2005 Module 2 Layout Calculations

[kiran218]

Dear PJW,

If contingency is provided for headway is 10% and headway time is 150sec. Practical headway time we have to take 150/1.1=136 or 150-10%=135 which is we have to fallow in the exams. what is the difference between two.

with regards,
kirankumar

Some allowance for contingency is usually sensible unless it is evident that the specified headway is very much less than would ever be needed to make some allowance for perturbation in a timetable.

The more the train service approaches that of a metro to be used to maximum capacity for an extended period of time, the greater the allowance which should be made.

Where there are a few spasmodic trains within the hour then no significant margin between the "timetabled need" and the "signalling design" is needed- even so it is sensible to have a small allowance to give a small margin. If you were the signalling contractor and designed signalling precisely to deliver say 180second headway as per the specification, yet (because of slight rounding errors and slightly false assumptions re how trains are driven etc) it turns out that it only delivers 182secs, then you have a big problem. The railway company would state you had failed to meet an essential criteria; to modify the signalling would be extremely expensive and take a lot of time and effort. If only the design had been for 175sec instead, then if it turned out that it really only delivered 178sec there would have been no issus since still within the threshold. The marginal cost of slight exra capacity at the initial stage would have been quite trivial.

The whole point is that it is a judgement call, depending on all the circumstances; for IRSE exam I would not be overly concerned whether put a 10 second contingency or any reasonable percentage say from 2 - 20 per cent. Understand WHY we put a margin and the factors that determine what might be appropriate; don't worry re the ABSOLUTE VALUE in any particular circumstance!

Hi NJK,

1o percent of contigency is required for headway time. Under what conditions we have to fallow this?

With Regards,
KiranKumar

Dear Members,

I have attempted module 2 2005 layout calculation. Kindly review it and give your comments for my further enhancement.

Thanks in advance.

Regards,
NJK