Approach release at BL1533

Torfaen · 24 Aug 2026

BL1533 is the third signal westbound from Bristol Parkway, the last one before the junction at Patchway. Line speed is 60 mph, increasing after the junction to 90.

For the past 2 months or so, the signal seems to have been operating with approach control. The route is showing as set on OpenTrainTimes, but the signal is held at red until the train has slowed to 20 or less. There is no TSR signed as far as I can see - and it would anyway seem a bit irregular to slow trains if there was no signage for a restriction.
The only other point of note about this signal is that it's just before an OLE neutral section - not as if that seems in any way relevant.

Does anyone have any ideas what is the reason for the signal operating like this? It's adding at least a minute for everything going westbound, and it's baffling me.

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jfollows · 24 Aug 2026

It may be completely different, but Crewe CE154 operated under a Temporary Approach Control Link for some months, https://www.railforums.co.uk/threads/approach-control-signalling-at-crewe.212702/#post-4926511, pending a fix which took some time to implement.
Similar to your case, all trains had to come to a stand even when the route set wouldn’t normally require it.

66701GBRF · 25 Aug 2026

I don't know what the case is here but sometimes when a part of the signalling system can't be relied upon certain restrictions maybe implemented to either not show a certain signal aspect or reduce the chance of a train passing a signal should it revert to red in front of them.

800002 · 25 Aug 2026

Do you know if the signal concerned steps up to Green from Red, or to an intermediate Yellow / double Yellow depending on number of aspects available on the signal (i don't know the signal concerned).

SWFreight · 25 Aug 2026

Would be interesting to know. When I have experienced this I assumed it was because a train was routed in front from the Up Bristol, or onto the Down Bristol.

Torfaen · 25 Aug 2026

I'm pretty certain it's a 3 aspect. I am sure it steps up to green because the train accelerates up to line speed when it clears, and I know the next signal is not visible until the train gets quite close.

== Doublepost prevention - post automatically merged: 25 Aug 2026 ==

66701GBRF said:
I don't know what the case is here but sometimes when a part of the signalling system can't be relied upon certain restrictions maybe implemented to either not show a certain signal aspect or reduce the chance of a train passing a signal should it revert to red in front of them.

That might be a possible explanation. But, if a part of the signalling system is deemed to be unreliable, e.g. a signal could change to red in front of a train, isn't that something that would normally get urgent attention?

800002 · 25 Aug 2026

Okay, 2nd follow up:

Is it all / most trains you've been or the same train each day that you experience this with?

If so, which service have you been on?

(There are many possibilities, as being described above, but limited data to interrogate).

== Doublepost prevention - post automatically merged: 25 Aug 2026 ==

Torfaen said:
That might be a possible explanation. But, if a part of the signalling system is deemed to be unreliable, e.g. a signal could change to red in front of a train, isn't that something that would normally get urgent attention?

Anything from unreliable track circuit to faulty AWS / TPWS equipment. Although, I wouldn't expect these to endure for very long without being fixed or the route closing.

Im not going to go further, as it won't be helpful.

Torfaen · 25 Aug 2026

800002 said:
Okay, 2nd follow up:

Is it all / most trains you've been or the same train each day that you experience this with?

If so, which service have you been on?

Every train I've taken on that route - since late June, I think. Most often I'm on the 16:37 Cardiff-bound departure from Bristol Parkway, but others I've used have been similarly affected. No idea about freight trains.

Annetts key · Sunday at 18:45

BL1533 protects Patchway junction, so as is common with many junction signals (for busy junctions), the signaller will only set the route when any conflicting moves have cleared the junction. In addition, between this signal and the next signal there is Patchway station. So trains that call at this station will have an impact.

You may say, well if there is a train ahead, why doesn't it clear to a single yellow? I can't tell you why, but the signaller may hold it at red because of other trains going over the junction.

This all depends on the current timetable.

