2013 Layout

[asrisaku]

Plan sht1- Yes you have understood all items.

That is clear. Hopefully I will not fail to understand the speed requirement.

Plan sht2- Red post-it.
Yes, excepting one very little issue is that the PL symbol should have the right angled corner adjacent to the red aspect and the curved arc to be the further from the track but the orientation of the dots for the lights is correct). The symbol of the PL is always drawn like that, so in the rare case that the signal is placed to the right of the line (e.g. sometimes occurs at platform at station) then the PL is again placed further from the track than the red but maintains the same symbol orientation and therefore it is the curved arc that is closer to the track- as I have depicted for 120 signal.

Ok I will aware of the symbol for PL.

Plan sht2- Green post-it.
Yes 402 as single end. Actually the IRJ may not be necessary and track BG could potentially extend to abut AD.

I frequently forgot the classic mistakes. Thanks a lot.

Sht3- Pink post-it
You are right- when I drew suggestion for 120 it was to illustrate how to draw PL and the SARI and did ot attempt to show the main route indicators, but yes I think PLJI 1 & 4 would be ok as no obvious "straight" route. However I think your original choice of SARI aspect was better- the signal is just for "set-back" and isn't approached at speed. Also if standage is tight the driver will not get a very good view from the cab and the SARI is probably better for close visibility The preferred positioning for SARI is to the side of the aspect above the MARI but yes sometime they are placed above the Green when that is the better option for visibility etc

That is clear.

Sht3- Lower green post-it
Yes except that the two dots should be displayed to the driver as a horizontal pair side by side- on the symbol of course that means that the dots are vertically stacked on the page.

I will try to produce two dots vertically as suggested.

Sht3- Lower green post-it
Yes

Thanks

Sht4-
In 4 aspect signalling there is some flexibility; it is a good idea to have the spacing as even as possible but the middle signal within any group of 3 must obey the 1/3rd :2/3rd rule of the total distance (NB not BD but the actual distance which can be greater) from YY to R. Uneven spacing is a bit of a trap for the driver and also impacts headway so best avoided but you can do it and if eases something else may be the solution.
In this case signal 104 simply has to be at the end of the platform where you have shown and thus there must be a signal to give the YY no less than full BD on its approach.
Hence there is little you can do (but note that could save a few metres by placing at 1980m rather than your conveniently rounded number and 204 is placed at 1140m so is rather more than 0.5BD- why could it not be placed more or less where put is overlap?) and I think what you did was correct - I was attempting
a) to answer your worry that it was too far by saying that it was actually acceptable but
b) also to confirm you were indeed right to be concerned since it was "borderline".

If you did need to put an extra signal closer to the junction (I don't think sensible in this case) then you can do so but ensure that the signal in rear is approach released whenever the signal at the end of the short section is at red. In that way the fact that there isn't adequate braking distance does not matter- it is a bit like the transition from 3 to 4 aspects as you indicated but remember that it is an option as "modified 4 aspect signalling" or the equivalent as "modified 3 aspect signalling" which in other circumstances can be a handy way of signalling a layout with 3 aspects throughout but where there are a couple of junctions too far apart to protect by a single signal but not far enough apart to have the separate signals at braking distance.

Appreciate it the useful information above.

Calculations.
Green post-it.
What I meant was "how many trains are there really to travel over that portion of line according to the timetable?".On a pure Metro when throughput is key, and all trains basically the same then you are right that the tph capacity is the reciprocal of headway and it is used evenly through the clock-face hour. On a mainline railway the headway quoted if the shortest time interval at which it is intended to operate one train following another. It may be that this is quoted say as 2 minutes but actually there are probably only 6 scheduled trains within an hour- the headway that is needed so as not to unduly delay a service is generally nowhere nearly fully exploited. If the actual service is sparse then the "design headway" should match the "timetabled headway requirement", if however a good percentage of the number of theoretically available paths are really utilised then an element of contingency is then needed between the capacity sold by means of the timetable to the train companies and that for which the signalling makes provision. Hence instead of directly comparing the 3 aspect headway against the 4 aspect headway, you should have considered whether the 3 aspect headway was adequate given the specification of the number of trains using the layout on a range of service patterns and speeds.

If I understand well, the station C dominates the headway(bottle neck) because the number of trains per hour is maximum (10 trains per hour by assumption below.)
Passenger btw B and G 2 per hours(via C)
Passenger btw B and G 2 per hours(via C)
Passenger btw A and C 1 per hour(via C)
Passenger btw A and E 1 per hour(via C)
Passenger btw C and B 1 per hour(taking the worst case instead of 1 per day)
Freight btw A and G 1 per hour(via C)
Freight btw B and E 1 per hour(via C)
Freight btw G and A 1 per hour(taking the worst case instead of 1 per week)
Then totally there are 10 trains per hour. Timetable headway shall be 60/10 = 6 mins. However, stopping train and freight train which has speed lower eat up more capacity. 6mins is changed to 3mins for timetable headway.
Refered to 2 mins from design technical headway, this comfortably can achieve the requirement of 3 mins and provide 33% contingency to recover the service.

Red post-it
The explanation should refer to the risk of driver complacency if they find that all the signals in an area are overbraked- this then causes them not to brake very hard when encounter caution aspects, but this becomes dangerous when they happen to encounter a section at bare minimum spacing. One third overbraking is considered reasonable, but greater percentages bring increasing risk and therefore we aim not to exceed 1.33


Route Boxes
My error- I put ticks on invalidly. 303 again is a GPL and therefore does not need approach release.

Could you please check my understanding again?

Thanks again.

Thanks for a lot of good lessons that were pointed out.

[PJW]

o problem. Yes you have understood re the headway- it is more than just adding up the number of trains in the hour but can only make a general approximation re how many timetabled pths are consumed due to the mix of traffic types and hence what you have written is eminently reasonable. Can't afford to waste much time on calculating details, just enough explanation to show you have a firm appreciation of the scenario.

Thanks for a lot of good lessons that were pointed out.

[asrisaku]

May I have comments on Stopping Headway Calculation?

I have studied the model answer and came up with a question why the distance 1st train for overlap and train length is not considered.

Thanks
Arnut

[dorothy.pipet]

Blank layout and question paper FYI