22-09-2012, 12:31 PM
Hi PJW,
Thanks for your very helpful and prompt reply. I can see that what I wrote re: freight trains effectively treating a double yellow as a green is indeed politically incorrect nowadays. Very true
Just to confirm though, at the start of this thread, Reuben's suggested solution stated in the assumptions:
Maximum permitted distance from caution to red = 1.5 * minimum figure
If 3 aspect signalling is used for mixed traffic in the 2009 module 2 case, the distance from caution to red would be 2x the minimum figure for freight trains. Is this OK?
I forget exactly what the old O.S. Nock green IRSE textbook said about having a maximum of 1.5 times the braking distance. Is the main issue that the headway would be impacted if the 1.5 factor is exceeded (mind you, freight headway isn't an issue on this exam)? Or is there a safety issue eg. drivers running on a yellow aspect may "forget" (!) they are approaching a red, as the red is so far from the yellow? Or to say it another way, does having an excessive distance between a caution and a red breed train handling complacency?
I guess in summary, can you confirm Reuben's assumption is valid? If so, is it a safety issue and/or a headway issue or something else?
Also, if you don't mind some very basic questions while I'm at it:
a) I note that the exam question says to define all routes, however, Reuben's solution only includes route boxes for junction signals. Is this because not all routes need defining, or because of a UK practice I'm not aware of, or because the other routes are simple and so have been omitted to save time?
b) Also, please confirm, we don't need to show train protection for Main Line layouts, assuming the question doesn't ask for this. I only ask because Reuben's drawing shows some effort applied to include train protection, plus you mention previously a general AWS/TPWS note should be applied (as well as a specific note about the buffer stop and fixed red). Will this attract any marks, since the question doesn't explicitly ask for this?
Thanks so much,
Robbie
Thanks for your very helpful and prompt reply. I can see that what I wrote re: freight trains effectively treating a double yellow as a green is indeed politically incorrect nowadays. Very true
Just to confirm though, at the start of this thread, Reuben's suggested solution stated in the assumptions:
Maximum permitted distance from caution to red = 1.5 * minimum figure
If 3 aspect signalling is used for mixed traffic in the 2009 module 2 case, the distance from caution to red would be 2x the minimum figure for freight trains. Is this OK?
I forget exactly what the old O.S. Nock green IRSE textbook said about having a maximum of 1.5 times the braking distance. Is the main issue that the headway would be impacted if the 1.5 factor is exceeded (mind you, freight headway isn't an issue on this exam)? Or is there a safety issue eg. drivers running on a yellow aspect may "forget" (!) they are approaching a red, as the red is so far from the yellow? Or to say it another way, does having an excessive distance between a caution and a red breed train handling complacency?
I guess in summary, can you confirm Reuben's assumption is valid? If so, is it a safety issue and/or a headway issue or something else?
Also, if you don't mind some very basic questions while I'm at it:
a) I note that the exam question says to define all routes, however, Reuben's solution only includes route boxes for junction signals. Is this because not all routes need defining, or because of a UK practice I'm not aware of, or because the other routes are simple and so have been omitted to save time?
b) Also, please confirm, we don't need to show train protection for Main Line layouts, assuming the question doesn't ask for this. I only ask because Reuben's drawing shows some effort applied to include train protection, plus you mention previously a general AWS/TPWS note should be applied (as well as a specific note about the buffer stop and fixed red). Will this attract any marks, since the question doesn't explicitly ask for this?
Thanks so much,
Robbie