BL1533 is controlled by TVSC at Didcot and is controlled by a computer based interlocking, hence the temporary approach control facility is available from a computer terminal (the technicians terminal) in TVSC at any time. However, modern practice results in this facility being very rarely used. I'm struggling to remember actually seeing temporary approach control being used in the ten years before I left the railway. So I wouldn't expect the temporary approach control to be used unless there is a good reason.

This signal is not provided with normal approach control / approach release, as there is no requirement for it to have this.

The only other special thing about BL1533, is that the next signal is NT1003, which is controlled by the South Wales signalling centre at Cardiff.

In terms of mitigating infrastructure faults, that could also be a reason why the signaller is only routing the signal when a train is actually approaching it. For example, certain problems with points mean only one train will be routed over a crossover (in the normal position) at a time.

PP57601 · Sunday at 22:54

Approach control is a term that is frowned upon by the modern railway.
A Driver should never ‘expect’ a signal to step up on approach, just because it usually does in most circumstances.

PudseyBearHST · Sunday at 23:13

I’ve known signals even out in the sticks with no junction/crossing be approach controlled because of a fault. I think the reason given was that a risk of it reverting back to danger so they/it only cleared on approach. Maybe someone else can offer a better or more detailed explanation of this.

alxndr · Monday at 04:02

Annetts key said:
I'm struggling to remember actually seeing temporary approach control being used in the ten years before I left the railway. So I wouldn't expect the temporary approach control to be used unless there is a good reason.

The only time I can think for seeing it applied was for a banner repeater which was showing blank when off. Temporary approach control allowed us to ensure the front of the train was beyond the banner before clearing.

Annetts key · Monday at 06:56

PudseyBearHST said:
I’ve known signals even out in the sticks with no junction/crossing be approach controlled because of a fault. I think the reason given was that a risk of it reverting back to danger so they/it only cleared on approach. Maybe someone else can offer a better or more detailed explanation of this.

There is a technical difference between the interlocking having temporary approach control / approach release applied and the signaller routing / clearing the signal only when they see a train approaching it (normally via their indications). However from a train drivers perspective these may look similar.

When enabled, temporarily approach control / release will automatically clear the signal from red when the train travels on to the "berth" track circuit (TC) or axle counter (A/C) section for that signal. That is the TC or A/C on approach to the signal. In most cases in a plain line area where there are no points, junctions, manual, CCTV or automatic level crossings that TC or A/C will start after the overlap TC or A/C of the previous signal. So it could be just 200 yards / 183 metres beyond that signal.

In areas where there are points, junctions or level crossings, there will be multiple TCs or A/Cs, so the train may have to get a lot closer to the signal before it travels on to the TC or A/C that operates the temporary approach control / release.

When a signaller clears on approach, normally they wait a while after seeing the indication for the TC or A/C show occupied, so the train will get a lot closer to the signal before the driver sees it clear to a proceed. And the timing will vary between different signallers and how busy each signaller is at the time.

Kentish RYS · Monday at 23:17

PP57601 said:
Approach control is a term that is frowned upon by the modern railway.
A Driver should never ‘expect’ a signal to step up on approach, just because it usually does in most circumstances.

Approach control is not used in the Driving side maybe, but the Signalling side is a different kettle of fish with the various types of approach control/release. A tiny but relevant distinction, as a blanket 'industry doesn't use the term' statement is not quite right

PudseyBearHST · Monday at 23:23

Annetts key said:
There is a technical difference between the interlocking having temporary approach control / approach release applied and the signaller routing / clearing the signal only when they see a train approaching it (normally via their indications). However from a train drivers perspective these may look similar.

When enabled, temporarily approach control / release will automatically clear the signal from red when the train travels on to the "berth" track circuit (TC) or axle counter (A/C) section for that signal. That is the TC or A/C on approach to the signal. In most cases in a plain line area where there are no points, junctions, manual, CCTV or automatic level crossings that TC or A/C will start after the overlap TC or A/C of the previous signal. So it could be just 200 yards / 183 metres beyond that signal.

