AWS and 140mph running

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Mordac

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Okay, so what I'm about to write may be quite silly for those in the know, but it's been bugging me and I want to ask anyway, running the risk of mickey taking. :p

The reason why IC225s and Pendos can't run at 140mph is because it's supposedly dangerous to do so without in-cab signalling. My question is, wouldn't it be relatively cheap and simple to modify AWS to provide this by adding an extra magnet at each instance, so that there were four possible states (2x2) and so information about aspect could be conveyed to the driver (say all magnets off is green, front on and rear off is double yellow, front off and rear on is single yellow, all on is red). Was this ever considered?
 
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Carntyne

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I don't think signalling systems and "relatively cheap and simple to modify" ever go together I'm afraid.
 

sciisfun

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I would have thought it would also include things like speed boards as well, which may be deemed difficult to see at higher speeds (I know HS1's in cab signalling also gives you the line speed) as I would have thought a coloured signal would be easier to see than a speed board (although the argument of route knowledge comers up at this point)
 

Phil.

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Okay, so what I'm about to write may be quite silly for those in the know, but it's been bugging me and I want to ask anyway, running the risk of mickey taking. :p

The reason why IC225s and Pendos can't run at 140mph is because it's supposedly dangerous to do so without in-cab signalling. My question is, wouldn't it be relatively cheap and simple to modify AWS to provide this by adding an extra magnet at each instance, so that there were four possible states (2x2) and so information about aspect could be conveyed to the driver (say all magnets off is green, front on and rear off is double yellow, front off and rear on is single yellow, all on is red). Was this ever considered?

What you're describing/suggesting is a sort of SRAWS(Signal Repeating AWS)that was given trial in the seventies.
The thing with AWS is that it doesn't give an indication of what signal aspect ahead is showing. All AWS can do is differentiate between green - bell and indicator going to black - and caution or danger - horn and indicator showing "sunflower" changing to black upon cancellation of the horn.
As "carntyne" has mentioned in his post cheap signalling system modification is an oxymoron.
 

cjmillsnun

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Okay, so what I'm about to write may be quite silly for those in the know, but it's been bugging me and I want to ask anyway, running the risk of mickey taking. :p

The reason why IC225s and Pendos can't run at 140mph is because it's supposedly dangerous to do so without in-cab signalling. My question is, wouldn't it be relatively cheap and simple to modify AWS to provide this by adding an extra magnet at each instance, so that there were four possible states (2x2) and so information about aspect could be conveyed to the driver (say all magnets off is green, front on and rear off is double yellow, front off and rear on is single yellow, all on is red). Was this ever considered?

Something along those lines was trialed back in the early BR days on the SWML. It worked but was never introduced widely.
 

edwin_m

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Adding extra combinations of magnets would probably confuse the existing AWS equipment, which would need modifying on all trains that might use the route. It would also be difficult to detect combinations of magnets on and off because the "off" ones wouldn't be detectable except perhaps by using a timer whose period would have to take account of train speed. SRAWS used a different technology from magnets, something to do with induction loops I think.

I think the requirement for 140mph running is ATP with full speed supervision, not just cab signalling. AWS wouldn't provide that.
 
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GB

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Okay, so what I'm about to write may be quite silly for those in the know, but it's been bugging me and I want to ask anyway, running the risk of mickey taking. :p

The reason why IC225s and Pendos can't run at 140mph is because it's supposedly dangerous to do so without in-cab signalling. My question is, wouldn't it be relatively cheap and simple to modify AWS to provide this by adding an extra magnet at each instance, so that there were four possible states (2x2) and so information about aspect could be conveyed to the driver (say all magnets off is green, front on and rear off is double yellow, front off and rear on is single yellow, all on is red). Was this ever considered?

If it was that easy and cost effective I'm sure it would have been done to differentiate between single yellow and double yellow which has far more day to day practicalities.
 

ComUtoR

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If it was that easy and cost effective I'm sure it would have been done to differentiate between single yellow and double yellow which has far more day to day practicalities.

I do wonder why the new banners only show 3 states. I would have thought that a yellow banner would be pretty useful too.
 

robbeech

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The flashing green aspect was used on the ECML during testing. Infact there was a thread about this recently, it essentially gave you a 3rd block in which to slow to a stop.

The use of more advanced communication between track and train is necessary here. A speed indication and information about the next signal is required to be sent to the train at frequent intervals (i don't believe it is continuous) as it is deemed unacceptable to expect the driver to see both speed limit and signal aspects when travelling at this speed.
 

dviner

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The use of more advanced communication between track and train is necessary here. A speed indication and information about the next signal is required to be sent to the train at frequent intervals (i don't believe it is continuous) as it is deemed unacceptable to expect the driver to see both speed limit and signal aspects when travelling at this speed.

Does anyone know how much data can be reliably passed between a static balise and a train passing over that balise at speeds of 140MPH+?

