another try at double line layout

[onestrangeday]

Hi Signalling Professionals:

Here is another exercise attempt I have done for a double line layout I hope I am on the right track. Any comments and suggestions are highly appreciated and welcomed.

For the Question 4, can anyone provide comments on how to approach the question? I have looked though the ‘railway signalling’ textbook (page 20~27) that it has only described the method for calculating the headway for a stopping trains, but does not have description on the signal spacing for stopping trains, so I hope someone can provide any suggestions on this.

In my learning experience, I’ve learnt that the (max & min) signal spacing is determined from the type of signalling system used (using the 2,3,4 aspect formula) to see whether it meets the headway requirement defined by the customer.


Thanks

[PJW]

Layout:
1. You should also have shown the signals on the approach to 11 and 13, particularly as signal 13 is placed so close to the junction that the points must be within its locked overlap and there obviously has to be an "acceptance home" at which trains can be held awaiting the conflicting movement to pass clear of the junction.

2. Signal 12 seems to be too close to junction- ideally would want the rear of any train held at it not to trail back and prevent other train movements over the junction.

3. You have signalled both lines bidirectionally from this junction. Not wrong and the facing & trailing crossovers do suggest use of the platforms at A for turning back trains at least. In the UK bi-di signalling like this is rare, though actually with more recent thoughts and "modular signalling" will become more common. However for this exercise re headway I don't think it is needed and thinking re the exam then it would be unnecessary and consume valuable time.

4. Very sensible to leave gap in numbering system for the Not To Scale potions. However does imply only 1 "missing signal". The distance between scale portions is 4km and if providing continuous 3 aspect signalling then would require signals spaced reasonably equally, separated by at least braking distance but not too much more than that amount. There would probably be more signals (based on the other signals shown on this plan, but see item 5) and therefore should either have calculated, indicated their positions and numbered signals accordingly, or perhaps have used a separate numbering sequence at each "island" of signalling- could have used prefixes A, B, C etc. according to the station related.

5. For those signals you have shown, it looks like you are spacing at 500m - 700m yet you calculate braking distance as 2000m. Need to explain / rationalise.
If we say there is a signal 17 midway between 15 and 19 then this would be ok, but in that case 19 would not be braking distance from 23. This is possible but would need special controls Another possibility would be not to have a signal 19 but use 23 instead, if 17-23 a distance which isn't too excessive. Alternatively perhaps eliminate 23. Need to look at the calculations before determining course of action here.

6.Certainly do not need signal 36; the line is shown as uni-directional by the arrows. Also should place some signals on this end of the plan. Station C itself does need the signalling you have shown to permit the reversal of passenger trains requested; also needs some signals to permit running round of freight trains and that means getting a loc to rejoin the other end of its train and therefore a permissive movement.

=====================================================
Re calculations of non-stop and stopping headways:
a) look at other threads in this section of the website http://www.irseexam.co.uk/forum-45-page-1.html

b) Look at the Appendix G of the IRSE Module 2 Study Pack on the DVD you get when registering to sit the exam. This is a much updated version of the old "IRSE Green Book" number 13.

However the "Railway Signalling" textbook you quote does indeed have details of the calculation of stopping headway from page 22 to 25 and it is the non-stopping that is covered on pages 8 - 11.
=====================================================
To clarify:
MINIMUM signal spacing is set by BRAKING from HIGHEST PERMISSIBLE speed (directly in the case of 3 aspects, between ALTERNATE signals in the case of 4 aspects)

MAXIMUM signal spacing set by the more restrictive of:
a) the acceptable levels of over-braking (often 133 or 150 percent)
b) the HEADWAY requirement.

I'll look at your numbers separately.

Hi Signalling Professionals:

Here is another exercise attempt I have done for a double line layout I hope I am on the right track. Any comments and suggestions are highly appreciated and welcomed.

For the Question 4, can anyone provide comments on how to approach the question? I have looked though the ‘railway signalling’ textbook (page 20~27) that it has only described the method for calculating the headway for a stopping trains, but does not have description on the signal spacing for stopping trains, so I hope someone can provide any suggestions on this.

In my learning experience, I’ve learnt that the (max & min) signal spacing is determined from the type of signalling system used (using the 2,3,4 aspect formula) to see whether it meets the headway requirement defined by the customer.


Thanks

[onestrangeday]

Hi PJW:

Thanks for taking time to review my work. I have learnt much from the comment you gave, and I think I need to think about it again.
My reply to your comments as below:

1. I have shifted the signal 13 further apart from the points area, as to make sure that the overlap distance does not included the points I think this shall be the best choices.

2. I agree, so I have moved the signal 12 into the Not Scale potions as to make sure it will not interfere other train movements over the junction.

3. I agree with you, it is not always profitable to implement bi-directional signalling system on the railway network, it’s definitely cost much. So I changed to only using one direction signalling system for station A& B, but bi-directional signalling system for station C as to allows reversal and running around movement of passenger train and freight trains.

4. I agree with you I have re-number the signal on the layout as to leave spare signals for future usage.

5. I am not sure whether my braking distance calculation is suitable or not. As stated from the question that the permitted Passenger speeds is 160km/h. (I’ve taken this figure as my braking distance calculation taking the worst case scenario into calculation), and the braking distance calculated from this is approximately 2km as shown from my calculation. However, the question also says that the required headway for following stopping trains at 120km/h is 6 min, and the non-stopping trains at 120km/h are 3 min. Or shall I taken 120km/h for the braking distance calculation and as the minimum signal spacing?