In areas where there are points, junctions or level crossings, there will be multiple TCs or A/Cs, so the train may have to get a lot closer to the signal before it travels on to the TC or A/C that operates the temporary approach control / release.

When a signaller clears on approach, normally they wait a while after seeing the indication for the TC or A/C show occupied, so the train will get a lot closer to the signal before the driver sees it clear to a proceed. And the timing will vary between different signallers and how busy each signaller is at the time.

Thanks for the detailed explanation! I remember it even being put on the late notices because it went on for a while.

Kentish RYS said:
Approach control is not used in the Driving side maybe, but the Signalling side is a different kettle of fish with the various types of approach control/release. A tiny but relevant distinction, as a blanket 'industry doesn't use the term' statement is not quite right

Of course it’s used on the driving side, a few people/managers may not like it but the majority still use that term. It’s the most basic form of junction control and one that all other forms (i.e. flashing yellows, splitting distants, etc…) will revert to if the conditions aren’t met so to pretend it doesn’t exist is ridiculous and to be very honest quite insulting to my/our intelligence.

LowLevel · Monday at 23:28

PP57601 said:
Approach control is a term that is frowned upon by the modern railway.
A Driver should never ‘expect’ a signal to step up on approach, just because it usually does in most circumstances.

Only by those who think others are incapable of understanding and acting on it appropriately, as opposed to inappropriately by relying upon on it to step up.

It exists and I've always felt a thorough understanding of your working environment is more important than trying to force through an incorrect concept because some people might be incapable of doing their job properly.

If you take the position that following a single yellow you have a red until you see otherwise you'll never go wrong.

On the other hand, if you pretend approach controlled signals don't exist, but keep getting the same circumstances over and over whereby it clears on approach, if you're one of those people prone to forming habits in how they react to that you'll come a cropper on the 1 time out of a thousand it doesn't clear.

PudseyBearHST · Monday at 23:32

LowLevel said:
Only by those who think others are incapable of understanding and acting on it appropriately, as opposed to inappropriately by relying upon on it to step up.

It exists and I've always felt a thorough understanding of your working environment is more important than trying to force through an incorrect concept because some people might be incapable of doing their job properly.

If you take the position that following a single yellow you have a red until you see otherwise you'll never go wrong.

On the other hand, if you pretend approach controlled signals don't exist, but keep getting the same circumstances over and over whereby it clears on approach, if you're one of those people prone to forming habits in how they react to that you'll come a cropper on the 1 time out of a thousand it doesn't clear.

100%. Once you’ve taught approach release to a trainee, you can then have a conversation about the risks. If you decide to pretend it doesn’t exist, you then cannot have this professional discussion about risks and people aren’t stupid, they’ll work it out for themselves like you’ve described.

If certain drivers wish to treat the subject of approach release as “it doesn’t exist” as part of their own personal NTS/risk mitigation strategy, that’s fine but this shouldn’t be imposed on everyone.

Annetts key · 2026-09-01T11:37:55+0100

Just to note that there are other forms of "delayed" aspect changes. One such example, is in a four aspect area where there is insufficient service braking distance between what would normally be a yellow aspect and the next signal that is red. So the signal that would normally show yellow will stay red when routed by the signaller and only clear to a yellow when the interlocking detects a train approaching the signal in rear. Hence the driver of an approaching train will potentially see:
First signal signal showing green.
The next signal showing double yellow.
The next signal showing a single yellow, which steps up to a double yellow as the train approaches it.
The next signal showing single yellow.
The next signal showing red, which may clear to a proceed aspect if and when the signaller has routed it.

There are other examples, such as signals that form double blocking (two consecutive red signals protecting a junction) as well as other variations.

The principle behind the signalling used in this country is that drivers obey the displayed aspect and don't assume or guess what happens next.

Many drivers have been caught out by forming a habit because they do the same move and have the same aspect sequence every day. Until of course there is the one occasion where something different was happening (or not happening as per usual). Then they don't get the aspect sequence they expect but still drive as if they did... Now I don't want to be alarmist, as the vast majority of mistakes don't result in any substantial increase in risk.

