Aspect Sequence exercise

[onestrangeday]

Hi Signalling Professional:

This is the first time I have tried an exercise for aspect sequence (single line and double line layout which I have done earlier) . can someone check my work ? and I would like see whether I am on the right track or not.



thanks

[PJW]

Just a quick initial glance of the presentation of sequence on screen without checking to layouts suggests are on right lines; nothing too awful such as a Green reading up to a Red.
Two things that immediately strike-
1. You have not shown any approach release. Where the speeds of a diverging route is different from the straight route, then the signal must be held at red (or in some specific cases at yellow) until the train has got sufficiently close so that driver can see both the route indication and the actua colour of the signal aspect- certainly needs to have received a caution aspect on the signal prior.
2. An aspect sequence chart is easier to read if you avoid depicting the lines completely vertically, but slope at a slight angle. Much clearer that chart reads right to left or left to right; also twhat is a "convergence" from two parallel signals in rear or what is a spreading out to reflect multiple routes from a junction signal. In particular on oe diagram you have joined both categories of the above in the same vertical line. It isn't actually incorrect but since the whole purpose of such a diagram is to give a pictorial readily assimilated depiction of the sequence, it rather loses the whole point if need to study hard to work out what is happening. In reality no real problem on such a simple layout, but as a matter of principle for application to more complicated sites then it is an important consideration. [Note that you will find many sequence charts on modern prjects do use the vertical lines- this I think happens because it is easier for the designer using CAD and saves a little space, but as a user it is definitely unhelpful, so much so that the diagrams rarely get used and everyone refers to the Control Tables- the easy to understand presentation showing the "whole picture" just fails to achieve its end and in my opinion we might as well not have them!]

Hi Signalling Professional:

This is the first time I have tried an exercise for aspect sequence (single line and double line layout which I have done earlier) . can someone check my work ? and I would like see whether I am on the right track or not.



thanks

[onestrangeday]

Hi PJW:

Thanks for your suggestion. I looked through the past model answer for aspect sequence, as you have already said they use either vertical or horizontal lines to show the aspect sequence. As for your experience, do they still use aspect sequence for the modern railway signalling system (such as Metro, High Speed Rail as most of its system uses distance to go principle) ?

One question to ask, you have mentioned about
‘You have not shown any approach release. Where the speeds of a diverging route is different from the straight route,’
if I want to show that on the aspect sequence, do I write such as”## OCC” , ##=name of the track circuit , OCC=approach release

Just a quick initial glance of the presentation of sequence on screen without checking to layouts suggests are on right lines; nothing too awful such as a Green reading up to a Red.
Two things that immediately strike-
1. You have not shown any approach release. Where the speeds of a diverging route is different from the straight route, then the signal must be held at red (or in some specific cases at yellow) until the train has got sufficiently close so that driver can see both the route indication and the actua colour of the signal aspect- certainly needs to have received a caution aspect on the signal prior.
2. An aspect sequence chart is easier to read if you avoid depicting the lines completely vertically, but slope at a slight angle. Much clearer that chart reads right to left or left to right; also twhat is a "convergence" from two parallel signals in rear or what is a spreading out to reflect multiple routes from a junction signal. In particular on oe diagram you have joined both categories of the above in the same vertical line. It isn't actually incorrect but since the whole purpose of such a diagram is to give a pictorial readily assimilated depiction of the sequence, it rather loses the whole point if need to study hard to work out what is happening. In reality no real problem on such a simple layout, but as a matter of principle for application to more complicated sites then it is an important consideration. [Note that you will find many sequence charts on modern prjects do use the vertical lines- this I think happens because it is easier for the designer using CAD and saves a little space, but as a user it is definitely unhelpful, so much so that the diagrams rarely get used and everyone refers to the Control Tables- the easy to understand presentation showing the "whole picture" just fails to achieve its end and in my opinion we might as well not have them!]

