(03-10-2010, 05:48 PM)PJW Wrote:(03-10-2010, 05:28 PM)Alex Wrote: For non stopping which was for trains every 10 minutes, two aspect with distant signals was OK but the determinant was really the stopping.
No contingency for headway required - so even with stopping three aspect will do the job although as usual four aspect would be more suitable given the numerous junctions there. Headway required was 3.5 mins.
I'd like to see the question paper before comment too much on this.
Refering to the layout Peter has posted (not seen the actually question paper yet) it is clear to be that the majority of the traffic terminates at station G; on this stretch as Alex says it is the "Fast following stopping" consideration that dominates. I haven't done the sums but doesn't seem too onerous so can well believe that 3 aspects adequate to provide that headway.
Beyond the station where there are only two trains an hour then the quoted 10 minute headway would have plenty of contingency recovery already built into it so the section signals could be about 15 miles apart and still provide the headway- in reality it is probable that they would often be needed more frequently to protect junctions, level crossings etc; anything other than stop & distant signalling in this portion would be excessive.
Obviously there would need to be very little signalling on the freight single line branch- it could perhaps be token (or even train staff) worked with trains stopping to pick up / set down at station C.
So Amit, yes at first glance everything was right with the paper. The thing that you seem to have overlooked is that the only stated NON-STOP requirement was for the line beyond G to H. Obviously the same trains also use A to G, but because this was not the key factor here you should have signalled according to the FAST FOLLOWING STOPPING requirement.
PJW