And when it comes to place signals at station area, we do not place signals 2km apart right? (As for station B there would not have such space available and for station C the station area is less than 2km (from 17.800 km~ 18.450). So I believe the signals in the station area are sometimes not be able to be placed for full service braking distance apart (home & starting signals).

So how should we place the signals at terminal as to suit headway requirement?
Sorry to ask some silly questions as above.

But as I have learnt in the past, when it comes to place signals at terminal. General speaking, we should place home and starting signals at terminals (for entering and leaving the platform area) and they shall be as close as possible to allow quick clearing of signals once train have left the terminal area. Also place junction signals before points area and make sure it’s overlap will not prevent the operation of point area as for the best choice. (But this may be always be possible due to civil constraints etc.)

If took 120km/h for calculation, the braking distance is approximately 1200m.

6. Sure, I have re-signaled the layout for reversal of passenger trains and running round of freight trains. Can you check whether it is appropriate?

I will read through other thread about how to calculate the signal spacing for a stopping train at station area for Question 4, if I have further questions I will ask again.


Attached layout is the revised version.



Thank you for taking time to correct my work

Layout:
1. You should also have shown the signals on the approach to 11 and 13, particularly as signal 13 is placed so close to the junction that the points must be within its locked overlap and there obviously has to be an "acceptance home" at which trains can be held awaiting the conflicting movement to pass clear of the junction.

2. Signal 12 seems to be too close to junction- ideally would want the rear of any train held at it not to trail back and prevent other train movements over the junction.

3. You have signalled both lines bidirectionally from this junction. Not wrong and the facing & trailing crossovers do suggest use of the platforms at A for turning back trains at least. In the UK bi-di signalling like this is rare, though actually with more recent thoughts and "modular signalling" will become more common. However for this exercise re headway I don't think it is needed and thinking re the exam then it would be unnecessary and consume valuable time.

4. Very sensible to leave gap in numbering system for the Not To Scale potions. However does imply only 1 "missing signal". The distance between scale portions is 4km and if providing continuous 3 aspect signalling then would require signals spaced reasonably equally, separated by at least braking distance but not too much more than that amount. There would probably be more signals (based on the other signals shown on this plan, but see item 5) and therefore should either have calculated, indicated their positions and numbered signals accordingly, or perhaps have used a separate numbering sequence at each "island" of signalling- could have used prefixes A, B, C etc. according to the station related.

5. For those signals you have shown, it looks like you are spacing at 500m - 700m yet you calculate braking distance as 2000m. Need to explain / rationalise.
If we say there is a signal 17 midway between 15 and 19 then this would be ok, but in that case 19 would not be braking distance from 23. This is possible but would need special controls Another possibility would be not to have a signal 19 but use 23 instead, if 17-23 a distance which isn't too excessive. Alternatively perhaps eliminate 23. Need to look at the calculations before determining course of action here.

6.Certainly do not need signal 36; the line is shown as uni-directional by the arrows. Also should place some signals on this end of the plan. Station C itself does need the signalling you have shown to permit the reversal of passenger trains requested; also needs some signals to permit running round of freight trains and that means getting a loc to rejoin the other end of its train and therefore a permissive movement.

=====================================================
Re calculations of non-stop and stopping headways:
a) look at other threads in this section of the website http://www.irseexam.co.uk/forum-45-page-1.html

b) Look at the Appendix G of the IRSE Module 2 Study Pack on the DVD you get when registering to sit the exam. This is a much updated version of the old "IRSE Green Book" number 13.

However the "Railway Signalling" textbook you quote does indeed have details of the calculation of stopping headway from page 22 to 25 and it is the non-stopping that is covered on pages 8 - 11.
=====================================================
To clarify:
MINIMUM signal spacing is set by BRAKING from HIGHEST PERMISSIBLE speed (directly in the case of 3 aspects, between ALTERNATE signals in the case of 4 aspects)

MAXIMUM signal spacing set by the more restrictive of:
a) the acceptable levels of over-braking (often 133 or 150 percent)
b) the HEADWAY requirement.

I'll look at your numbers separately.

Hi Signalling Professionals:

Here is another exercise attempt I have done for a double line layout I hope I am on the right track. Any comments and suggestions are highly appreciated and welcomed.

For the Question 4, can anyone provide comments on how to approach the question? I have looked though the ‘railway signalling’ textbook (page 20~27) that it has only described the method for calculating the headway for a stopping trains, but does not have description on the signal spacing for stopping trains, so I hope someone can provide any suggestions on this.

In my learning experience, I’ve learnt that the (max & min) signal spacing is determined from the type of signalling system used (using the 2,3,4 aspect formula) to see whether it meets the headway requirement defined by the customer.


Thanks

[PJW]

No such thing as a silly question; actually you are asking all the right ones. This is exactly what the website is for.

1-4. Yes you have clearly understood what I was explaining.

5. Not yet myself looked at calculations. Hopefully later today.

However yes in a station area there is often a need to have signals closer than would be permitted by having 3 aspect signals at the braking distance apart, particularly as in this case when it is so long.
Therefore need to something a bit special, which could be:
a) signal as a "mechanical area" with one distant signal for all the signals for one direction at that site- the various "homes" and "starters" would be red/green and the only separation which needs to be at braking is from the distant to the first of them,
b) signal with 3 aspect MAS but impose approach release conditions "modified 3 aspect sequence" to ensure that when signals too close that the train speed has already been brought down low enough such that there is then braking at that speed,
c) have an area of 4 aspect signalling
d) reduce the permissible speed in the area (which is obviously the solution which best fits terminal stations).