Hi Signalling Professional:

This is the first time I have tried an exercise for aspect sequence (single line and double line layout which I have done earlier) . can someone check my work ? and I would like see whether I am on the right track or not.



thanks

[PJW]

I'll perhaps annotate your examples when I get a chance, but you need to show a transition from one aspect (say red) to a better aspect occurring and against this show the condition which triggers this change. These are shown as vertical lines (and isanother reason for drawing the sequence lines horizontal and diagonal ather than vertical)- to distinguish more easily my preference is to show dashed. You will find several examples of this in attachments in other posts in this topic area.

Aspect sequence only appicable to lineside signalling and is of course rather different for a speed signalling system than the route signalling system (which itself is, when combined with the driver's "route knowledge" effectively a distance-to-go system) used in the UK.

Aspect sequence if all about how the necessary advanced warning is given to the driver when passing one signal as to the aspect displayed aat the subsequent one for situations in which unable to stop within the distance for which a signal is readable. On tramways and certain metros the speed is low enough, the train is light enough and has good enough brakes so it can be practicable just for a driver to see a red and stiop at it, in a similar way to driving a car. In that environment, o aspect sequence is necessary.

Hi PJW:

Thanks for your suggestion. I looked through the past model answer for aspect sequence, as you have already said they use either vertical or horizontal lines to show the aspect sequence. As for your experience, do they still use aspect sequence for the modern railway signalling system (such as Metro, High Speed Rail as most of its system uses distance to go principle) ?

One question to ask, you have mentioned about
‘You have not shown any approach release. Where the speeds of a diverging route is different from the straight route,’
if I want to show that on the aspect sequence, do I write such as”## OCC” , ##=name of the track circuit , OCC=approach release

Just a quick initial glance of the presentation of sequence on screen without checking to layouts suggests are on right lines; nothing too awful such as a Green reading up to a Red.
Two things that immediately strike-
1. You have not shown any approach release. Where the speeds of a diverging route is different from the straight route, then the signal must be held at red (or in some specific cases at yellow) until the train has got sufficiently close so that driver can see both the route indication and the actua colour of the signal aspect- certainly needs to have received a caution aspect on the signal prior.
2. An aspect sequence chart is easier to read if you avoid depicting the lines completely vertically, but slope at a slight angle. Much clearer that chart reads right to left or left to right; also twhat is a "convergence" from two parallel signals in rear or what is a spreading out to reflect multiple routes from a junction signal. In particular on oe diagram you have joined both categories of the above in the same vertical line. It isn't actually incorrect but since the whole purpose of such a diagram is to give a pictorial readily assimilated depiction of the sequence, it rather loses the whole point if need to study hard to work out what is happening. In reality no real problem on such a simple layout, but as a matter of principle for application to more complicated sites then it is an important consideration. [Note that you will find many sequence charts on modern prjects do use the vertical lines- this I think happens because it is easier for the designer using CAD and saves a little space, but as a user it is definitely unhelpful, so much so that the diagrams rarely get used and everyone refers to the Control Tables- the easy to understand presentation showing the "whole picture" just fails to achieve its end and in my opinion we might as well not have them!]

Hi Signalling Professional:

This is the first time I have tried an exercise for aspect sequence (single line and double line layout which I have done earlier) . can someone check my work ? and I would like see whether I am on the right track or not.



thanks

[PJW]

I think it is easier to discuss the single track layout; the double track layout as drawn has some signals which are underbraked (and indeed others which appear overbraked); it would be best to get to grips with more straight forward arrangement first.
The only issues on the single track layout are:
a) 11 is shown as a Red/Green not far in rear of 15 (similarly 13 and 17). Probably best not to provide 11- there is no absolute need to have a platform starting signal. If really need 11, then would need to make it "preceeded" by 15; i.e. prevent 11 for clearing unless 15 already cleared.
b) 55 should be a Red/Yellow rather than Red / Green and there should be a red light at the buffers.

I have shown on the attachment how to show the "MAR" Approach Release from Red for those routes which are the slower speed divergence through points. The really important thing to understand is that the signal is at red until the train has passed the previous signal, so the driver will see a yellow there.

