07-03-2014, 08:41 PM
My knowledge/experience is all UK mainline practice; in the exam you should apply your own knowledge/experience and state which railway that is for.
#2a With respect to the down branch, the braking distance is 400m and the next signal is 5km away. When we're using 3 aspect signals the minimum spacing is braking distance apart. There is also a maximum to avoid driver complacency. This is when a driver knows the signals are further apart and delays applying the brakes, but delays too long so cannot stop at the signal. We often use 1.33 x braking distance for this maximum. Consequently the signal spacing on the branch is too long for 3 aspect signals: the branch must use 2 aspect signals, thus, Signal 31 would be a red/green 2 aspect signal.
#2b Looking at the braking distances on the down main, I think most are within the range for 3 aspect signalling, there is just one that is too short. The examiners want to see how you cope with that complexity, and there is more than one "correct" method.
#3 As far as I can see you have not provided a route into the sidings. Where would you approach them from - signal 15 or 23 or both? What type of aspect - perhaps a shunt route so a subsidiary aspect?
#4 Which leads me to realise that you have illustrated a subsidiary aspect on signal 13 but not explained it.
#2a With respect to the down branch, the braking distance is 400m and the next signal is 5km away. When we're using 3 aspect signals the minimum spacing is braking distance apart. There is also a maximum to avoid driver complacency. This is when a driver knows the signals are further apart and delays applying the brakes, but delays too long so cannot stop at the signal. We often use 1.33 x braking distance for this maximum. Consequently the signal spacing on the branch is too long for 3 aspect signals: the branch must use 2 aspect signals, thus, Signal 31 would be a red/green 2 aspect signal.
#2b Looking at the braking distances on the down main, I think most are within the range for 3 aspect signalling, there is just one that is too short. The examiners want to see how you cope with that complexity, and there is more than one "correct" method.
#3 As far as I can see you have not provided a route into the sidings. Where would you approach them from - signal 15 or 23 or both? What type of aspect - perhaps a shunt route so a subsidiary aspect?
#4 Which leads me to realise that you have illustrated a subsidiary aspect on signal 13 but not explained it.