(03-08-2009, 08:01 PM)PJW Wrote: (31-07-2009, 02:47 PM)sidshekhar Wrote: Hello,

I have made an attempt at doing calculations for Module 2 layout paper of 2005. Please view the attachment and provide me with you feedback.

Regards,

Sid Shekhar

It'll be a little time before I get a chance to do this- I am pretty busy re the forthcoming mod2/3 event just at the moment. It may be that someone else will respond; otherwise I'll get around to it eventually.....

Just got back from leave and had a look on the train coming home today.

There is a lot in here to show that you have a good basic understanding but there are several points where you have some flawed logic. You have also made some unexplained assumptions which may be fine if you get things right, but if the examiner cannot understand jumps that you have made which you have not explained, you'll lose out.

Your conversion of speeds to m/s at the beginning is always a good idea, but how many of them did you actually use? You may have wasted some time unnecessarily by converting every one and looking at the order of your table, you missed probably the most important one in this context and added it to the end. I am interested in the translation formula that you used because although most of your conversions are close enough, you have arrived at some interesting numbers. For instance, given a speed of 90km/h, you arrived at the very precise 24.30m/s whereas 90x1000/3600 in fact comes to the very round 25m/s, yet your 33.33m/s for 120km/h is spot on.

You have not explained what b is in your SBD equation. It is obviously the braking rate, but you should define all variables.

You stated that the "recommended" headway is 150s. 150s is a REQUIREMENT.

Why assume a sighting time of 10s? State the practice of the railway you are signalling for and give what their requirement is.

Your sums for the calculation of DGR are sound (using the value of 27m/s vice the actual 27.78m/s) the important correct thing here is that you used the value relating to the quoted headway speed of 100km/h.

You would do well to explain DGR, and the other abbreviations (S, O and L). They may well be familiar to someone form the UK, but where will the marker of your exam paper be from?

Again, the concept of N=DGR/SBD is commonly taught in the UK, but just to state formulae with no explanation and no demonstration of understanding will not score you highly. The statement that because N is 2.45 you will use 3 aspect with spacing 0.5DGR may be true, but you should explain what it means.

You did less well on demonstrating the understanding of the stopping headway. Your approach of breaking it down into sections is a good principle, but you have made a couple of unstated and incorrect assumptions.

1. that in t3 you will have travelled the full distance between the two signals and hence 2. when you start again to accelerate after the stop, the only distance you have to go is the overlap plus the train length. In fact, in what you have called t3, you started braking at the signal and took 54 secs to come to a stand. At a braking rate of 0.5m/s/s from 27.78m/s you will have travelled 729 of the 1361m between the signals. Also, when you have accelerated from rest after your (assumed) 30 sec dwell time, you have taken 39 secs to travel the 383m. You are in fact only travelling at 19m/s at this point, so your following train is still catching you up.

Do not assume that the station stop will coincide with a signal position. Based on the numbers you have used, irrespective of where the stop occurs, it will take 54 secs to stop during which time you will have travelled 729m, 30 s at rest and 54 secs to get back up to speed, again travelling 729m. This means that you have gone 1460m out of your Hd of 3375m. The other 1915m are at Hv (either before or after the deceleration / acceleration) and hence take 71 sec, thus your stopping headway time for one stop is 71+54+54+30=209 sec. This compares with 240 sec requirement so you were right that 3 aspect signalling at 1361m meets the requirement (with some contingency), but you did not show it correctly.

Hope that is all clear. Any questions, please come back.

Peter