Approach release at BL1533

[Torfaen]

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.

 

[jfollows]

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]

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]

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]

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]

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: Tuesday at 08:05 ==

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]

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: Tuesday at 08:11 ==

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]

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]

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]

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]

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]

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]

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.