I was slightly alluding to this scenario as a very subtle hint in my earlier reply. I think we need to study the calculations first, then return to this topic.

Not all railways would adopt all of the above solutions a-d; hence this raises the question:
"which railway's practices are you attempting to follow"?

This I accept may be a hard one for you to answer given that your experience isn't with such signalling at all. If you are using IRSE publications then generally these reflect UK practice, but perhaps from your geographic location there is influence from Australia? Much is similar but there are differences and indeed from one Australian state to another. I am no expert on this but I have been given access to some of their standards and have a few contacts from whom I could seek advice if this were the case. Otherwise if you are just trying to learn "a version" then probably best to stick generally to the UK approach. Problem is that when you are learning it can be unnecessarily confusing to be introduced to many variants before one is clearly established in the mind.

Hi PJW:

Thanks for taking time to review my work. I have learnt much from the comment you gave, and I think I need to think about it again.
My reply to your comments as below:

1. I have shifted the signal 13 further apart from the points area, as to make sure that the overlap distance does not included the points I think this shall be the best choices.

2. I agree, so I have moved the signal 12 into the Not Scale potions as to make sure it will not interfere other train movements over the junction.

3. I agree with you, it is not always profitable to implement bi-directional signalling system on the railway network, it’s definitely cost much. So I changed to only using one direction signalling system for station A& B, but bi-directional signalling system for station C as to allows reversal and running around movement of passenger train and freight trains.

4. I agree with you I have re-number the signal on the layout as to leave spare signals for future usage.

5. I am not sure whether my braking distance calculation is suitable or not. As stated from the question that the permitted Passenger speeds is 160km/h. (I’ve taken this figure as my braking distance calculation taking the worst case scenario into calculation), and the braking distance calculated from this is approximately 2km as shown from my calculation. However, the question also says that the required headway for following stopping trains at 120km/h is 6 min, and the non-stopping trains at 120km/h are 3 min. Or shall I taken 120km/h for the braking distance calculation and as the minimum signal spacing?

And when it comes to place signals at station area, we do not place signals 2km apart right? (As for station B there would not have such space available and for station C the station area is less than 2km (from 17.800 km~ 18.450). So I believe the signals in the station area are sometimes not be able to be placed for full service braking distance apart (home & starting signals).

So how should we place the signals at terminal as to suit headway requirement?
Sorry to ask some silly questions as above.

But as I have learnt in the past, when it comes to place signals at terminal. General speaking, we should place home and starting signals at terminals (for entering and leaving the platform area) and they shall be as close as possible to allow quick clearing of signals once train have left the terminal area. Also place junction signals before points area and make sure it’s overlap will not prevent the operation of point area as for the best choice. (But this may be always be possible due to civil constraints etc.)

If took 120km/h for calculation, the braking distance is approximately 1200m.

6. Sure, I have re-signaled the layout for reversal of passenger trains and running round of freight trains. Can you check whether it is appropriate?

I will read through other thread about how to calculate the signal spacing for a stopping train at station area for Question 4, if I have further questions I will ask again.

Attached layout is the revised version.

Thank you for taking time to correct my work

[PJW]

Not sure what happened to the text I posted earlier as it all seems blank to me, so repeating it!

No such thing as a silly questions; yours's are actually very pertinent and exactly what should be asked on this Forum.

Items 1-4. Yes you have shown you have understood my earlier comments.

Item 5.
Yes you are right; you will signals closer than braking distance to each other in the vicinity of stations, particularly with a 2km braking distance. Therefore plain simple 3 aspect MAS is not suitable; I did drop a very subtle hint to that effect in my earlier response. I think we need to look at the calculations first before getting into this consideration, but it is obviously imporrtant to return to it.

The possible options:
1. Provide one distant signal (yellow/green) at braking distance from the first home (red/green), but that applies to the whole group of signals for that direction at the site. Fundamentally implementing "mechanical semaphore" principles using colour lights and needing the bring a train under control at each signal before allowing it to clear up to the next signal (so that the lack of full braking between subsequent signals is not relevant)
2. Provide 3 aspect signals that are not all at braking distance apart but using "modified 3 aspect sequnce" which imposes approach release cnditions on thse that are insufficiently spaced. Similar to 1; effectively the train is slowed doewn to a speed such that there is then braking distance from that yellow to the next signal at red.
3. Provide an area of 4 aspect signalling so that there only has to be braking between alternate ones.
4. Impose a permanent speed restriction to reduce the speed at which the braking distance is calculated; this is most suitable for lines approaching a terminal station of course.

Not all these solutions are applicable to all railways so before going more deeply into this, need to know which railway's principles yu'll be following. Accept this is difficult question for you, given your experience is in in-cab signalling. As Jerry has written in the other post, you can certainly sit the exam just familiar with your own railways practices so don't feel forced to learn lineside signalling; however I guess you want to to broaden your experience and this has surely got to be a good thing so I'd encourage.
The IRSE material generally follows UK mainline practice (much of it is 1980s and reflects British Railways, some things have changed during my career but overall Network Rail isn't hugely different). Hence unless there is good reason I'd recommend adopting, but if say you were more likely to be familiar with Australian practice then we could discuss that. I am afraid that I am not an expert in it, but have acquired some useful material and I do have a few contacts from whom I could seek advice and clarification. Railways do face different environments, traffic conditions, cultures and each have had their own accidents, so there are idfferences; indeed there are some significant differences I believe between the various Australian states. Let me know if there is any reason for you to adopt any set of rules other than BR/NR's before we discuss this more.

