Virtual Study Group

[PJW]

Sir, Contigency is generally to required to recover the service perturbations and the contigency will acts as a buffer. Contigency of 25% is taken in order to design the signaling which gives greater capacity.

Sir, Is this value of contigency depends upon the timetable i.e., no.of services needed per hour?

Yes look at how many trains per hour as well as just the closest pair of trains requiring to be timetabled in order to determine a suitable level of contingency.
If there is a need for a train every 5 minutes, 12 trains per hour then there must be a decent level of contingency, otherwise if one train is delayed for just a couple of minutes, then many subsequent trains will be delayed. Designing signalling with plenty of contingency might mean for example designing to achieve a headway of 4 minutes. This would mean that the 2nd train would only be delayed by 1 minute and the third could be on time; if less contingency provided with the signalling achieving 4.5 minutes, then the 2nd train would be delayed by 90s, the 3rd by 60s, the 4th by 30s and it would be the 4th before the timetable could be recovered fully.

Conversely if there is an ocasional need for a train to follow another 5 minutes apart but then there is no other train for half an hour, then don't really need any contingency at all, since there would be no knock-on delay to a significant number of trains anyway. Train 1 would delay train 2 by the same amount but then there is plenty of spare time before train 3 is in the area.

In the three aspect signaling i think the maximum distance is to compare with the SBD+33% to determine the over braking. In case of four aspect it is SBD+33%/2.

Yes, you are right; however you need to be careful in your explanation and presentation that you do not confuse spacing between adjacent signals and spacing between alternate signals in the 4 aspect case.

If overbraking exists in a given headway my idea is it can be reduced by over providing MAS continuously with max. signal spacing.

Yes, again I believe you correctly understand. However I suggest you do not use the phrase "over providing MAS" as it is liable to be misunderstood; it would be better to say "Provision of MAS with the greatest signal spacing being limited by considerations of overbraking rather than the need to provide the required headway"