Aspect Sequence exercise

[PJW]

I'll perhaps annotate your examples when I get a chance, but you need to show a transition from one aspect (say red) to a better aspect occurring and against this show the condition which triggers this change. These are shown as vertical lines (and isanother reason for drawing the sequence lines horizontal and diagonal ather than vertical)- to distinguish more easily my preference is to show dashed. You will find several examples of this in attachments in other posts in this topic area.

Aspect sequence only appicable to lineside signalling and is of course rather different for a speed signalling system than the route signalling system (which itself is, when combined with the driver's "route knowledge" effectively a distance-to-go system) used in the UK.

Aspect sequence if all about how the necessary advanced warning is given to the driver when passing one signal as to the aspect displayed aat the subsequent one for situations in which unable to stop within the distance for which a signal is readable. On tramways and certain metros the speed is low enough, the train is light enough and has good enough brakes so it can be practicable just for a driver to see a red and stiop at it, in a similar way to driving a car. In that environment, o aspect sequence is necessary.

Hi PJW:

Thanks for your suggestion. I looked through the past model answer for aspect sequence, as you have already said they use either vertical or horizontal lines to show the aspect sequence. As for your experience, do they still use aspect sequence for the modern railway signalling system (such as Metro, High Speed Rail as most of its system uses distance to go principle) ?

One question to ask, you have mentioned about
‘You have not shown any approach release. Where the speeds of a diverging route is different from the straight route,’
if I want to show that on the aspect sequence, do I write such as”## OCC” , ##=name of the track circuit , OCC=approach release

Just a quick initial glance of the presentation of sequence on screen without checking to layouts suggests are on right lines; nothing too awful such as a Green reading up to a Red.
Two things that immediately strike-
1. You have not shown any approach release. Where the speeds of a diverging route is different from the straight route, then the signal must be held at red (or in some specific cases at yellow) until the train has got sufficiently close so that driver can see both the route indication and the actua colour of the signal aspect- certainly needs to have received a caution aspect on the signal prior.
2. An aspect sequence chart is easier to read if you avoid depicting the lines completely vertically, but slope at a slight angle. Much clearer that chart reads right to left or left to right; also twhat is a "convergence" from two parallel signals in rear or what is a spreading out to reflect multiple routes from a junction signal. In particular on oe diagram you have joined both categories of the above in the same vertical line. It isn't actually incorrect but since the whole purpose of such a diagram is to give a pictorial readily assimilated depiction of the sequence, it rather loses the whole point if need to study hard to work out what is happening. In reality no real problem on such a simple layout, but as a matter of principle for application to more complicated sites then it is an important consideration. [Note that you will find many sequence charts on modern prjects do use the vertical lines- this I think happens because it is easier for the designer using CAD and saves a little space, but as a user it is definitely unhelpful, so much so that the diagrams rarely get used and everyone refers to the Control Tables- the easy to understand presentation showing the "whole picture" just fails to achieve its end and in my opinion we might as well not have them!]

Hi Signalling Professional:

This is the first time I have tried an exercise for aspect sequence (single line and double line layout which I have done earlier) . can someone check my work ? and I would like see whether I am on the right track or not.



thanks