I have also drawn out the area around 15/17 to 21 and again from 41 to the buffers (the middle section just repeats really). On your diagram, I can't tell really what is an approach release and what is a pure sequence.

I'll perhaps annotate your examples when I get a chance, but you need to show a transition from one aspect (say red) to a better aspect occurring and against this show the condition which triggers this change. These are shown as vertical lines (and is another reason for drawing the sequence lines horizontal and diagonal rather than vertical)- to distinguish more easily my preference is to show dashed. You will find several examples of this in attachments in other posts in this topic area.

Just a quick initial glance of the presentation of sequence on screen without checking to layouts suggests are on right lines; nothing too awful such as a Green reading up to a Red.
Two things that immediately strike-
1. You have not shown any approach release. Where the speeds of a diverging route is different from the straight route, then the signal must be held at red (or in some specific cases at yellow) until the train has got sufficiently close so that driver can see both the route indication and the actua colour of the signal aspect- certainly needs to have received a caution aspect on the signal prior.
2. An aspect sequence chart is easier to read if you avoid depicting the lines completely vertically, but slope at a slight angle. Much clearer that chart reads right to left or left to right; also twhat is a "convergence" from two parallel signals in rear or what is a spreading out to reflect multiple routes from a junction signal. In particular on oe diagram you have joined both categories of the above in the same vertical line. It isn't actually incorrect but since the whole purpose of such a diagram is to give a pictorial readily assimilated depiction of the sequence, it rather loses the whole point if need to study hard to work out what is happening. In reality no real problem on such a simple layout, but as a matter of principle for application to more complicated sites then it is an important consideration. [Note that you will find many sequence charts on modern prjects do use the vertical lines- this I think happens because it is easier for the designer using CAD and saves a little space, but as a user it is definitely unhelpful, so much so that the diagrams rarely get used and everyone refers to the Control Tables- the easy to understand presentation showing the "whole picture" just fails to achieve its end and in my opinion we might as well not have them!]

Hi Signalling Professional:

This is the first time I have tried an exercise for aspect sequence (single line and double line layout which I have done earlier) . can someone check my work ? and I would like see whether I am on the right track or not.

thanks

[onestrangeday]

Hi PJW:

thanks for your review. You have mentioned about the attachment, but I don't see it.

I have few questions though:

"a) 11 is shown as a Red/Green not far in rear of 15 (similarly 13 and 17). Probably best not to provide 11- there is no absolute need to have a platform starting signal. If really need 11, then would need to make it "preceeded" bt 15; i.e. prevent 11 for clearing unless 15 already cleared."

Q1: If in this case the platform is very close to the points area, can I eliminate the junction indicator, instead place at the platform with the starting signal ?

or if you eliminate the platform starting signal, how do you show to the driver when to proceed ? (how does this done in UK ?) with signs, or order from train controller ?

Q2:
"I have shown on the attachment how to show the "MAR" Approach Release from Red for those routes which are the slower speed divergence through points."

what is "MAR" Approach release ?



thanks

I think it is easier to discuss the single track layout; the double track layout as drawn has some signals which are underbraked (and indeed others which appear overbraked); it would be best to get to grips with more straight forward arrangement first.
The only issues on the single track layout are:
a) 11 is shown as a Red/Green not far in rear of 15 (similarly 13 and 17). Probably best not to provide 11- there is no absolute need to have a platform starting signal. If really need 11, then would need to make it "preceeded" bt 15; i.e. prevent 11 for clearing unless 15 already cleared.
b) 55 should be a Red/Yellow rather than Red / Green and there should be a red light at the buffers.

I have shown on the attachment how to show the "MAR" Approach Release from Red for those routes which are the slower speed divergence through points. The really important thing to understand is that the signal is at red until the train has passed the previous signal, so the driver will see a yellow there.

I have also drawn out the area around 15/17 to 23/25. On your diagram, can't tell really what is an approach release and what is a pure sequence.

I'll perhaps annotate your examples when I get a chance, but you need to show a transition from one aspect (say red) to a better aspect occurring and against this show the condition which triggers this change. These are shown as vertical lines (and is another reason for drawing the sequence lines horizontal and diagonal rather than vertical)- to distinguish more easily my preference is to show dashed. You will find several examples of this in attachments in other posts in this topic area.