I'll look at your calculations separately.

Hi PJW:

Thanks for taking time to review my work. I have learnt much from the comment you gave, and I think I need to think about it again.
My reply to your comments as below:

1. I have shifted the signal 13 further apart from the points area, as to make sure that the overlap distance does not included the points I think this shall be the best choices.

2. I agree, so I have moved the signal 12 into the Not Scale potions as to make sure it will not interfere other train movements over the junction.

3. I agree with you, it is not always profitable to implement bi-directional signalling system on the railway network, it’s definitely cost much. So I changed to only using one direction signalling system for station A& B, but bi-directional signalling system for station C as to allows reversal and running around movement of passenger train and freight trains.

4. I agree with you I have re-number the signal on the layout as to leave spare signals for future usage.

5. I am not sure whether my braking distance calculation is suitable or not. As stated from the question that the permitted Passenger speeds is 160km/h. (I’ve taken this figure as my braking distance calculation taking the worst case scenario into calculation), and the braking distance calculated from this is approximately 2km as shown from my calculation. However, the question also says that the required headway for following stopping trains at 120km/h is 6 min, and the non-stopping trains at 120km/h are 3 min. Or shall I taken 120km/h for the braking distance calculation and as the minimum signal spacing?

And when it comes to place signals at station area, we do not place signals 2km apart right? (As for station B there would not have such space available and for station C the station area is less than 2km (from 17.800 km~ 18.450). So I believe the signals in the station area are sometimes not be able to be placed for full service braking distance apart (home & starting signals).

So how should we place the signals at terminal as to suit headway requirement?
Sorry to ask some silly questions as above.

But as I have learnt in the past, when it comes to place signals at terminal. General speaking, we should place home and starting signals at terminals (for entering and leaving the platform area) and they shall be as close as possible to allow quick clearing of signals once train have left the terminal area. Also place junction signals before points area and make sure it’s overlap will not prevent the operation of point area as for the best choice. (But this may be always be possible due to civil constraints etc.)

If took 120km/h for calculation, the braking distance is approximately 1200m.

6. Sure, I have re-signaled the layout for reversal of passenger trains and running round of freight trains. Can you check whether it is appropriate?

I will read through other thread about how to calculate the signal spacing for a stopping train at station area for Question 4, if I have further questions I will ask again.

Attached layout is the revised version.

Thank you for taking time to correct my work

[onestrangeday]

Hi PJW:

thanks for your suggestions it gives me another thought about how I should tackle this question.

I have tried to looked through the past IRSE exam papers, and I have modified my approach to the questions as shown from my attached version 1 file. Please check my work to see whether it is correct or not.

I am still having trouble to find methods about how to do the Question 4, but I will try to dig any past of the IRSE exam papers to see whether there is similiar questions or not. I will post my attempt again for you to check and see whether I am on the right track or not.

Basically I will say I will follow the British Practice just to braoden my view on other railway environment.



thanks for taking time to check

Not sure what happened to the text I posted earlier as it all seems blank to me, so repeating it!

No such thing as a silly questions; yours's are actually very pertinent and exactly what should be asked on this Forum.

Items 1-4. Yes you have shown you have understood my earlier comments.

Item 5.
Yes you are right; you will signals closer than braking distance to each other in the vicinity of stations, particularly with a 2km braking distance. Therefore plain simple 3 aspect MAS is not suitable; I did drop a very subtle hint to that effect in my earlier response. I think we need to look at the calculations first before getting into this consideration, but it is obviously imporrtant to return to it.

The possible options:
1. Provide one distant signal (yellow/green) at braking distance from the first home (red/green), but that applies to the whole group of signals for that direction at the site. Fundamentally implementing "mechanical semaphore" principles using colour lights and needing the bring a train under control at each signal before allowing it to clear up to the next signal (so that the lack of full braking between subsequent signals is not relevant)
2. Provide 3 aspect signals that are not all at braking distance apart but using "modified 3 aspect sequnce" which imposes approach release cnditions on thse that are insufficiently spaced. Similar to 1; effectively the train is slowed doewn to a speed such that there is then braking distance from that yellow to the next signal at red.
3. Provide an area of 4 aspect signalling so that there only has to be braking between alternate ones.
4. Impose a permanent speed restriction to reduce the speed at which the braking distance is calculated; this is most suitable for lines approaching a terminal station of course.

Not all these solutions are applicable to all railways so before going more deeply into this, need to know which railway's principles yu'll be following. Accept this is difficult question for you, given your experience is in in-cab signalling. As Jerry has written in the other post, you can certainly sit the exam just familiar with your own railways practices so don't feel forced to learn lineside signalling; however I guess you want to to broaden your experience and this has surely got to be a good thing so I'd encourage.
The IRSE material generally follows UK mainline practice (much of it is 1980s and reflects British Railways, some things have changed during my career but overall Network Rail isn't hugely different). Hence unless there is good reason I'd recommend adopting, but if say you were more likely to be familiar with Australian practice then we could discuss that. I am afraid that I am not an expert in it, but have acquired some useful material and I do have a few contacts from whom I could seek advice and clarification. Railways do face different environments, traffic conditions, cultures and each have had their own accidents, so there are idfferences; indeed there are some significant differences I believe between the various Australian states. Let me know if there is any reason for you to adopt any set of rules other than BR/NR's before we discuss this more.

I'll look at your calculations separately.

