[Technical Question] OSS + PoSA

[ComUtoR]

Afternoon all,

On approach to some signals there is an OSS TPWS when the signal is red. Too fast and trip...

With a PoSA the TS TPWS is obviously not 'active' and you don't need to isolate the TPWS. However, is the OSS on approach still active ? Can it be tripped ? The signal is now considered 'clear' so there is no need to stop the train as the intention is that the signal will be passed.

I'm aware that with the PoSA it feels like the signal is Approach Controlled ? as you are almost brought to a stand before it flashes and you can hold back and it steps up with the PoSA.

Cheers in advance and technical corrections always welcomed

Com.

 

[carriageline]

Good evening sir!

You are correct. The TPWS treats the POSA as a proceed aspect, thus the TSS is disarmed, and you can go on your merry way.

So:
1)Signaller sets POSA route
2) The signal remains at red
3) Once train occupies approach track circuit (last track circuit immediately on approach to signal), the interlocking will wait a preset amount of time to ensure the train has been bought “to a stand, or nearly at a stand”. (How that time is worked out I don’t know, maybe it’s from trackcircuit length?)
4) POSA flashes, TSS disarms

Regarding the OSS, it’s a good question. I would of thought there was no OSS sensors within any approach track circuits, as the area you are talking about is densely signalled. If that is the case, you shouldn’t be able to go over any OSS grids with the POSA off, as your not yet close enough.

But, being the railway, and you’ve obviously asked for a reason, there will be an exception! And the core is low line speed..

This is quoted from the POSA standard

Where the Train Protection and Warning System (TPWS) is provided at a signal, the TPWS train stop sensor (TSS) and any associated TPWS overspeed sensor (OSS) shall be de-energised when the PoSA aspect is displayed.

So I guess that answers your question!

 

[westcoaster]

Afternoon all,

On approach to some signals there is an OSS TPWS when the signal is red. Too fast and trip...

With a PoSA the TS TPWS is obviously not 'active' and you don't need to isolate the TPWS. However, is the OSS on approach still active ? Can it be tripped ? The signal is now considered 'clear' so there is no need to stop the train as the intention is that the signal will be passed.

I'm aware that with the PoSA it feels like the signal is Approach Controlled ? as you are almost brought to a stand before it flashes and you can hold back and it steps up with the PoSA.

Cheers in advance and technical corrections always welcomed

Com.

Yes and happens . Ill PM you.

 

[MarkyT]

Both OSS and TSS directly follow the aspect, so if the POSA has not yet cleared on approach then the signal is still considered at danger and the loops will still be active as you pass over them.

 

[ComUtoR]

as the area you are talking about is densely signalled.

I never mentioned where.. SPY !!

But, being the railway, and you’ve obviously asked for a reason, there will be an exception! And the core is low line speed..

Curiosity...

An OSS in a low speed area kinda threw me and I was curious as to why and that with a PoSA, I think, where it is approach controlled the OSS can still catch you if your unlucky and a fraction of a second before it steps up. I must admit I have changed my approach to the PoSA because you are too close when it steps up and it becomes an unnecessary distraction and cause of frustration, leading to loss of concentration.

ATO will be interesting.

Much love to the three of ya ♥♥♥

 

[bengley]

It's the same as when a subsidiary/associated position light signal is cleared - the OSS is still active. Generally as a rule I stick to 15mph on the approach even if the PoSA/sub is cleared where the signal has OSS

 

[edwin_m]

The OSS is designed to stop a train that's approaching too fast to stop within the overlap if its brakes are applied by the TSS at the signal. So if the train is going fast enough to trip the OSS and for the approach control conditions not to be satisfied by the time it gets there, I would have thought it's going too fast to be approaching a red aspect whether the POSA is lit or not.

 

[Highlandspring]

The OSS is designed to stop a train that's approaching too fast to stop within the overlap if its brakes are applied by the TSS at the signal.

*Pedant alert* The OSS is designed to stop the train before it reaches the first conflict point, which may or may not correspond to the length of the overlap.

 

[Kneedown]

Not related to POSA signals as such, but at some locations if a position light signal is cleared, the overspeed grids are still active, as a few Drivers have foumd out the hard way.

 

[theageofthetra]

How far out can you even see the POSA? - there are a few locations where a calling on can easily be confused with station or siding LED lights which diffuse badly in Networker windscreens.

Personally I would come to a stand at any red then treat the POSA no different to being called on or in a siding.

 

[carriageline]

I never mentioned where.. SPY !!

Hahaha fair enough!! I made assumptions from some of our previous convos!

Curiosity...

An OSS in a low speed area kinda threw me and I was curious as to why and that with a PoSA, I think, where it is approach controlled the OSS can still catch you if your unlucky and a fraction of a second before it steps up. I must admit I have changed my approach to the PoSA because you are too close when it steps up and it becomes an unnecessary distraction and cause of frustration, leading to loss of concentration.

ATO will be interesting.

Much love to the three of ya ♥♥♥

Shouldn’t make a difference in ATO (really). Train will travel to its end of movement authority (the signal), even with the POSA off. Once POSA off, train will be given an “on sight” movement authority. ATO requires Full Supervision and no less. Worse case is the train stops at the signal with the POSA flashing.

Plus, ATO won’t be using the TPWS anyway!

 

[ComUtoR]

How far out can you even see the POSA? - there are a few locations where a calling on can easily be confused with station or siding LED lights which diffuse badly in Networker windscreens.

The PoSA will flash. It is very obvious and hard to confuse with any other indication. If you can see the signal, you can see the PoSA. Where it is timed to release by approach control if you are driving towards the red normally you get to the AWS when it trips. You are annoyingly right at the point where you are stopping. (its deliberate) If you hang back it trips at a more reasonable distance.

Personally I would come to a stand at any red then treat the POSA no different to being called on or in a siding.

This is why ATO provides a benefit. Drivers can be overly defensive and so used to 'traditional' driving that it actually becomes more detrimental. The point of the PoSA is to speed up the system and prevent trains from stopping unnecessarily. It also stops the convo with the Signaller (a huge relief tbh). The first one I went through did throw me and you get a sense of panic but after the first few it becomes natural.

With a calling on you are prepared to stop short because you know you are going in permissive or into a sidings. We are almost programmed to act in a certain way with various expectations. With the PoSA there are a list of caveats before the Signaller pulls the road. I think that part of the issue with Drivers then making an error is because we have become so used to them that there is an element of overconfidence and previous experience that the next signal is green. It's still important to proceed at caution but put a little faith in the system... that just broke....

Hahaha fair enough!! I made assumptions from some of our previous convos!

Totally reasonable

We only have two areas with PoSAs. I am yet to get on through London Bridge yet.

Plus, ATO won’t be using the TPWS anyway!

If it effectively isolates the TPWS, what stops the train if the computer goes all T-1000 ? With no TPWS is Sarah Conner the Driver the only person who can therefore stop the unit ?

 

[Joseph_Locke]

If it effectively isolates the TPWS, what stops the train if the computer goes all T-1000 ? With no TPWS is Sarah Conner the Driver the only person who can therefore stop the unit ?

I would imagine it has a default sulk mode which causes it to brake harshly to a stand and play a recording of old George having a grumble about the idiots in the glass signal box over the PA.

 

[Supercoss]

Train stop deenergised
Arming & trigger loop still active at 22.2 mph so if you are motoring faster than that whilst proceeding on sight authority you will get a brake demand

 

[Supercoss]

 

[Supercoss]

A little wheelslip

 

[Supercoss]

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