04-10-2012, 10:48 AM
Might be a little late know with the exam on Saturday but wondered if i could get a little bit more feedback on the question as a whole.
The question asks to derive a strike in running at 140km/h with three aspect signalling with minimal delays to the rail traffic.
I approached this by drawing a diagram which showed the crossing the 3 signals in approach and the overlap of the final signal before the crossing. I assume that for minimal delays a train driver would only encounter green aspects.
I am a little unsure of braking distances and signal sighting distances so I assumed 800m to stop from 140km/h and 200m to see a signal. This meant that the two signals closest to the crossing were 800m apart. This plus the 180m overlap plus an extra 10m as the overlap wouldn't want to be in the crossing area means the final signal must display a green aspect when the train is 1190m from the crossing.
The crossing sequence should show amber for 3 secs before red lights for 6s before the entrance barriers lower. Then 8s for the barriers to lower and the signaller to confirm the crossing was clear before the exit barriers lower which shall take a further 6seconds. This totals 23secs. 23secs at 140km/h is 894m so the strike-in should be 2084m from the crossing.
i) I don't think 4 aspect would affect this distance as the driver is only seeing green aspects but the three signals closest to the crossing will be 800m apart (2x400m) so the strike in is the same
ii) this may save a couple of seconds @ 140km/h is 78m closer to the crossing.
iii) the sighting distance will no longer be required so 200m closer to the crossing.
On the final part I was really unsure so if anyone has anything they can suggest on this I would appreciate it. The only thing I know about in this respect are level crossing predictor technology that uses the change in impedance to calculate the speed of the train and whether it is deccelarating. This could be used with a treadle for stopping trains but i am not sure of the traditional meathods.
Thanks for reading
The question asks to derive a strike in running at 140km/h with three aspect signalling with minimal delays to the rail traffic.
I approached this by drawing a diagram which showed the crossing the 3 signals in approach and the overlap of the final signal before the crossing. I assume that for minimal delays a train driver would only encounter green aspects.
I am a little unsure of braking distances and signal sighting distances so I assumed 800m to stop from 140km/h and 200m to see a signal. This meant that the two signals closest to the crossing were 800m apart. This plus the 180m overlap plus an extra 10m as the overlap wouldn't want to be in the crossing area means the final signal must display a green aspect when the train is 1190m from the crossing.
The crossing sequence should show amber for 3 secs before red lights for 6s before the entrance barriers lower. Then 8s for the barriers to lower and the signaller to confirm the crossing was clear before the exit barriers lower which shall take a further 6seconds. This totals 23secs. 23secs at 140km/h is 894m so the strike-in should be 2084m from the crossing.
i) I don't think 4 aspect would affect this distance as the driver is only seeing green aspects but the three signals closest to the crossing will be 800m apart (2x400m) so the strike in is the same
ii) this may save a couple of seconds @ 140km/h is 78m closer to the crossing.
iii) the sighting distance will no longer be required so 200m closer to the crossing.
On the final part I was really unsure so if anyone has anything they can suggest on this I would appreciate it. The only thing I know about in this respect are level crossing predictor technology that uses the change in impedance to calculate the speed of the train and whether it is deccelarating. This could be used with a treadle for stopping trains but i am not sure of the traditional meathods.
Thanks for reading