other country, or is it just a British thing? Do NI railways use it?

 

[TRAX]

The Hudd magnetic system as adapted by BR has two magnets, one a strong permanent magnet, and one an electromagnetic inductor of opposite polarity. The detector unit on the train passes the permanent first and an armature is deflected one way, then shortly after it is reset the other way by the electromagnet if energised, giving the bell indication and requiring no intervention. If the electromagnet is not energised because the signal is not showing green or there is a fault the detector is not reset and the horn/sunflower cab indication is given which must be acknowledged within a few seconds to avoid an automatic brake application. The system as designed can only communicate two bits of information by magnetic means; a locational bit to arm the apparatus and a switchable data bit. BR's Southern Region didn't like standard AWS for various reason and didn't fit the new magnets and train equipment alongside the other regions. There was some work carried out on an alternative SRAWS (Signal Repeating AWS) concept that distinguished between the warning and stop aspects in the cab, but that was significantly more expensive and was abandoned in favour of the standard system which was then widely applied on the Southern from the mid 1970s, although with stronger magnets and a larger air gap, presumably to cope with conductor rail issues. The BR magnetic system was known as ATC during its development before 1959 when the official name was changed to AWS.
A comprehensive reference can be found on the railsigns website: http://www.railsigns.uk/info/aws1/aws1.html

I see, cheers.

 

[MarkyT]

Did we export AWS to any other country, or is it just a British thing? Do NI railways use it?

NI definitely yes. Wikipedia suggests a couple of Australian applications, one in each of Hong Kong and Taiwan, and a curious enhanced system in Liberia (with no reference). The French system claimed seems nonsense by the date as the Hudd system wan't available until the 1930s.
https://en.wikipedia.org/wiki/Automatic_Warning_System#Liberia
https://en.wikipedia.org/wiki/Automatic_Warning_System#Other_countries

 

[ComUtoR]

Stepped banners
Splitting distants
Approach control
Flashing yellows
Preliminary Route Indicators (PRI)

Any other advanced indications of route ? Nothing is immediately screaming at me. (potentially a green banner but none that I am aware of)

 

[hexagon789]

Ah both are interworked - I knew about the DSD but was wondering if the DVD was a different system. Thanks.

Basically the DSD is the basic system and some trains have a DVD overlaid on it if that makes more sense?

 

[TRAX]

So how does the DSD work when there is no DVD ? If there is no DVD there is no 60-second timer, right ?

 

[ComUtoR]

So how does the DSD work when there is no DVD ? If there is no DVD there is no 60-second timer, right ?

Probably traction dependent. In ours, if there is a fault with the DVD, the train will stick the brakes on. Effectively it would work, you would get the timer, but the brakes would come on because you didn't hear and reset it. If you then isolated it, what would happen is that you will need to keep your feet on the DSD at all times. The second you release it, the brakes will come on. It's like a built in redundancy.

 

[hexagon789]

So how does the DSD work when there is no DVD ? If there is no DVD there is no 60-second timer, right ?

You mean that the stock doesn't have a DVD, as in no timing system overlaid on the DSD?

In that case either the driver must keep the DSD pedal depressed at all times or on some much older stock the power handle held down.

313s and 314s, some 150s have only a DSD pedal, no DVD.

 

[TRAX]

I see. So on the 150 you have to press the DSD pedal all the time while moving ?

 

[hexagon789]

I see. So on the 150 you have to press the DSD pedal all the time while moving ?

I believe so yes.

 

[TRAX]

Okay I understand better now, cheers.

 

[30907]

replies so far have been about colour light areas. In semaphore areas, a splitting distant is provided.

Are there any of these left on national Rail?

Not that I know of. Was Apperley Jn the last?

 

[Taunton]

Why wasn’t the double hoot kept ?

Well the GWR ATC could do three indications when striking the ramp : dead, positive, or negative. AWS doesn't make any physical contact so you can't have the dead phase. As I understand it (you S&T people can correct me) there are two adjacent magnets, the first is permanent, and is North, and the second is an electro-magnet connected to the signal, and can be South. The loco passes over, if the signal is not clear only the North is active, and gives the hoot, if clear it instantly passes over the second South magnet, that activates the bell.

The one I always liked was the Southern Region's 1970s enhancement, Signal Repeating AWS (SRAWS) which they experimentally developed internally in the 1970s. it was installed on the Up line between Bournemouth and Southampton, and in the east cabs of the 4-REP units, which led on that line. It could sound all four signal indications, and an enhancement of the Sunflower showed the driver whichever of the four aspects was last passed, until the next signal. I believe there were three cancellation buttons, one for each cautionary aspect as required. Other rolling stock just showed normal AWS indications. It fell to Not Invented Here politics at BRB HQ. It really was proper cab signals. Did anyone here drive there?