Hi PJW:

Thanks for taking time to review my work. I have learnt much from the comment you gave, and I think I need to think about it again.
My reply to your comments as below:

1. I have shifted the signal 13 further apart from the points area, as to make sure that the overlap distance does not included the points I think this shall be the best choices.

2. I agree, so I have moved the signal 12 into the Not Scale potions as to make sure it will not interfere other train movements over the junction.

3. I agree with you, it is not always profitable to implement bi-directional signalling system on the railway network, it’s definitely cost much. So I changed to only using one direction signalling system for station A& B, but bi-directional signalling system for station C as to allows reversal and running around movement of passenger train and freight trains.

4. I agree with you I have re-number the signal on the layout as to leave spare signals for future usage.

5. I am not sure whether my braking distance calculation is suitable or not. As stated from the question that the permitted Passenger speeds is 160km/h. (I’ve taken this figure as my braking distance calculation taking the worst case scenario into calculation), and the braking distance calculated from this is approximately 2km as shown from my calculation. However, the question also says that the required headway for following stopping trains at 120km/h is 6 min, and the non-stopping trains at 120km/h are 3 min. Or shall I taken 120km/h for the braking distance calculation and as the minimum signal spacing?

And when it comes to place signals at station area, we do not place signals 2km apart right? (As for station B there would not have such space available and for station C the station area is less than 2km (from 17.800 km~ 18.450). So I believe the signals in the station area are sometimes not be able to be placed for full service braking distance apart (home & starting signals).

So how should we place the signals at terminal as to suit headway requirement?
Sorry to ask some silly questions as above.

But as I have learnt in the past, when it comes to place signals at terminal. General speaking, we should place home and starting signals at terminals (for entering and leaving the platform area) and they shall be as close as possible to allow quick clearing of signals once train have left the terminal area. Also place junction signals before points area and make sure it’s overlap will not prevent the operation of point area as for the best choice. (But this may be always be possible due to civil constraints etc.)

If took 120km/h for calculation, the braking distance is approximately 1200m.

6. Sure, I have re-signaled the layout for reversal of passenger trains and running round of freight trains. Can you check whether it is appropriate?

I will read through other thread about how to calculate the signal spacing for a stopping train at station area for Question 4, if I have further questions I will ask again.

Attached layout is the revised version.

Thank you for taking time to correct my work

[PJW]

Looking at your revised plan:

I think that some signals still have some route indicators which they no longer need which is a minor thing as far as this question is concerned.

If you read the question it requires that the run round occurs at C with the locomotive running back to A and using the crossover there; you haven't provided a signal (probably a Ground Position Light) to do so.

At C you will also need a shunt route from signal C31 (and therefore a PL) to read up to a Limit of Shunt on the lower line in order to get the loco behind signal C38. You'd need another signal to prevent the usual direction traffic at the time this move up to the LOS is being made.
C38 does not itself require a PL and the loco can be signalled to station A with the signals provided. Then you have a choice;

1. provide a GPL as I explained above so that the loco can use the trailing crossover to get routed tp signal A15,

2. provide a LOS in rear of A13 signal (protected by A3 signal) and a PL aspect and a shunt route reading to that LOS from A16 signal.
Probably 1 is the better option in this case as more economical and also quicker in use.
When the loco gets back to station C then it would need a PL aspect and a call-on move on signal C27 in order to be able to join on to its train again.

Another thing to consider- how does the complete train now return to A?

1. One option is to provide reversible signalling on the upper track on this stretch of line after all.

2. The other option is provide signalling at C which would allow the train to set back far enough to then use the trailing crossover here to regain the correct running line which is signalled for moves towards A.

I do not think that you need the PLs on those signals that you have shown at C. It is perfectly acceptable to use a main route and therefore yellow or green aspect for such light engine movements; indeed it allows the moves to be made faster in the confidence that all tracks are clear etc. You only need a PL and shunting or call-on routes where it would not be possible to clear the normal signal, for example in circumstances in which a track in the line of route is occupied.

However this is all to do with reading the specification and understanding it to ensure your layout facilitates all the operational moves required. The core part of this exercise is headway so I'll next look at your calculations and comment upon those.

Hi PJW:

thanks for your suggestions it gives me another thought about how I should tackle this question.

I have tried to looked through the past IRSE exam papers, and I have modified my approach to the questions as shown from my attached version 1 file. Please check my work to see whether it is correct or not.

I am still having trouble to find methods about how to do the Question 4, but I will try to dig any past of the IRSE exam papers to see whether there is similiar questions or not. I will post my attempt again for you to check and see whether I am on the right track or not.

Basically I will say I will follow the British Practice just to braoden my view on other railway environment.

thanks for taking time to check

[PJW]

Q2.
Should justify your statement why non-stop headway requirement of 3 mins is more onerous than 6 mins stopping headway. Only needs to be brief and consider the additional time penalty that a station stop imposes (i.e. time lost decelerating, time lost dwelling, time lost accelerating back to the through headway speed).

Always round up braking distances; it was sensible to choose a nice round number such as 2000m for a nominal signal spacing. Firstly it is always good to have a bit of margin over the bare minimum, so there is “somewhere to go” is placing a particular signal in a certain position is not possible / practicable / sensible. Secondly it makes your life much easier in exam conditions- quicker and less prone to error.

Good statement of assumptions and clear presentation.

Having shown that headway requirement met by 3 aspects, no need to consider 4 aspects on those grounds. If you end up needing to put 4 aspects for signal positioning on the layout reasons, then self evident that headway requirement will be met so do not even have to mention this.