Not a rhetorical question - I don't know the answer, but somebody here might.
 

najaB

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Does anyone know how much data can be reliably passed between a static balise and a train passing over that balise at speeds of 140MPH+?

Not a rhetorical question - I don't know the answer, but somebody here might.
According to Wikepedia up to 820 bits - so about 100 bytes by the time parity bits, etc. are included.
 

MarkyT

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Does anyone know how much data can be reliably passed between a static balise and a train passing over that balise at speeds of 140MPH+?

Not a rhetorical question - I don't know the answer, but somebody here might.

I don't know 'how much' data but I understand ETCS balises are designed to be read reliably at the highest speeds on dedicated high speed lines. For a full supervision level 2 system the data would include balise ID, positional information, and perhaps some static data about the route ahead, distance to next balise etc.
 

craigybagel

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Bear in mind the current 125mph without speed supervision or cab signaling is actually pretty high already. In most countries the limit is lower (160kmh on Germany, 79mph in USA for example)
 

Philip Phlopp

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Bear in mind the current 125mph without speed supervision or cab signaling is actually pretty high already. In most countries the limit is lower (160kmh on Germany, 79mph in USA for example)

9mph is too high for the USA, they can barely move a train without it crashing into something, derailing or exploding.
 

whoosh

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The flashing green aspect was used on the ECML during testing. Infact there was a thread about this recently, it essentially gave you a 3rd block in which to slow to a stop.

At the time, all trains that went above 110mph had two drivers in the cab. The AWS would give a bell and black display for flashing green and the same for green. The problem is the bell sound, black display, and green signal, all mean SLOW DOWN - in complete contrast to any other location or situation on the railway, where it means go at line speed.


The initial suggestion of various magnets in a row wouldn't work, as they would cancel each other out - one of the poles is a fixed magnet (always on) and the other is an electromagnet of the opposite pole (on when current is sent through the circuit when the signal is green) which cancels out the fixed magnet. It also means that if the electromagnet fails then the fixed magnet gives a warning.
If you put varying magnets in a row you'd just get what the last one that you went over's indication.
You could use two next to each other side by side, but would need two receivers on the train, they would have to be put at sufficient distance inside the four-foot and through a testing program to prove they didn't interfere with each other, and you couldn't put them outside the four foot as they might then interfere with APS equipment on the train that switches off the Vacuum Circuit Breaker on the train for neutral sections.

It's old out of date technology, and the only way it can cost-effectively be changed, is for it to be done away with and replaced. ERTMS is the replacement.
 
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edwin_m

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At the time, all trains that went above 110mph had two drivers in the cab. The AWS would give a bell and black display for flashing green and the same for green. The problem is the bell sound, black display, and green signal, all mean SLOW DOWN - in complete contrast to any other location or situation on the railway, where it means go at line speed.

I imagine as the 140mph running was only for testing without passengers, they decided the risk was acceptable. Possibly the second driver was tasked specifically with observing the signals?

The initial suggestion of various magnets in a row wouldn't work, as they would cancel each other out - one of the poles is a fixed magnet (always on) and the other is an electromagnet of the opposite pole (on when current is sent through the circuit when the signal is green) which cancels out the fixed magnet. It also means that if the electromagnet fails then the fixed magnet gives a warning.

They are indeed opposite poles but they don't cancel each other out, at least not in the sense of the magnetic fields neutralising each other. Otherwise the system would not be able to detect a green signal and ring the bell. The permanent magnet is detected, the system waits a certain period and if the electromagnet isn't detected by then it sounds the horn (and applies the brakes if not acknowledged within a further period). So it will give a horn instead for a green signal if the apparatus is passed over very slowly, but train stopping positions in platforms are chosen to avoid this.

You may be thinking of the arrangement on some bi-directional lines where suppressing electromagnets are mounted alongside the permanent magnet and energised when a train is signalled in the direction for which the AWS doesn't apply. These genuinely cancel the field so nothing is detected and no indication is given.
 

dviner

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According to Wikepedia up to 820 bits - so about 100 bytes by the time parity bits, etc. are included.

Why didn't I think of looking there?

... and after looking there - why try to re-invent the wheel with magnets?
 
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whoosh

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They are indeed opposite poles but they don't cancel each other out, at least not in the sense of the magnetic fields neutralising each other. Otherwise the system would not be able to detect a green signal and ring the bell. The permanent magnet is detected, the system waits a certain period and if the electromagnet isn't detected by then it sounds the horn (and applies the brakes if not acknowledged within a further period). So it will give a horn instead for a green signal if the apparatus is passed over very slowly, but train stopping positions in platforms are chosen to avoid this.

I did know that - it's what I meant, but that is a much better explanation than mine! :)

As for two drivers in the cab, it was originally brought in above 100mph when HSTs were introduced - a 25% extra gain in speed to 125mph would give a higher workload the driver's union argued. This was later renegotiated to 110mph, and then to single-manning upto 125mph upon privatisation. The point I was trying to make is that now the trains are single-manned there is no back up of another person in the cab, and the 'warning' of the initial slow down from 140mph to 125mph would be a 'clear' green signal with associated 'clear' visual and audible warnings in the cab. Okay double-manned during test runs, but single-manned in service this is unacceptable and not a safe method of working.
 