This was a such a common problem in the 1970 re-signalling of Bristol Temple Meads that a special monitoring and alarm system was wired in to detect the most common problem (drivers going beyond the special X signals/signs when the gantry signal had not displayed the appropriate aspect for the far end platform and then stopping in the far end {wrong} platform when they were signalled into, and should have stopped in the near end platform).

Modern computer based interlockings and relay based interlockings that have had a monitoring system retrospectively installed can identify many of these driver errors.

I'm not saying this to scare or attack drivers, far from it, 99.99% of drivers are excellent at their job. But am saying this to help understanding of how the signalling system works.

But as the well know expression goes, it's better to be prepared. And that includes knowledge.

I've always been of the opinion that every single driver should have the opportunity to visit a PSB and or a Signalling Centre, or if they mostly drive in a mechanical signalled area, a traditional signal box, so that they can see what signallers do and how the world looks to a signaller. Plus, and this is important, they can see how the signals respond to the signallers controls and, for electrically operated signals, how they respond to the movement of trains.

Ideally, at least some drivers should also be given an opportunity to see a signalling equipment room. To see "the guts" with a signalling technician present, so that they can give an overview (without getting too technical) of what an interlocking actually is.

PudseyBearHST · 2026-09-01T13:38:11+0100

Annetts key said:
Just to note that there are other forms of "delayed" aspect changes. One such example, is in a four aspect area where there is insufficient service braking distance between what would normally be a yellow aspect and the next signal that is red. So the signal that would normally show yellow will stay red when routed by the signaller and only clear to a yellow when the interlocking detects a train approaching the signal in rear. Hence the driver of an approaching train will potentially see:
First signal signal showing green.
The next signal showing double yellow.
The next signal showing a single yellow, which steps up to a double yellow as the train approaches it.
The next signal showing single yellow.
The next signal showing red, which may clear to a proceed aspect if and when the signaller has routed it.

There are other examples, such as signals that form double blocking (two consecutive red signals protecting a junction) as well as other variations.

The principle behind the signalling used in this country is that drivers obey the displayed aspect and don't assume or guess what happens next.

Many drivers have been caught out by forming a habit because they do the same move and have the same aspect sequence every day. Until of course there is the one occasion where something different was happening (or not happening as per usual). Then they don't get the aspect sequence they expect but still drive as if they did... Now I don't want to be alarmist, as the vast majority of mistakes don't result in any substantial increase in risk.

This was a such a common problem in the 1970 re-signalling of Bristol Temple Meads that a special monitoring and alarm system was wired in to detect the most common problem (drivers going beyond the special X signals/signs when the gantry signal had not displayed the appropriate aspect for the far end platform and then stopping in the far end {wrong} platform when they were signalled into, and should have stopped in the near end platform).

Modern computer based interlockings and relay based interlockings that have had a monitoring system retrospectively installed can identify many of these driver errors.

I'm not saying this to scare or attack drivers, far from it, 99.99% of drivers are excellent at their job. But am saying this to help understanding of how the signalling system works.

But as the well know expression goes, it's better to be prepared. And that includes knowledge.

I've always been of the opinion that every single driver should have the opportunity to visit a PSB and or a Signalling Centre, or if they mostly drive in a mechanical signalled area, a traditional signal box, so that they can see what signallers do and how the world looks to a signaller. Plus, and this is important, they can see how the signals respond to the signallers controls and, for electrically operated signals, how they respond to the movement of trains.

Ideally, at least some drivers should also be given an opportunity to see a signalling equipment room. To see "the guts" with a signalling technician present, so that they can give an overview (without getting too technical) of what an interlocking actually is.

Have you got any examples of double yellow -> (potentially) double yellow -> single yellow -> red please? And to clarify the signalling system would not allow double yellow -> single yellow -> red in these locations (even though this obviously wouldn’t be taught to drivers)?