 

[MarkyT]

The one I always liked was the Southern Region's 1970s enhancement, Signal Repeating AWS (SRAWS) which they experimentally developed internally in the 1970s. it was installed on the Up line between Bournemouth and Southampton, and in the east cabs of the 4-REP units, which led on that line. It could sound all four signal indications, and an enhancement of the Sunflower showed the driver whichever of the four aspects was last passed, until the next signal. I believe there were three cancellation buttons, one for each cautionary aspect as required. Other rolling stock just showed normal AWS indications. It fell to Not Invented Here politics at BRB HQ. It really was proper cab signals. Did anyone here drive there?

There's a description of the system and an illustration of the cab equipment on this page (search SRAWS):
http://www.wbsframe.mste.co.uk/public/Surbiton_Panel.html

Southern Region/Signal Repeating AWS (SRAWS)
Originally called "Southern Region AWS", its name was later changed to "Signal Repeating AWS". The SRAWS system repeated the next signal's aspect (and displayed a reminder of the previous signal's aspect) on an indication inside the cab. Any aspect other than green had to be acknowledged by the driver pressing the correct button that corresponded to the indication on display. If the driver did not acknowledge the indication, or the wrong button was pressed, an automatic brake application was initiated. The risk of error from subconscious cancellation was therefore greatly diminished.

Above: SR AWS Cab setup. Development of SR-AWS, with signal past indications on left and signal approach indications on right. Note the km/h only calibrated speedometer.

During 1971 an experimental form of cab signalling (SRAWS - Signal Repeating AWS) which was being trialled in the up-direction between Byfleet [it may have been Woking] and Raynes Park (as well as in the New Forest area). The cab layout showed the driver the aspect of the next signal and the one that the train had just passed. Its used a coax aerial loop figure of eight in the track with a frequency module in the signal location to pass a radio frequency code to the train depending on the signal aspect. Development of SRAWS ended in 1975 when the British Railways Board dictated that the Southern Region should equip its lines with standard BR AWS.

The system was apparently much more expensive than BR-AWS which was it's downfall. I can see that trackside interface wiring would be significantly more involved than for AWS, but the coax track loop aerial between the rails might have been cheaper and easier to install than heavy AWS magnets, although might also be more vulnerable to damage.

 

[hexagon789]

The one I always liked was the Southern Region's 1970s enhancement, Signal Repeating AWS (SRAWS) which they experimentally developed internally in the 1970s. it was installed on the Up line between Bournemouth and Southampton, and in the east cabs of the 4-REP units, which led on that line. It could sound all four signal indications, and an enhancement of the Sunflower showed the driver whichever of the four aspects was last passed, until the next signal. I believe there were three cancellation buttons, one for each cautionary aspect as required.

SRAWS sounds very like the Continous Automatic Warning System (CAWS), used in the Republic of Ireland since about 1983/4. It shows the signal aspect on a display and the updates to the next signal on approach. A change to a more restrictive aspect is accompanied by a tone and must be acknowledged by button or a brake application is made. Just one acknowledge button AFAIK though but SRAWS sounds vet similar in principle if not technically.

 

[MarkyT]

SRAWS sounds very like the Continous Automatic Warning System (CAWS), used in the Republic of Ireland since about 1983/4. It shows the signal aspect on a display and the updates to the next signal on approach. A change to a more restrictive aspect is accompanied by a tone and must be acknowledged by button or a brake application is made. Just one acknowledge button AFAIK though but SRAWS sounds vet similar in principle if not technically.

It does doesn't it. The Irish technology came from the US originally, and superimposes varying pulse code frequencies on the basic 50Hz or 83.3Hz track circuit carrier signal, which are detected and interpreted on board. On most of the mainline network the codes are used to update cab repeats of previous and upcoming signal aspects with a warn and acknowledge on step down function as you describe, but on the DART units a more sophisticated ATP also uses the codes for enforcing speed restrictions associated with each aspect.

 

[hexagon789]

It does doesn't it. The Irish technology came from the US originally, and superimposes varying pulse code frequencies on the basic 50Hz or 83.3Hz track circuit carrier signal, which are detected and interpreted on board. On most of the mainline network the codes are used to update cab repeats of previous and upcoming signal aspects with a warn and acknowledge on step down function as you describe, but on the DART units a more sophisticated ATP also uses the codes for enforcing speed restrictions associated with each aspect.