Just a quick initial glance of the presentation of sequence on screen without checking to layouts suggests are on right lines; nothing too awful such as a Green reading up to a Red.
Two things that immediately strike-
1. You have not shown any approach release. Where the speeds of a diverging route is different from the straight route, then the signal must be held at red (or in some specific cases at yellow) until the train has got sufficiently close so that driver can see both the route indication and the actua colour of the signal aspect- certainly needs to have received a caution aspect on the signal prior.
2. An aspect sequence chart is easier to read if you avoid depicting the lines completely vertically, but slope at a slight angle. Much clearer that chart reads right to left or left to right; also twhat is a "convergence" from two parallel signals in rear or what is a spreading out to reflect multiple routes from a junction signal. In particular on oe diagram you have joined both categories of the above in the same vertical line. It isn't actually incorrect but since the whole purpose of such a diagram is to give a pictorial readily assimilated depiction of the sequence, it rather loses the whole point if need to study hard to work out what is happening. In reality no real problem on such a simple layout, but as a matter of principle for application to more complicated sites then it is an important consideration. [Note that you will find many sequence charts on modern prjects do use the vertical lines- this I think happens because it is easier for the designer using CAD and saves a little space, but as a user it is definitely unhelpful, so much so that the diagrams rarely get used and everyone refers to the Control Tables- the easy to understand presentation showing the "whole picture" just fails to achieve its end and in my opinion we might as well not have them!]

Hi Signalling Professional:

This is the first time I have tried an exercise for aspect sequence (single line and double line layout which I have done earlier) . can someone check my work ? and I would like see whether I am on the right track or not.

thanks

[PJW]

Neither do I now. Sorry no time to resolve now- will address this evening I hope

Hi PJW:

thanks for your review. You have mentioned about the attachment, but I don't see it.

I have few questions though:

"a) 11 is shown as a Red/Green not far in rear of 15 (similarly 13 and 17). Probably best not to provide 11- there is no absolute need to have a platform starting signal. If really need 11, then would need to make it "preceeded" bt 15; i.e. prevent 11 for clearing unless 15 already cleared."

Q1: If in this case the platform is very close to the points area, can I eliminate the junction indicator, instead place at the platform with the starting signal ?

or if you eliminate the platform starting signal, how do you show to the driver when to proceed ? (how does this done in UK ?) with signs, or order from train controller ?

Q2:
"I have shown on the attachment how to show the "MAR" Approach Release from Red for those routes which are the slower speed divergence through points."

what is "MAR" Approach release ?



thanks

I think it is easier to discuss the single track layout; the double track layout as drawn has some signals which are underbraked (and indeed others which appear overbraked); it would be best to get to grips with more straight forward arrangement first.
The only issues on the single track layout are:
a) 11 is shown as a Red/Green not far in rear of 15 (similarly 13 and 17). Probably best not to provide 11- there is no absolute need to have a platform starting signal. If really need 11, then would need to make it "preceeded" bt 15; i.e. prevent 11 for clearing unless 15 already cleared.
b) 55 should be a Red/Yellow rather than Red / Green and there should be a red light at the buffers.

I have shown on the attachment how to show the "MAR" Approach Release from Red for those routes which are the slower speed divergence through points. The really important thing to understand is that the signal is at red until the train has passed the previous signal, so the driver will see a yellow there.

I have also drawn out the area around 15/17 to 23/25. On your diagram, can't tell really what is an approach release and what is a pure sequence.

I'll perhaps annotate your examples when I get a chance, but you need to show a transition from one aspect (say red) to a better aspect occurring and against this show the condition which triggers this change. These are shown as vertical lines (and is another reason for drawing the sequence lines horizontal and diagonal rather than vertical)- to distinguish more easily my preference is to show dashed. You will find several examples of this in attachments in other posts in this topic area.