Kentish RYS · 2026-09-01T14:35:16+0100

PudseyBearHST said:
And to clarify the signalling system would not allow double yellow -> single yellow -> red in these locations (even though this obviously wouldn’t be taught to drivers)?

You also get Green -> Yellow-> Yellow -> Red in some places because of under braked signals (I.e. the distance from yellow to red is too short) I know if somewhere this happens due to a 'light' resignalling that didn't move the posts and where switching lines gives this at a junction as the old post locations dont meet the modern standard

*Note edited as I was typing on the train on the way home and made a massive error that made the aspect sequence nonsense *

PudseyBearHST · 2026-09-01T14:50:05+0100

Kentish RYS said:
You also get Red -> Yellow-> Yellow -> Red in some places because of under braked signals (I.e. the distance from yellow to red is too short) I know if somewhere this happens due to a 'light' resignalling that didn't move the posts and where switching lines gives this at a junction as the old post locations dont meet the modern standard

Is it the same for flashing yellows at high risk locations where the junction signal will always step up from single yellow?
I.e.
Flashing yellows -> Steady yellow with JI having to step up to (at least) double yellow -> (at least) Single yellow after junction

If this condition isn’t met (I.e. signal after junction is red and thus junction signal would be single yellow with JI), it would revert to approach control rather than the flashing yellow sequence.

Have I understood correctly?

Kentish RYS · 2026-09-01T15:18:18+0100

PudseyBearHST said:
Is it the same for flashing yellows at high risk locations where the junction signal will always step up from single yellow?
I.e.
Flashing yellows -> Steady yellow with JI having to step up to (at least) double yellow -> (at least) Single yellow after junction

If this condition isn’t met (I.e. signal after junction is red and thus junction signal would be single yellow with JI), it would revert to approach control rather than the flashing yellow sequence.

Have I understood correctly?

Apologies I have edited my post as I made a big error on typing on my phone.

This is details from memory: 3 aspect joins a four aspect line. 2nd 4 aspect signal is red and the single yellow is too close to the red without the double yellow. It is a converging route so the opposite situation to flashing yellows and such.

PudseyBearHST · 2026-09-01T15:31:44+0100

Kentish RYS said:
Apologies I have edited my post as I made a big error on typing on my phone.

This is details from memory: 3 aspect joins a four aspect line. 2nd 4 aspect signal is red and the single yellow is too close to the red without the double yellow. It is a converging route so the opposite situation to flashing yellows and such.

no problem, thanks

Belperpete · 2026-09-01T17:48:12+0100

PudseyBearHST said:
Have you got any examples of double yellow -> (potentially) double yellow -> single yellow -> red please? And to clarify the signalling system would not allow double yellow -> single yellow -> red in these locations (even though this obviously wouldn’t be taught to drivers)?

There certainly used to be cases where there were repeated single yellows in 3 aspect areas, and repeated double yellows in 4 aspect areas. I think that there were even places on the lines into Liverpool Street with three double yellows between green and single yellow. I don't think such repeated aspect sequences are permitted on new schemes, but there may be places where they still exist. The signalling system enforces these aspect sequences where they are required.

I think the preference on new schemes is to apply approach control where there is under braking. This effectively means the driver sees one yellow after another. However, if you look down the line and can see several signals in succession, you won't see an irregular aspect sequence.

== Doublepost prevention - post automatically merged: Yesterday at 18:28 ==

PudseyBearHST said:
Is it the same for flashing yellows at high risk locations where the junction signal will always step up from single yellow?
I.e.
Flashing yellows -> Steady yellow with JI having to step up to (at least) double yellow -> (at least) Single yellow after junction

If this condition isn’t met (I.e. signal after junction is red and thus junction signal would be single yellow with JI), it would revert to approach control rather than the flashing yellow sequence.

Have I understood correctly?

It used to be a requirement that with flashing yellows, the junction signal would be held at single yellow until the train passed the AWS magnet, but this was felt to be too restrictive, and was successively relaxed. I am not sure if the junction signal is held at yellow at all on new schemes, it just shows the appropriate aspect depending on the signal ahead. The theory is that the driver has been warned of the junction by the flashing yellow, and should be regulating his speed accordingly. However, there are likely many places that still have a version of this control.

