AWS and LUL lines

Thanks for the reply tut. The only reason why I was asking is I'm running the Bachmann s stock train on my model layout which has AWS ramps in installed and I did not know if AWS ramps was installed in the real world on LUL/network rail lines. Thanks for the answer

They're not installed anywhere the S8s go, but there are a few places where the S7s go that have AWS, like I say. The S stock can't make any use of AWS though, it doesn't receive anything from the magnets or display any kind of AWS indications.

ah, so thats because the routes are signalled by LUL?

so what happened in the old days before privatisation? and even older?  The days when any train could go almost anywhere, and even an HST is said to have used the joint line, running to Marylebone via Rickmansworth and Harrow?

Simon

So for a modelling point of view do I need to place tripcock ramps on the side of the rail opposite the signals then if it's got AWS ramps installed?

On the Wimbledon and Richmond branches AWS ramps are fitted in the rear of signals (usually beyond the platforms at stations) and TPWS loops at the signal itself.

"In the rear of . . " = before
"in advance of . . " = after

Is it just the TSS (Train Stop System) that's fitted, or is the OSS (Over Speed System) fitted too?

For those who don't know, the TSS is the single loop at the signal that does the job of a train stop and stops a train in the event of a SPAD.

The OSS consists of one or more pairs of loops on the approach that ensure that a train does not approach a signal too fast to stop. It can also be used to enforce PSRs (Permanent Speed Restrictions) and is perhaps closest to speed control signalling on LU.

More info.

Firstly as regards AWS

(1) IT IS NOT FAIL-SAFE, a driver may cancel a 'caution' alert within the perscribed 2 seconds and continue. This is what happened at Purley in 1989 and is why it cannot be compared to L.U. tripcocks
(2) It was originality developed as an aid for STEAM LOCOMOTIVE drivers to give them advance warning of the sate of SEMAPHORE DISTANT SIGNALS (see the Harrow & Wealdstone crash of 1952)
(3) It is usually installed 200 yards (183m) before (i.e. on the approach to) the signal to which it applies.
(4) Where fitted to colour light signals, the signal MUST be able to show a cautionary (i.e. yellow) aspect - AWS is not usually fitted to signals only capable of showing red or green
(5) Since the mid 70s (and several nasty crashes) it has been used to alert drivers to significant Permanent Speed Restrictions.
(6) Away from lines fitted with 4 rail electrification (i.e. lines used by L.U. it has also been used to give drivers warning of Temporary Speed restrictions
(7) It is MANDATORY (and has been for several decades) for all UK mainline traction to have it fitted. Following the Ladbroke Grove disaster it is also a requirement that it MUST be working on ALL passenger trains - if it fails mid journey passengers must be de-trained at the earliest opportunity or a pilot loco with working AWS must be attached.

Secondly as regards TPWS

(1) It is fail-safe in the sense that a driver cannot intervene if the system is activated - they are bought to a stand and must wait 2 minutes before they can move again. Furthermore isolating it can only be done when at a stand.
(2) Generally TPWS is only fitted to signals where the consequences of a SPAD could be significant - basically this means signals protecting pointwork and level crossings. Automatic signals are generally not fitted with TPWS.
(3) Most signals fitted with TPWS will require one or two Overspeed loops on the approch (depending on linespeed) to signal fitted with TPWS
(4) Standalone Overspeed installations can also be used for Permanent speed restrictions.
(5) It is MANDATORY for all powered stock to be fitted with TPWS except where alternative protection (e.g. Trainstops on L.U. or the Tyne & Wear system)
(6) It is MANDATORY for the TPWS system to be working correctly - of it becomes defective while the train is in service the same rules apply as with AWS.

Generally yes, however there were reports of new TPWS installations at signals where the track had been previously lifted! Apparently one gang were unable to install a TPWS loop until someone with a chainsaw had cut down the tree growing in the four-foot at the intended location of the loop.

On the whole this is a good summary, but I think you may have been misled slightly (unless it's my own source that is off the mark).

The Train Stop System does use two loops, but the "trigger delay timer" does not operate when a TSS arming loop frequency is detected. The system works by requiring a TSS arming loop frequency to be detected and then a trigger loop frequency to be detected whilst the arming loop frequency is still being detected. This is why they are right next to each other, so that the frequencies can be detected together. The reason for this - why we have two loops - is because the arming loop frequency has to be detected first, then the trigger loop frequency. Which means the TPWS does not have to be suppressed for moves in a direction to which it does not apply. In the other direction, the trigger loop frequency will be detected first, then the arming loop frequency will be detected while the trigger loop frequency is still being detected. But it won't stop the train, because the trigger loop frequency was detected first. So the train gets stopped if the arming and trigger loop frequencies are detected together and the arming loop frequency was detected first. That's why there are two loops and that's why they're right next to each other. Obviously, if you didn't have two loops, you'd have to have some kind of suppression for moves in the other direction. Obviously, you want them next to each other, so that the brakes always come on immediately on passing the TSS - whatever speed you're doing

I heard an HST ran down the Watford DC line to Euston once.

The Bletchley to Aylesbury line has been closed for quite a few years between Bletchley and near Claydon. The track at Swanbourne has been stolen! Therefore this move must have taken place many years ago. Is love to see any photos.

An interesting discussion so far on signalling protection.

NOTHING is the answer - I am aware of at least one trainstop installation where the arming and trigger loops got reversed during a track renewal resulting every train coming into a reversible platform being tripped, while there was no protection to trains leaving the platform.

