another try at double line layout

[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