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.
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.
(03-11-2011, 04:15 PM)onestrangeday Wrote: 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