Just a quick initial glance of the presentation of sequence on screen without checking to layouts suggests are on right lines; nothing too awful such as a Green reading up to a Red.
Two things that immediately strike-
1. You have not shown any approach release. Where the speeds of a diverging route is different from the straight route, then the signal must be held at red (or in some specific cases at yellow) until the train has got sufficiently close so that driver can see both the route indication and the actua colour of the signal aspect- certainly needs to have received a caution aspect on the signal prior.
2. An aspect sequence chart is easier to read if you avoid depicting the lines completely vertically, but slope at a slight angle. Much clearer that chart reads right to left or left to right; also twhat is a "convergence" from two parallel signals in rear or what is a spreading out to reflect multiple routes from a junction signal. In particular on oe diagram you have joined both categories of the above in the same vertical line. It isn't actually incorrect but since the whole purpose of such a diagram is to give a pictorial readily assimilated depiction of the sequence, it rather loses the whole point if need to study hard to work out what is happening. In reality no real problem on such a simple layout, but as a matter of principle for application to more complicated sites then it is an important consideration. [Note that you will find many sequence charts on modern prjects do use the vertical lines- this I think happens because it is easier for the designer using CAD and saves a little space, but as a user it is definitely unhelpful, so much so that the diagrams rarely get used and everyone refers to the Control Tables- the easy to understand presentation showing the "whole picture" just fails to achieve its end and in my opinion we might as well not have them!]

[onestrangeday]

Hi PJW:

Sure no worries, I am not in hurry, take your time. I just only ask for making sure my thinking is on the track or not.

Once again thanks for your reply.



thanks

Neither do I now. Sorry no time to resolve now- will address this evening I hope

Hi PJW:

thanks for your review. You have mentioned about the attachment, but I don't see it.

I have few questions though:

"a) 11 is shown as a Red/Green not far in rear of 15 (similarly 13 and 17). Probably best not to provide 11- there is no absolute need to have a platform starting signal. If really need 11, then would need to make it "preceeded" bt 15; i.e. prevent 11 for clearing unless 15 already cleared."

Q1: If in this case the platform is very close to the points area, can I eliminate the junction indicator, instead place at the platform with the starting signal ?

or if you eliminate the platform starting signal, how do you show to the driver when to proceed ? (how does this done in UK ?) with signs, or order from train controller ?

Q2:
"I have shown on the attachment how to show the "MAR" Approach Release from Red for those routes which are the slower speed divergence through points."

what is "MAR" Approach release ?



thanks

I think it is easier to discuss the single track layout; the double track layout as drawn has some signals which are underbraked (and indeed others which appear overbraked); it would be best to get to grips with more straight forward arrangement first.
The only issues on the single track layout are:
a) 11 is shown as a Red/Green not far in rear of 15 (similarly 13 and 17). Probably best not to provide 11- there is no absolute need to have a platform starting signal. If really need 11, then would need to make it "preceeded" bt 15; i.e. prevent 11 for clearing unless 15 already cleared.
b) 55 should be a Red/Yellow rather than Red / Green and there should be a red light at the buffers.

I have shown on the attachment how to show the "MAR" Approach Release from Red for those routes which are the slower speed divergence through points. The really important thing to understand is that the signal is at red until the train has passed the previous signal, so the driver will see a yellow there.

I have also drawn out the area around 15/17 to 23/25. On your diagram, can't tell really what is an approach release and what is a pure sequence.

I'll perhaps annotate your examples when I get a chance, but you need to show a transition from one aspect (say red) to a better aspect occurring and against this show the condition which triggers this change. These are shown as vertical lines (and is another reason for drawing the sequence lines horizontal and diagonal rather than vertical)- to distinguish more easily my preference is to show dashed. You will find several examples of this in attachments in other posts in this topic area.

