2008 mainline layout attempt

[steve]

Well I went for a mostly 3 aspect design.

I did consider OTW on the single track branch but thought that with the mixed bi-di traffic and levels of use, and more importantly the 1.5 hours exam time, I would stretch 3 aspects out along there too. It did seem to fit in quite well with the stations and junctions, though may be a bit pricey for some peoples taste.

Any advance on that...? 4 aspect, ERTMS solutions...

[PJW]

Well I went for a mostly 3 aspect design.

I did consider OTW on the single track branch but thought that with the mixed bi-di traffic and levels of use, and more importantly the 1.5 hours exam time, I would stretch 3 aspects out along there too. It did seem to fit in quite well with the stations and junctions, though may be a bit pricey for some peoples taste.

Any advance on that...? 4 aspect, ERTMS solutions...

I wouldn't recommend an ERTMS solution......I hasten to say that is because I understand that there is freight specified to use the branch and that would need a large number of locomotives to be fitted nationally to ensure that any train that may require to use the line could do so.

PJW

[Artur]

4 aspect signalling seemed to me a natural choice for main lines due to high speed and short headway. However, if you wanted to apply 20% contingency onto required headway then you would end up with... 4 aspect being not sufficient to deliver the headway... WOW! Where to go from there???

The easiest way was to reduce the contingency which appeared to be not ideal but the only way out. Was there anything ealse you could do?

Artur

[PJW]

4 aspect signalling seemed to me a natural choice for main lines due to high speed and short headway. However, if you wanted to apply 20% contingency onto required headway then you would end up with... 4 aspect being not sufficient to deliver the headway... WOW! Where to go from there???

The easiest way was to reduce the contingency which appeared to be not ideal but the only way out. Was there anything ealse you could do?

Artur

Mmmmmm!
I haven't seen the question paper but one person tells me that 3 aspects are sufficient, yet another that even 4 aspects barely achieve required headway. I don't know what the truth is, but I detect inconsistency, so it looks like ione of you got your numbers wrong ......

PJW

[Artur]

permitted speed on main lines 160km/h
Non-stoppting headway 2min at 140km/h

Stopping headway 4min (Fast following stopping) at 140km/h

What do you suggest Peter?

[nthomso3]

I agree with Artur. I had to reduce my contingency to get a decent margin for signal spacing.

[steve]

Perhaps I should mention that I didn't gegt very far with the stopping headway calcs, and just cracked on with the layout, I was going to get back to the calcs but ran out of time. I get the feeling I might have to resit!

[Peter]

I've done some jottings that are in the attachment here and I tend to agree that 4 aspect on the main line would be necessary and even at minimum braking, you only deliver 100s so any variation does eat into your contingency.

For stopping calcs, I've employed the "how much time does a stop add into your front train" approach. ie take your NS headway and add time for deceleration, acceleration and dwell and see what you get, using line speed for all of this (assuming your fast is bearing down on you like that) but then converting the distances to time using headway speed to give a worst case (discuss!) you get 230s.

I've not looked at the branch or the freight. I must admit, if the numbers were that tight when I was doing it, there is not much you can consider if the freight does not meet it!


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[PJW]

I've done some jottings that are in the attachment here and I tend to agree that 4 aspect on the main line would be necessary and even at minimum braking, you only deliver 100s so any variation does eat into your contingency.

For stopping calcs, I've employed the "how much time does a stop add into your front train" approach. ie take your NS headway and add time for deceleration, acceleration and dwell and see what you get, using line speed for all of this (assuming your fast is bearing down on you like that) but then converting the distances to time using headway speed to give a worst case (discuss!) you get 230s.

I was working on the 2009 Study Pack over the weekend and am putting ETCS information into it and may even attempt the 2008 layout as Level 2 withou signals.
I started by attempting to address the braking and headway calcs; I don't know what the examiners would expect (I suspect they have no idea either) so I have made a stab that I'll probably ask them how they'd rate. Problem is you either say "Not applicable to ETCS" that sounds like a get-out and isn't really true anyway (so how could they award marks) or you go into a lot that they may give no credit for (the precise question as asked is not sensible for ETCS, the constraints are not to do with braking and most of the constraints are not associated with "Signalling the Layout"......)

I'd appreciate comments on my approach (EVEN IF YOU DON'T KNOW ETCS THEN YOU CAN FOLLOW MY REASON, ENSURE LOGIC WATERTIGHT / EXPLAINED AND CHECK MY MATHS). I followed a similar approach to Peter re the fast train catching up the stopping train, but felt that the question meant that even the non-stop are only scheduled to run at 140km/h not the 160km/h that Peter assumed.

[Jerry1237]

Can I ask a naive question. Why do we take de-acceleration of a train to be 0.5m/s/s?