Nippy

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I do wonder why the new banners only show 3 states. I would have thought that a yellow banner would be pretty useful too.

Surely on a 3 state banner, when the banner is showing (white) off the signal is at yellow/double yellow?
 

Bromley boy

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I do wonder why the new banners only show 3 states. I would have thought that a yellow banner would be pretty useful too.

I suppose if the banner is off and isn't green then the signal has to be showing a yellow aspect - although obviously the banner doesn't distinguish between single and double yellow.
 

edwin_m

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I suppose if the banner is off and isn't green then the signal has to be showing a yellow aspect - although obviously the banner doesn't distinguish between single and double yellow.

I think the suggestion was that a banner could show white for double yellow and yellow for single yellow, or some other arrangement that replicates all four aspects.
 

DerekC

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The point is that full ATP (as in ETCS, BR-ATP etc) supervises the slowing of the train over the whole of the braking curve down to a stand, rather than having a speed trip on approach and train stop at the signal like TPWS. This ensures (almost) that there can't be a SPAD. With TPWS the train can still pass a red signal and infringe the overlap before stopping. TPWS+ is designed to cope with speeds up to 100mph, but as the speed gets higher it gets harder to control the problem of overruns past the signal with "fixed point" systems like TPWS and the probability of a collision gets higher. Hence the prohibition on running at more than 125mph. Modifying AWS would do very little for this problem. Even if the driver had an aspect repeater in the cab (like CAWS in Ireland) it wouldn't trap the "acknowledge and keep going" type of error because AWS can't check whether the train has actually slowed in response to the restrictive aspect.
 
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MarkyT

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The point is that full ATP (as in ETCS, BR-ATP etc) supervises the slowing of the train over the whole of the braking curve down to a stand, rather than having a speed trip on approach and train stop at the signal like TPWS. This ensures (almost) that there can't be a SPAD. With TPWS the train can still pass a red signal and infringe the overlap before stopping. TPWS+ is designed to cope with speeds up to 100mph, but as the speed gets higher it gets harder to control the problem of overruns past the signal with "fixed point" systems like TPWS and the probability of a collision gets higher. Hence the prohibition on running at more than 125mph. Modifying AWS would do very little for this problem. Even if the driver had an aspect repeater in the cab (like CAWS in Ireland) it wouldn't trap the "acknowledge and keep going" type of error because AWS can't check whether the train has actually slowed in response to the restrictive aspect.

Unlike slightly more sophisticated systems such as the German Indusi which on receiving a restrictive signals from the track equipment enforces deceleration within times and distances rather than just requiring acknowledgement or just passing or failing a simple overspeed test.

For instance at the distant . . .

1000-Hz speed limiter[edit]
The 1000 Hz is active along with a yellow signal on a distant signal before a main signal, or on a main signal combined with a distant option for the following main signal, or it is active before a railroad crossing.

The train driver has to acknowledge the cab signaling within 4 seconds (2.5 seconds on trains with an MVB electronic bus) by hitting a button - this is called vigilance control (German "Wachsamkeitskontrolle"). Failing to do so will result in an emergency stop.

After acknowledging the warning signal the train has to stay below the braking curve (German "Bremskurve") - fast trains may travel up to 165 km/h and they must reduce the speed to below 85 km/h after 23 seconds. Note that the operation of high speed trains beyond 165 km/h is not based on visual wayside signals or PZB inductors (using LZB or European Train Control System cab-signalling instead in Germany).

The train cannot be released from the speed restrictions within 700 m after the 1000 Hz activation. After that point the train driver may hit a release button (German "Freitaste"). In later generations the enforced speed limit was extended to 1250 m and the 700 m point is only relevant for the 500 Hz inductor.

By enforcing this behaviour at the distant 1000Hz inductor, when the train arrives subsequently at the 500Hz inductor on approach to a red signal (similar to the overspeed trap in TPWS), its speed has been pre-conditioned such that it will be able to stop within the overlap if already overspeed or the further slowdown behaviour is not complied with, hence DB doesn't require additional overspeed traps for higher speed lines as with UK TPWS+. Furthermore Indusi prevents re-acceleration within set distances of warnings unlike TPWS and AWS so when the final 2000Hz inductor is encountered at the red signal it behaves as a simple trainstop, and again becasuse the previous inductors will have preconditioned the approach speed, a stop within the overlap is guaranteed. Nevertheless Germany uses Indusi only up to a maximum line speed of 165 kph, beyond which other systems that can more accurately determine the deceleration envelopes must be employed.
 

Mordac

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Just to clarify, I wasn't suggesting this should be implemented now, where ETCS is obviously the way to go. I was wondering why it wasn't done back then!
 
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