2004 Headway Calcs

[PJW]

Only set it up like this so that we could have multiple people doing the same thing working to a common deadline and once it had expired then making all attempts visible to review together. Not really working out like that at the moment, so have made visible- will look at over the weekend once I've sorted myself out after the weeks holiday!

Yes, the idea is a good one. Not quite sure if the settings are right - if you have made it visible, it still does not show up. I'll try to have a look when I'm not being badgered to get off the computer.....

It has worked before OK; I think that it could have been operator error by me. I certainly had the options in Admin CP but may have not selected the right one before actioning. They have disappeared from the "awaiting moderation" but the good news is that they were not entirely deleted so I have downloaded and post here with my annotations.
I take that back- seems to have been some delay but the attachments have now magically appeared without me doing anything- but perhaps the other Peter did something

Basically the stopping calculations were fine and reasonably well explained. One of the examiners is particularly adverse to the DGR method, so you do need to be especially careful with your explanations if using this. I would advise use of a diagram annotated with the abbrievations that you are going to use and just a few more words of explanation (as I have shown in blue)- it was towards the end when you started to use abbrieviations that (although I grant pretty obvious) you hadn't actually defined.
I used Red text to indicate the "compulsory" rather than "advisable" comments / corrections.

The stopping headway wasn't so good; the elements included are basically sound, but the answer stopped short of proving that 3 aspects at minimum (or indeed some greater spacing) would be adequate to deliver required headway. You didn't state your assumptions- such as that it was "stopping following stopping" that you were being asked to calculate rather than "fast following stopping"- either of which I'd regard as plausible given the question set.

Its main defect is that it did not relate the times t1-t4 calculated to the actual stopping headway which would be achieved. A subsidiary defect is that the t4 calculated did not match the t4 of the diagram provided.
Hence I'd give you some marks for being able to use Newton;'s laws of motion and for being vaguely on the right lines; however your answer does NOT convince me that you understand the impact that the first stopping train would be having on the aspect sequence behind it and therefore on the manner in which the drver of the following train (not even mentioned in your answer to either part of the question!!) would be driving. The fact that the t4's don't match, suggests that you have mix-and-matched bits from various sources but not properly integrated them in your brain and hence don't fully understand the significance of what you are doing.
All the bits are good; but they do need to be bolted together correctly!
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As an overview of what you are trying to do:
1) Initial condition; two trains following each other at constant speed (it not actually stated whether this is the max 120km/h or some lower timetabled speed, so you should explicitly state your assumption- you chose 100km/hr which is perfectly reasonable, but did you really think enough about this and choose for the right reason)
2) Train 1 slows down to stop at station; Train 2 catches it up slowly at first and then quite quickly once first is stopped.
3) Unless Train 1 has cleared the overlap of the station starter before Train 2 reaches the sighting point of the second 3-aspect signal in rear, then it will receive a caution aspect at it. Question is whether this will affect how Train 2 is driven- what do you think?
4) Unless Train 1 has cleared the overlap of the signal beyond the station starter by the time that Train 2 reaches the signal reading into the station, then it will receive a caution aspect at it. Question is whether this will affect how Train 2 is driven- what do you think?
5) Unless Train 1 has cleared the overlap of the second signal beyond the station starter by the time that Train 2 is ready to depart from the station, then it will receive a caution aspect at the station starter. Question is whether this will affect how Train 2 is driven- what do you think?

Remember that "headway" is all about one train NOT impacting on another. Not a perfect analogy by any means, but perhaps easier to think about; a stream of traffic progressing smoothly on a motorway. Another similar motorway merges; if traffic on both is sufficiently light then although the resultant traffic is heavier than it was, it carries on flowing quite freely and no one really minds or notices. However as the level of traffic on both gradually increases later on in the day, what often happens is that a capacity limit is reached and then average speeds drop- indeed there can be quite a pronounced tipping point and it can get very slow stop-start with big build ups for many miles.
Traffic jams on the railway tend to be far less visible (until we get ETCS L3 or at least virtual blocks) as instead of getting vehicles bumper to bumper we keep them a full block section apart, but they happen none-the-less.
Stopping headway has no clear analogy with roads since it is normally so easy to overtake and relatively quick to brake and accelerate. I suppose "Fast following Stopping" could be a bit like a car driver who would catch up a bus on a stretch of lightly used narrow road where overtaking isn't an option; the calculation would then be how much head-start would the bus need over length x with y bus stops for it to have cleared the narrow section before a car which travels faster and without any requirement to stop just reaches it at the first overtaking opportunity.

So taking an overview of your answers I'd say all the "mechanics" are ok but you largely failed to demonstrate to me that you had grasped the "big picture" of what the activity is all about and why it is such an important part of signalling the layout- i.e. the throughput of traffic. Hence suggest you need to do more work in that regard to be able to gain the marks on offer.

See also
my response to Alex