I wonder if CAWS would've been cheaper for BR to fit.

 

[MarkyT]

I wonder if CAWS would've been cheaper for BR to fit.

I'd say definitely more expensive. SRAWS would have been cheaper than CAWS, and BR might have sold it to IE in the 70s. CAWS has the advantages of earlier better aspect update although perhaps SRAWS might have had that option added with more extensive track aerials, at extra cost of course. There's a quantity of expensive specialist equipment required to generate and switch the range of codes in CAWS, and it needs TCs to superimpose the control codes on whereas in UK AWS was provided widely at distant signals at the outer extremities of older AB signalbox control areas, where track circuits rarely existed.

If I was going to design a simple modern UK AWS/TPWS update, I'd go for similar limited supervision (LS) functionality using digital Eurobalises to replace the legacy trackside transponders, like the Swiss National Railways SBB did, completing the modernisation of their entire standard gauge network in 2017. By persuading the ETCS committees to incorporate the Level 1 LS mode into the standard specs they also simultaneously achieved nationwide European interoperability, despite not even being in the EU!

 

[Taunton]

The Irish technology came from the US originally, and superimposes varying pulse code frequencies on the basic 50Hz or 83.3Hz track circuit carrier signal, which are detected and interpreted on board. On most of the mainline network the codes are used to update cab repeats of previous and upcoming signal aspects with a warn and acknowledge on step down function as you describe, but on the DART units a more sophisticated ATP also uses the codes for enforcing speed restrictions associated with each aspect.

The US system it is based on is, I believe, the one devised by Union Switch & Signal Corp (US&S), who devised various clever signalling systems very early on which have stood the test of time, such as CTC. The cab signals product, which is what this is, came along in the 1920s (yes!!), and was instrumental in the US legislation that any passenger train exceeding 79mph must be fitted with cab signals. it was even quite widely installed on the last high speed steam locomotives. The Chicago & North Western, on their main Chicago-Omaha line (now Union Pacific) was one of those who removed lineside signals on this busy double track route when they installed it, which among other things means that any train from another company which gets diverted over this line has to have a UP pilot loco on the front. Being a manufacturers' product, it got sold to many different railroads, so Amtrak diesels, which cross the country on different company routes, can use it wherever they are permitted to run at high speed.

Here's a good description. Who else knew that cab signals are widely installed across Russian railways?

https://en.wikipedia.org/wiki/Pulse_code_cab_signaling

 

[4069]

Not that I know of. Was Apperley Jn the last?

No, Larbert- but they have all gone now.

 

[hexagon789]

I'd say definitely more expensive. SRAWS would have been cheaper than CAWS, and BR might have sold it to IE in the 70s. CAWS has the advantages of earlier better aspect update although perhaps SRAWS might have had that option added with more extensive track aerials, at extra cost of course. There's a quantity of expensive specialist equipment required to generate and switch the range of codes in CAWS, and it needs TCs to superimpose the control codes on whereas in UK AWS was provided widely at distant signals at the outer extremities of older AB signalbox control areas, where track circuits rarely existed.

If I was going to design a simple modern UK AWS/TPWS update, I'd go for similar limited supervision (LS) functionality using digital Eurobalises to replace the legacy trackside transponders, like the Swiss National Railways SBB did, completing the modernisation of their entire standard gauge network in 2017. By persuading the ETCS committees to incorporate the Level 1 LS mode into the standard specs they also simultaneously achieved nationwide European interoperability, despite not even being in the EU!

I'd have thought IÉ would've give for the cheaper option, seems an awful lot of trouble to import a signalling system from abroad.

The US system it is based on is, I believe, the one devised by Union Switch & Signal Corp (US&S), who devised various clever signalling systems very early on which have stood the test of time, such as CTC. The cab signals product, which is what this is, came along in the 1920s (yes!!), and was instrumental in the US legislation that any passenger train exceeding 79mph must be fitted with cab signals. it was even quite widely installed on the last high speed steam locomotives.

From what I understand the Interstate Commerce Commission passed an Order in 1927 requiring railroads to install either an automatic trainstop or cab signalling system on at least one line for trial purposes. The 79mph rule came in with a 1947 order though it was well into the '50s before it took full effect on all railroads.

 

[DanDaDriver]

In that case either the driver must keep the DSD pedal depressed at all times or on some much older stock the power handle held down.

313s and 314s, some 150s have only a DSD pedal, no DVD.

156’s don’t have vigilance. Or the ones I drove didn’t.