In this instance I do not believe that you needed to repeat calculations for freight trains; there is only one train per hour. In this example we already know that the passenger service needs signals about 2km apart, so the only stretch of line where the freight headway could be the determining factor is on the line from A to the junction. With a max speed of 100km/h, even if we consider the need to slow over various junctions etc., it must be reasonable to assume that it will average no less than 50km/h, so the headway signals could be very nearly that far apart. In the UK major towns are rarely further apart than that, so obviously it just isn’t going to be the thing that determines how close signals need to be.
Certainly if there had been more freight trains then it could have been a factor. The very important thing of which to be aware is that in reality the freight braking rate is often much less than that of passenger trains; it is not an issue given the numbers given in this question, but otherwise it could be that the freight braking distance from 100km/h might exceed the passenger braking distance from 160km/h and in such circumstances would be the determining factor for the minimum signal spacing for the line.

=====================================================

Q3. You should always show the derivation of the formulae used (other than standard ones such as Newton’s laws of motion), define the various abbreviations / quantities involved and explain (oftn a diagram is helpful). This comment applies actually to Q2; obviously if done there then could just have quoted subsequently.
For example, you have never actually stated that St means Sighting Time etc.

In explanation you said that “For 3 aspect signalling, the distance d equals service braking distance D…..”; this is only true for signals at MINIMUM spacing; they can be more widely spaced than this (often as much as 33% extra, sometimes 50% extra).

The equation for DMAX could do with some further explanation; you need to state that it is the headway time specification Ht which gives the constraint (the fact that it immediately follows the text re the 3 aspect signals at minimum spacing means that the logic of the presentation isn’t easy to follow).

You should also have considered the maximum spacing constraint dictated by the degree of excess braking considered acceptable (as above) in case it is more onerous than that given by headway consideration; in this case it is not the constraint but a statement to that effect should have been included.

Only a minor issue but you should ROUND DOWN the maximum spacing constraint; I’d have been tempted to quote the range as 2000m – 3500m.

==================================================

Q4.
For this part of the question you seem to need to make a choice whether to “start with a clean sheet of paper” or adopt the signal positions as drawn in response to Q1. The way I read it is that you should ignore the proposed position of signal C27 (even though I think you were right to place where you did and worry about the aspect sequence separately). The answer will then be telling you where you COULD place C27 on purely headway and braking grounds, rather than where you SHOULD place C27 when other considerations are taken into account (which is where you have placed it).

Hence I would initially assume signals 2000m on the approach and 2000m beyond the platform starter and work out what headway would be achieved. Assuming that this is less than the required 6 minutes than could determine how much “margin” existed in terms of spare time, then convert this into a distance at the headway speed. This will then tell you by how much the signal spacing could be increased and yet still satisfy the 6 minute constraint. If this figure is greater than 3500m then clearly the stopping headway is less onerous than the non-stop headway; however I would presume that this is not the case and some lower maximum limit would need to apply and this would be the answer to Q4.

In order to calculate the headway between two trains both of which stop at station C, need to work out the time difference between the trains passing the same place. If we choose the place where the front of the train stops at the station platform then it is the easiest to imagine and describe (obviously the time difference at any place is the same).
Start the clock as the train comes to rest.

1. There is then a period of station dwell during which the doors are opened, passengers get out and in, the doors close and the brakes are released prior to the train accelerating. The station dwell time is given as 30 seconds.

2. There is then the time during which the train is leaving the station and travelling sufficiently far that the rear of the train clears the overlap beyond the platform starting signal. Use Newton’s Laws to determine how long the train takes to travel a distance equal to its length L, the overlap length O plus any distance between the front of the train when stationary and the signal (25m is a good assumption). During this time the train will be constantly accelerating.

3. Once this has occurred the signal in rear of the station clears from red to yellow; also at this time the signal further in rear change from yellow to green (actually this all may take several seconds depending whether the track circuits are deliberately slow acting and on the technology used- a relay based system with normal acting tracks may take 0.5 second and therefore really negligible, but an electronic interlocking with slow to pick tracks may well take in excess of 5 seconds so adding this in as a factor is a reasonable assumption.

4. At the minimum headway the following train would by now just be getting to the sighting point of the outer signal; had it been closer then its driver would have seen the restrictive yellow aspect and may have started to brake. The time which has to be calculated is how long it will be before that train then reaches the station and stops in the same place as the earlier train at which time the clock is stopped and will be showing the sum of the times described in 1+2+3+4. The time calculation for 4 is itself composed of several different times, the one to be calculated first is that to stop the train from the headway speed and the associated distance for this to occur. This distance will clearly be much smaller than the train has left to travel and there is a need to state some assumptions re how the deceleration would occur. Given that the outer signal is green then the train has no need to slow, so the length of the sighting distance and the inter-signal spacing will be covered at headway speed. Indeed provided the next signal had become green by the time the train encounters it then it too may be passed at headways speed- even if it is spaced at minimum braking this would be for the maximum permissible speed which is greater than that which the train is travelling. However the driver is unlikely to leave the braking until the very last possible minute, so it may be reasonable to suggest that the braking would start when passing it and continue until the train moving reasonably slowly (say 15m/s) and then the final brake application made to stop in the correct place Hence the difference between the signal spacing and that distance actually needed to stop is calculated; this is then converted into a time based on the 15m/s running. i.e. add
a) the time taken to travel from the sighting point of the outer signal to the inner signal
b) the time to brake to a stand from headway speed
c) the time for the slow speed running within the overall braking activity.

