2009 Main Line Layout

[Peter]

I have been practising attempting past papers and have the following questions arising from attempting the 2009 Main Line layout:

1.Using distance from G to R calculations at service speed of 120km/h; I determined that 3 aspect at 140km/h permissible speed would be suitable.However,on signalling the layout;I noticed tight spacing generally.Especially between Station B and Junction D and out of the tunnel to the junction after the single line along the down branch.When I tried 4 aspect;the spacings seemed to suit all the layout generally well.Is there a way my calculations could have forewarned me as I would have run into into serious time constraints in the actual exam having started using 3 aspect?

I have not got the layout with me at the moment, but from what you have said, I suspect you are overlooking something - just because 3 aspect will meet the headway requirements, this does not mean that you would not use some four aspect signalling where the need arises. If the spacing constraints in the station area make this inevitable, use four aspect in this area and sort out the transition to and from the 3 aspect signalling that meets the requirements on the open line.

I'll try to get to look at the other questions when I get a chance to look at the layout.

Peter