It also used to be a requirement that the aspect sequence would only step up to flashing yellows if the signal after the junction was off, but that was also relaxed. I don't think it is mandatory on new schemes, only if it is deemed necessary in a particular case. However, there will also be many places that still have this control.

Even in the places that do have this latter control, I don't think that the flashing aspect sequence reverts to approach control if the forward signal is replaced, as doing so could result in the junction signal being replaced to red in view of the approaching train, and then clearing up again when the approach control condition is met.

Junction controls have varied enormously over the years. When I first started, the theory was that you designed the approach control to regulate the speed of trains to the junction speed. However, this became impossible to achieve with the varieties of rolling stock being introduced. Then the theory became that you held the signal at a restrictive aspect (usually but not always red) until the point at which the driver could see the junction or route indicator. However, this was felt to be too restrictive, so various means of advance warning were derived, starting with flashing yellows, but now including splitting distants and preliminary route indicators. Railways with speed signalling don't have the same problems.

PudseyBearHST · 2026-09-01T19:26:35+0100

Belperpete said:
There certainly used to be cases where there were repeated single yellows in 3 aspect areas, and repeated double yellows in 4 aspect areas. I think that there were even places on the lines into Liverpool Street with three double yellows between green and single yellow. I don't think such repeated aspect sequences are permitted on new schemes, but there may be places where they still exist. The signalling system enforces these aspect sequences where they are required.

I think the preference on new schemes is to apply approach control where there is under braking. This effectively means the driver sees one yellow after another. However, if you look down the line and can see several signals in succession, you won't see an irregular aspect sequence.

== Doublepost prevention - post automatically merged: Yesterday at 18:28 ==

It used to be a requirement that with flashing yellows, the junction signal would be held at single yellow until the train passed the AWS magnet, but this was felt to be too restrictive, and was successively relaxed. I am not sure if the junction signal is held at yellow at all on new schemes, it just shows the appropriate aspect depending on the signal ahead. The theory is that the driver has been warned of the junction by the flashing yellow, and should be regulating his speed accordingly. However, there are likely many places that still have a version of this control.

It also used to be a requirement that the aspect sequence would only step up to flashing yellows if the signal after the junction was off, but that was also relaxed. I don't think it is mandatory on new schemes, only if it is deemed necessary in a particular case. However, there will also be many places that still have this control.

Even in the places that do have this latter control, I don't think that the flashing aspect sequence reverts to approach control if the forward signal is replaced, as doing so could result in the junction signal being replaced to red in view of the approaching train, and then clearing up again when the approach control condition is met.

Junction controls have varied enormously over the years. When I first started, the theory was that you designed the approach control to regulate the speed of trains to the junction speed. However, this became impossible to achieve with the varieties of rolling stock being introduced. Then the theory became that you held the signal at a restrictive aspect (usually but not always red) until the point at which the driver could see the junction or route indicator. However, this was felt to be too restrictive, so various means of advance warning were derived, starting with flashing yellows, but now including splitting distants and preliminary route indicators. Railways with speed signalling don't have the same problems.

Thank you

Kentish RYS · 2026-09-01T20:23:40+0100

This is starting to get far away from the thread topic, but I've always thought we could do with more than 4 aspects, such as yellow over green or green over yellow, it just would require a second proved colour, which in relay days was a lot more effort

alxndr · 2026-09-01T21:41:13+0100

Kentish RYS said:
This is starting to get far away from the thread topic, but I've always thought we could do with more than 4 aspects, such as yellow over green or green over yellow, it just would require a second proved colour, which in relay days was a lot more effort

Also potential issues with distinguishing the colours. From a distance or in fog I suspect they’d merge into one unless suitably separated. You’d need to be careful that they would definitely present as the more restrictive aspect if they did.

Approach release at BL1533

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