As you say, unlike AWS, TPWS itself is not fail - safe because the loops must be powered to stop the train. However this non-fail safe nature of the equipment is mitigated by a high level of error checking and fault reporting within the TPWS system, combined with fail-safe modifications to the signal control circuitry.

An HST is rumoured to have reached Marlylebone, but I have never seen a photo. Part of the Claydon - Bletchley track HAS been stolen (is probably in China by now), but the Aylesbury - Claydon - Bletchley section was only used regularly to service Marylebone's Class 115s at Bletchley, and was used for advertised "Santa Specials" from Ruislip, Denham, Gerrards Cross etc, to Milton Keynes for all of the three weeks before Christmas in the late 1980s. I still have a promotional circular for one of these somewhere and it was also advertised as calling at one of the intermediate stations, I think it was Winslow. One of the locals, mysteriously produced the original station sign for each occasion.

The HST rumour began soon after a major emergency occurred on the Euston Line at the London end, and it is alleged that the driver had route knowledge (OR picked up a pilot at Bletchley), enabling a train that had already left Birmingham to divert at Bletchley and get the pax to London. I think, but have no proof that the last Santa Special ran in about 1991. The HST rumour was at around the same time.

Although it might initially be of surprise that I have seen no photo of this HST on the Marylebone route, it must be remembered that mobile phones did not have the technology within them 25+ years ago for this "evidence" to be obtained as I am sure it would be today. (But it couldn't - as the track at Swanbourn etc..........)

Here are a couple of nice links:

One, two.

The TSS loops aren't powered up if the signal is displaying a proceed aspect (anything other than 'danger'), but if you've got a reversible line, then you're gonna have red signals applying to the direction the train isn't travelling in. So if you've got an up train running along the line, all of the down direction signals will be at danger. So that'd mean having a means to detect the direction of travel of any approaching train and suppressing the vital TSS system that must not fail to trip any trains it needs to trip.

Instead, you have an arming loop and a trigger loop. These loops transmit different frequencies. You also have two different sets of frequencies - A and B - one for moves in one direction and one for moves in another.

So, frequency set A. The arming frequency f3 is 66.25 kHz and the trigger frequency f2 is 65.25 kHz. Let's say this set is used for up direction moves.

Frequency set B. The arming frequency f6 is 66.75 kHz and the trigger frequency f5 is 65.75 kHz. Let's say this set is used for down direction moves.

So, the way it works is, if a train detects f3 and then detects f2 while f3 is still being detected, the train stops. An up direction train passing an up direction signal at danger will receive this.

If a train detects f2 and then detects f3, even if f2 is still being detected, nothing happens. A down direction train passing over the TPWS loops for an up direction signal at danger will receive this.

If a train detects f6 and then detects f5 while f6 is still being detected, the train stops. A down direction train passing a down direction signal at danger will receive this.

If a train detects f5 and then detects f6, even if f5 is still being detected, nothing happens. An up direction train passing over the TPWS loops for a down direction signal at danger will receive this.

Either set can be used for either direction, it doesn't matter, it only matters that if you have any kind of nesting or interleaving, you use one set of frequencies for loops applying to one direction, and the other set for the other direction.

If you had only one loop, you'd have to have a method of suppressing the loop, which is not good. We have two loops and the requirement that the frequencies be detected in the correct order to mean that the loops can be powered up if a signal is at danger and will not trip trains travelling in the other direction.

If you had only one set of frequencies then you'd have to be very careful where you placed your loops. It's notable that the OSS trigger frequency is the same as the TSS trigger frequency.

The TSS uses different frequencies to the OSS and the "trigger delay timer" is not involved. This means that an intervention always occurs if a train passes an energised TSS, unless the train stop override functionality has been used for the purposes of passing a signal at danger under rule. This is the other advantage of two different systems - the TSS can be overridden. The OSS cannot be overridden. The train stop override may only be operated when the train is stationary.

With OSS loops it's a similar principle, you have two sets of frequencies A and B.

So, frequency set A. The arming frequency f1 is 64.25 kHz and the trigger frequency f2 is 65.25 kHz. Let's say this set is used for up direction moves.

Frequency set B. The arming frequency f4 is 64.75 kHz and the trigger frequency f5 is 65.75 kHz. Let's say this set is used for down direction moves.

So, the way it works is, if a train detects f1, the trigger delay timer is activated. This timer lasts for 974 ms for passenger trains (1218 ms for freight trains). If the train then detects f2 before the delay time has expired, the train stops. An up direction train approaching an up direction signal at danger too fast will receive this. An up direction train will also receive this if it approaches an up direction PSR too fast. Obviously, the system works by placing the loops a suitable distance apart so that a train travelling at speed x or greater will reach the trigger loop before the time is up and a train travelling at less than speed x will not.

If a train detects f2, without having detected f3 or f1, nothing happens. A down direction train passing over the OSS loops for the up direction will receive this.

Now then, if a train detects f4, the trigger delay timer is activated. If the train then detects f5 before the delay time has expired, the train stops. A down direction train approaching a down direction signal at danger too fast will receive this. A down direction train will also receive this if it approaches a down direction PSR too fast.

If a train detects f5, without having detected f6 or f4, nothing happens. An up direction train passing over the OSS loops for the up direction will receive this.

Makey any sensey?

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Or more succinctly, quoting from AWS and TPWS Interface Requirements: