2008 Module 2 Layout Calculation Attempt

[Peter]

Hi all,
Could u plz take a look of the calculations and comment.
Also can someone clarify whether contingency in headway time be considered or not while calculating the headway.

Thanks

Comments as they come up in no particular order of importance.

You have calculated the sighting using the headway speed. You should use the linespeed for this as the reduced headway speed is recognising that the trains may not be running at the max. However, sighting, like braking calcs, must use the worst case.

Albeit arithmetically correct, your conversion factor for kilometres per hour to ms-1 uses the scale of 5/18, rather than 1000/3600. You should probably explain (at least once), your shorthand.

You have attempted an explanation of the N=DGR/BD formula but I think this is sightly incomplete. Personally, I would not rely on using this and trying to explain it. Far easier to write a simple explanation of why the numbers you have calculated mean that 2, 3 or 4 are appropriate or not appropriate from first principles. Eg HD = x and spacing for y aspect signalling are compatible or incompatible. You have effectively shown that anyway by the calculation of the headway time for 4 aspect. If you repeat this for three aspect, you will see that it does not quite fit, therefore you have the justification for what you have selected.

You can use the N formula for your own satisfaction to see where you start justifying your decision, but I'd avoid it.

One minor point in the DGR formula - You have stated that if N < 1.5 then the calculation is wrong. This is not necessarily so, it normally means that you cannot achieve the headway with the braking characteristics even with 4 aspect signalling.

On the question of contingency, you can either add it into the require Ht ( eg say achieve better than 120 s so that if things go wrong you have some to spare) or work out using it with no contingency and then say that you will adjust the distance by a factor to allow for contingency. There is no right or wrong way to do it, you just need to make sure that you note that it should be included and make reasonable judgements.

Will have a look at th stopping element a bit later for you.

Peter