No such thing as a silly question; actually you are asking all the right ones. This is exactly what the website is for.
1-4. Yes you have clearly understood what I was explaining.
5. Not yet myself looked at calculations. Hopefully later today.
However yes in a station area there is often a need to have signals closer than would be permitted by having 3 aspect signals at the braking distance apart, particularly as in this case when it is so long.
Therefore need to something a bit special, which could be:
a) signal as a "mechanical area" with one distant signal for all the signals for one direction at that site- the various "homes" and "starters" would be red/green and the only separation which needs to be at braking is from the distant to the first of them,
b) signal with 3 aspect MAS but impose approach release conditions "modified 3 aspect sequence" to ensure that when signals too close that the train speed has already been brought down low enough such that there is then braking at that speed,
c) have an area of 4 aspect signalling
d) reduce the permissible speed in the area (which is obviously the solution which best fits terminal stations).
I was slightly alluding to this scenario as a very subtle hint in my earlier reply. I think we need to study the calculations first, then return to this topic.
Not all railways would adopt all of the above solutions a-d; hence this raises the question:
"which railway's practices are you attempting to follow"?
This I accept may be a hard one for you to answer given that your experience isn't with such signalling at all. If you are using IRSE publications then generally these reflect UK practice, but perhaps from your geographic location there is influence from Australia? Much is similar but there are differences and indeed from one Australian state to another. I am no expert on this but I have been given access to some of their standards and have a few contacts from whom I could seek advice if this were the case. Otherwise if you are just trying to learn "a version" then probably best to stick generally to the UK approach. Problem is that when you are learning it can be unnecessarily confusing to be introduced to many variants before one is clearly established in the mind.
1-4. Yes you have clearly understood what I was explaining.
5. Not yet myself looked at calculations. Hopefully later today.
However yes in a station area there is often a need to have signals closer than would be permitted by having 3 aspect signals at the braking distance apart, particularly as in this case when it is so long.
Therefore need to something a bit special, which could be:
a) signal as a "mechanical area" with one distant signal for all the signals for one direction at that site- the various "homes" and "starters" would be red/green and the only separation which needs to be at braking is from the distant to the first of them,
b) signal with 3 aspect MAS but impose approach release conditions "modified 3 aspect sequence" to ensure that when signals too close that the train speed has already been brought down low enough such that there is then braking at that speed,
c) have an area of 4 aspect signalling
d) reduce the permissible speed in the area (which is obviously the solution which best fits terminal stations).
I was slightly alluding to this scenario as a very subtle hint in my earlier reply. I think we need to study the calculations first, then return to this topic.
Not all railways would adopt all of the above solutions a-d; hence this raises the question:
"which railway's practices are you attempting to follow"?
This I accept may be a hard one for you to answer given that your experience isn't with such signalling at all. If you are using IRSE publications then generally these reflect UK practice, but perhaps from your geographic location there is influence from Australia? Much is similar but there are differences and indeed from one Australian state to another. I am no expert on this but I have been given access to some of their standards and have a few contacts from whom I could seek advice if this were the case. Otherwise if you are just trying to learn "a version" then probably best to stick generally to the UK approach. Problem is that when you are learning it can be unnecessarily confusing to be introduced to many variants before one is clearly established in the mind.
(03-11-2011, 05:40 AM)onestrangeday Wrote: Hi PJW:
Thanks for taking time to review my work. I have learnt much from the comment you gave, and I think I need to think about it again.
My reply to your comments as below:
1. I have shifted the signal 13 further apart from the points area, as to make sure that the overlap distance does not included the points I think this shall be the best choices.
2. I agree, so I have moved the signal 12 into the Not Scale potions as to make sure it will not interfere other train movements over the junction.
3. I agree with you, it is not always profitable to implement bi-directional signalling system on the railway network, it’s definitely cost much. So I changed to only using one direction signalling system for station A& B, but bi-directional signalling system for station C as to allows reversal and running around movement of passenger train and freight trains.
4. I agree with you I have re-number the signal on the layout as to leave spare signals for future usage.
5. I am not sure whether my braking distance calculation is suitable or not. As stated from the question that the permitted Passenger speeds is 160km/h. (I’ve taken this figure as my braking distance calculation taking the worst case scenario into calculation), and the braking distance calculated from this is approximately 2km as shown from my calculation. However, the question also says that the required headway for following stopping trains at 120km/h is 6 min, and the non-stopping trains at 120km/h are 3 min. Or shall I taken 120km/h for the braking distance calculation and as the minimum signal spacing?
And when it comes to place signals at station area, we do not place signals 2km apart right? (As for station B there would not have such space available and for station C the station area is less than 2km (from 17.800 km~ 18.450). So I believe the signals in the station area are sometimes not be able to be placed for full service braking distance apart (home & starting signals).
So how should we place the signals at terminal as to suit headway requirement?
Sorry to ask some silly questions as above.
But as I have learnt in the past, when it comes to place signals at terminal. General speaking, we should place home and starting signals at terminals (for entering and leaving the platform area) and they shall be as close as possible to allow quick clearing of signals once train have left the terminal area. Also place junction signals before points area and make sure it’s overlap will not prevent the operation of point area as for the best choice. (But this may be always be possible due to civil constraints etc.)
If took 120km/h for calculation, the braking distance is approximately 1200m.
6. Sure, I have re-signaled the layout for reversal of passenger trains and running round of freight trains. Can you check whether it is appropriate?
I will read through other thread about how to calculate the signal spacing for a stopping train at station area for Question 4, if I have further questions I will ask again.
Attached layout is the revised version.
Thank you for taking time to correct my work
PJW