[onestrangeday]

Hi PJW:

Thank you for taking time to review my attempt and your suggestions are very valuable for me for learning. I have attached my revised version for headway calculations of Q2-4 and the layout, please have a look to see whether I am on the track or not.

I would like to ask more questions if it is ok:

1. I think I need to understand the question clearly before I can put on signals on the layout especially to meet the operational requirement.

So my question is On the question it described “Freight - Line A to Line B reversing at Station C, running around via crossovers at Station A and Station C - 1 per night (0100-0600)”.

My interpretation is that the freight train first travel from line A and stop at station C. After that it reverses from the loop in station C and make a cross to the lower line using the crossover at station C and return back to Station A. When it arrives at station A, the freight train makes another cross to the upper line using the crossover at station A.

Or does it depends on how you comprehend the question, I mean the description ?? or may be I pay too much concentration on this ?

2. You have mentioned the following
“You should also have considered the maximum spacing constraint dictated by the degree of excess braking considered acceptable (as above) in case it is more onerous than that given by headway consideration; in this case it is not the constraint but a statement to that effect should have been included.”

Do you mean that when design the signalling layout, in real situation the maximum spacing will be shorter than the theoretical value because of excess braking taken as a major factor ?

3. The result I’ve calculated for Question 4 is differ to what you have presumed (the distance is greater than 3500m), can you check my result ?



Thanks

Q2.
Should justify your statement why non-stop headway requirement of 3 mins is more onerous than 6 mins stopping headway. Only needs to be brief and consider the additional time penalty that a station stop imposes (i.e. time lost decelerating, time lost dwelling, time lost accelerating back to the through headway speed).

Always round up braking distances; it was sensible to choose a nice round number such as 2000m for a nominal signal spacing. Firstly it is always good to have a bit of margin over the bare minimum, so there is “somewhere to go” is placing a particular signal in a certain position is not possible / practicable / sensible. Secondly it makes your life much easier in exam conditions- quicker and less prone to error.

Good statement of assumptions and clear presentation.

Having shown that headway requirement met by 3 aspects, no need to consider 4 aspects on those grounds. If you end up needing to put 4 aspects for signal positioning on the layout reasons, then self evident that headway requirement will be met so do not even have to mention this.

In this instance I do not believe that you needed to repeat calculations for freight trains; there is only one train per hour. In this example we already know that the passenger service needs signals about 2km apart, so the only stretch of line where the freight headway could be the determining factor is on the line from A to the junction. With a max speed of 100km/h, even if we consider the need to slow over various junctions etc., it must be reasonable to assume that it will average no less than 50km/h, so the headway signals could be very nearly that far apart. In the UK major towns are rarely further apart than that, so obviously it just isn’t going to be the thing that determines how close signals need to be.
Certainly if there had been more freight trains then it could have been a factor. The very important thing of which to be aware is that in reality the freight braking rate is often much less than that of passenger trains; it is not an issue given the numbers given in this question, but otherwise it could be that the freight braking distance from 100km/h might exceed the passenger braking distance from 160km/h and in such circumstances would be the determining factor for the minimum signal spacing for the line.

=====================================================

Q3. You should always show the derivation of the formulae used (other than standard ones such as Newton’s laws of motion), define the various abbreviations / quantities involved and explain (oftn a diagram is helpful). This comment applies actually to Q2; obviously if done there then could just have quoted subsequently.
For example, you have never actually stated that St means Sighting Time etc.

In explanation you said that “For 3 aspect signalling, the distance d equals service braking distance D…..”; this is only true for signals at MINIMUM spacing; they can be more widely spaced than this (often as much as 33% extra, sometimes 50% extra).

The equation for DMAX could do with some further explanation; you need to state that it is the headway time specification Ht which gives the constraint (the fact that it immediately follows the text re the 3 aspect signals at minimum spacing means that the logic of the presentation isn’t easy to follow).

You should also have considered the maximum spacing constraint dictated by the degree of excess braking considered acceptable (as above) in case it is more onerous than that given by headway consideration; in this case it is not the constraint but a statement to that effect should have been included.

Only a minor issue but you should ROUND DOWN the maximum spacing constraint; I’d have been tempted to quote the range as 2000m – 3500m.

==================================================

Q4.
For this part of the question you seem to need to make a choice whether to “start with a clean sheet of paper” or adopt the signal positions as drawn in response to Q1. The way I read it is that you should ignore the proposed position of signal C27 (even though I think you were right to place where you did and worry about the aspect sequence separately). The answer will then be telling you where you COULD place C27 on purely headway and braking grounds, rather than where you SHOULD place C27 when other considerations are taken into account (which is where you have placed it).

Hence I would initially assume signals 2000m on the approach and 2000m beyond the platform starter and work out what headway would be achieved. Assuming that this is less than the required 6 minutes than could determine how much “margin” existed in terms of spare time, then convert this into a distance at the headway speed. This will then tell you by how much the signal spacing could be increased and yet still satisfy the 6 minute constraint. If this figure is greater than 3500m then clearly the stopping headway is less onerous than the non-stop headway; however I would presume that this is not the case and some lower maximum limit would need to apply and this would be the answer to Q4.

In order to calculate the headway between two trains both of which stop at station C, need to work out the time difference between the trains passing the same place. If we choose the place where the front of the train stops at the station platform then it is the easiest to imagine and describe (obviously the time difference at any place is the same).
Start the clock as the train comes to rest.

1. There is then a period of station dwell during which the doors are opened, passengers get out and in, the doors close and the brakes are released prior to the train accelerating. The station dwell time is given as 30 seconds.