[PJW]

Q1.
Yes you could put the PLJI on signal 11 and not have 15 at all.
Depending on distance to 21, probably 11 would be a 2 aspect Red/ Green and a Yellow/Green signal would be needed placed braking distance prior to 21.
Wouldn't want the protecting signal too far from the points it protects though, so alternatively 11 could be positioned in position of 15.
Probably driver from station A could see it and choose not to leave the station whilst at red; however it is generally not necessary that there be a signal at the end of every platform. Where a station platform is mid-section, then the driver just restarts their train continuing in the same direction as before. No signs, no instuctions (other than where there has to be a train guard to confirm all doors closed safely if they are not power operated, interlocked with the train and the driver has visibillity of external of train via mirrors or CCTV monitors).

There is a need though to provide a signal "at place of reversal"- the driver cannot restart in the opposite direction to the origial one without a signal which authorises this. So in this case since trains terminate and reverse direction at station A ,then it would be a good idea to have signals at the platform end or at least relatively close to it, certainly visible from it.


Q2.
"Approach Release" means that the signal is deliberately initially held at a more restrictive aspect than its "true" aspect relative to the aspect displayed by the one beyond it. It is a disadvantage of "route signalling", it is over-restrictive and reduces capacity and indeed can be a "SPAD trap" for the driver. However it is necessary because the alternative of not doing it is worse!

Consider the situation if this were not applied- a signal such as 21 would show Green with PLJI when routed up to 23 at Green. That would itself mean that the signal 17 would also show Green. The driver of the train would then get the same aspect sequence initially as if 21 had been set on the straight route via 25. Therefore driver would be coming fast and see 21 in the distance at Green still expecting to go straight on; then much later the driver would notice that it also displayed a PLJI and that train needed to go via the loop points. These may only be 25mph rather than say 80mph for the straight route; driver would not be able to slow sufficiently in the available length and hence the train would overspeed at the junction and would likely derail.

Instead we hold 21 at Red, so that driver gets a Yellow at 17 and therefore expects to stop at 21. Therefore when we eventually allow 21 to clear (i.e. "approach release from red") the driver may be typically 400m from it with the brakes on expecting to stop at it, but then sees it clear to Green + PLJI and thus accelerates again so that pass over the points at the safe speed. Over restrictive but safe. Not too bad for 25mph points but much less desirale if the points permit 50mph divergence- the signalling would prevent this opportunity being achieved in practice. Hence in such situations would probably implement "approach release from yellow"; however even this is not ideal but it is basically what the UK are stuck with until we change to ETCS which is a from of "speed signalling".

Does this help you understand?

Hi PJW:

Sure no worries, I am not in hurry, take your time. I just only ask for making sure my thinking is on the track or not.

Once again thanks for your reply.



thanks


I have few questions though:

"a) 11 is shown as a Red/Green not far in rear of 15 (similarly 13 and 17). Probably best not to provide 11- there is no absolute need to have a platform starting signal. If really need 11, then would need to make it "preceeded" bt 15; i.e. prevent 11 for clearing unless 15 already cleared."

Q1: If in this case the platform is very close to the points area, can I eliminate the junction indicator, instead place at the platform with the starting signal ?

or if you eliminate the platform starting signal, how do you show to the driver when to proceed ? (how does this done in UK ?) with signs, or order from train controller ?

Q2:
"I have shown on the attachment how to show the "MAR" Approach Release from Red for those routes which are the slower speed divergence through points."

what is "MAR" Approach release ?

thanks

[PJW]

Here is my attachment to compare presentation to your orginal.
I think I had too large a file size before.

Note that I have assumed that signals 11,15 and 13,17 all exist.
Actually because there are slower speed diverging routes from 15 & 17 it isn't enough just to say the rear signals cannot clear until the forward signals are off, as these themselves would have to be approach released.
Potentially could make the condition as "ready to clear" rather than "off" but that is a complication best avoided at this stage of learning.

Hence I have given 11 & 13 yellow aspects which would themselves need to be approach released (but note that their Greens would be shown when 15/17 showing Green and would NOT be approach released) because of the underbraking. However as stated in earlier reply, better not to have all those signals.

Conversely since 15/17 to 21 is overbraked then I have assumed that for the branch that the 3 aspect signals do not show their yellow and that there is an extra signal 19 to act as a distant for 21.

Modified attachment to show the A/R for 11 & 13 more clearly