2. There is then the time during which the train is leaving the station and travelling sufficiently far that the rear of the train clears the overlap beyond the platform starting signal. Use Newton’s Laws to determine how long the train takes to travel a distance equal to its length L, the overlap length O plus any distance between the front of the train when stationary and the signal (25m is a good assumption). During this time the train will be constantly accelerating.

3. Once this has occurred the signal in rear of the station clears from red to yellow; also at this time the signal further in rear change from yellow to green (actually this all may take several seconds depending whether the track circuits are deliberately slow acting and on the technology used- a relay based system with normal acting tracks may take 0.5 second and therefore really negligible, but an electronic interlocking with slow to pick tracks may well take in excess of 5 seconds so adding this in as a factor is a reasonable assumption.

4. At the minimum headway the following train would by now just be getting to the sighting point of the outer signal; had it been closer then its driver would have seen the restrictive yellow aspect and may have started to brake. The time which has to be calculated is how long it will be before that train then reaches the station and stops in the same place as the earlier train at which time the clock is stopped and will be showing the sum of the times described in 1+2+3+4. The time calculation for 4 is itself composed of several different times, the one to be calculated first is that to stop the train from the headway speed and the associated distance for this to occur. This distance will clearly be much smaller than the train has left to travel and there is a need to state some assumptions re how the deceleration would occur. Given that the outer signal is green then the train has no need to slow, so the length of the sighting distance and the inter-signal spacing will be covered at headway speed. Indeed provided the next signal had become green by the time the train encounters it then it too may be passed at headways speed- even if it is spaced at minimum braking this would be for the maximum permissible speed which is greater than that which the train is travelling. However the driver is unlikely to leave the braking until the very last possible minute, so it may be reasonable to suggest that the braking would start when passing it and continue until the train moving reasonably slowly (say 15m/s) and then the final brake application made to stop in the correct place Hence the difference between the signal spacing and that distance actually needed to stop is calculated; this is then converted into a time based on the 15m/s running. i.e. add
a) the time taken to travel from the sighting point of the outer signal to the inner signal
b) the time to brake to a stand from headway speed
c) the time for the slow speed running within the overall braking activity.

[PJW]

I look at the calcs later. In brief:

Layout-
Signals 11 and 13 now only read to one destination- therefore no route indicators.
Signal 16 has 2 routes, so just a pos 4 PLJI for the slower speed route.
Need GPL at the junction at station A so that loco can use the railing crossover. Also signal 27 would need a PL so that loco can reattach to its train (make sure that the overlap of 27 is not going to be occupied by the 400m train tailing back).
28 signal doesn't need a PL. It has only one route so do not need the PLJIs; however there is an argument for giving one PLJI (pos1) for the move across to the correct running line, though since the signal can't be approached I don't think I'd provide it.
31 signal wouldn't have PLJI since the move over the crossover is authorised by the PL not the main aspect.
Don't need signal 33.


1. The freight train is 400m long. The locomotive cannot run around purely at C. It has to leave its train behind at signal 31, itself cross to the LOS and travel to station A on one line and then back on the other in order to couple onto the other end of the wagons. Then somehow the whole train needs to go back to station A so that it then goes the other way at the junction.

2. Yes. In the UK a driver is trained to brake on seeing the yellow. If the next signal is very much more than braking distance then will brake until running slowly and then continue until sees the red. Of course if this becomes the norm then drivers will tend not to brake so hard when seeing a yellow. This can be dangerous if they get accustomed to doing this because when encounter a signal at yellow which is only just at braking, then they may not brake enough and then fail to stop in time when getting to the red signal. Therefore we generally attempt to avoid signals being spaced at more than 133 percent of braking. If headway requirements are low (i.e. few trains per hour), then we use 2 aspect signals, with the red/greens spaced dictating the headway, each having its own yellow/green at braking distance on the approach; it is 3 aspect signalling but no one signal shows more than 2 colours.

3. I'll comment on these later.
My description of stopping headway reflects modern "defensive driving" and if you look in older books the methodology used there would give a better headway (but relied on drivers not driving more cautiously when the signal prior to the station at which they are to stop anyway displays yellow compared to green). This may make quite a difference to the numbers.

Hi PJW:

Thank you for taking time to review my attempt and your suggestions are very valuable for me for learning. I have attached my revised version for headway calculations of Q2-4 and the layout, please have a look to see whether I am on the track or not.

I would like to ask more questions if it is ok:

1. I think I need to understand the question clearly before I can put on signals on the layout especially to meet the operational requirement.

So my question is On the question it described “Freight - Line A to Line B reversing at Station C, running around via crossovers at Station A and Station C - 1 per night (0100-0600)”.

My interpretation is that the freight train first travel from line A and stop at station C. After that it reverses from the loop in station C and make a cross to the lower line using the crossover at station C and return back to Station A. When it arrives at station A, the freight train makes another cross to the upper line using the crossover at station A.

Or does it depends on how you comprehend the question, I mean the description ?? or may be I pay too much concentration on this ?

2. You have mentioned the following
“You should also have considered the maximum spacing constraint dictated by the degree of excess braking considered acceptable (as above) in case it is more onerous than that given by headway consideration; in this case it is not the constraint but a statement to that effect should have been included.”

Do you mean that when design the signalling layout, in real situation the maximum spacing will be shorter than the theoretical value because of excess braking taken as a major factor ?

3. The result I’ve calculated for Question 4 is differ to what you have presumed (the distance is greater than 3500m), can you check my result ?

Thanks