Sorry for delay; yes looks much better to me. Sensible degree of rounding etc.
A few small points
1. I don't know whether it was luck or skill that placed signal 29 at 300m from the point and this happened to turn out to be the distance needed to brake to turnout speed! Actually the speed restriction through the points applies to the curved path through the turnout and its approach (as not possible to cant it appropriately for the radius of curvature because of the need to join smoothly with the straight line) and thus in reality would apply at latest say 50m prior to the switch tips, but that is just a quibble.
2. The calculations are not exactly consistent with the demarcation line drawn separating T2/T3; it was a good presentation to show what you were going to calculate, but for the benefit of anyone else looking to tie the numbers with the diagram it is worth stating that this showed your initial assumption which was actually later refined when the numbers were produced, since the braking to a stand would actually not be necessary until well into the platform.
3. As I see it, the datum for the commencement of the platform is at 400m and you have decided to stop the 120m train centrally within it and thus have a 15m allowance at each end. Surely then you have the RH end of the train at 385m and the LH at 265m. When calculating T4 then the end of the train initially at 265m needs to get up to 800m in order that the Up/Down crossover can be normalised behind it.
Given you have calculated that it takes 50m to accelerate up to 25km/h, then I think the length to be travelled at that constant speed would be 800 - 265 - 50 = 485m. Hence I basically agree with you but it wasn't obvious to me where you were getting the 440 value from, so a little further explanation would have been good.
Possibly should have stated some more assumptions (the main one being that there is no traffic from the Up Main nor use of the adjacent platform; I really don't understand why the question gave the station layout yet told you to consider only one element of the apparent traffic), but otherwise your answer demonstrates what I think the question required, showing as it does an understanding of the signalling operational logic as well as the Newton's Laws calculations.
A few small points
1. I don't know whether it was luck or skill that placed signal 29 at 300m from the point and this happened to turn out to be the distance needed to brake to turnout speed! Actually the speed restriction through the points applies to the curved path through the turnout and its approach (as not possible to cant it appropriately for the radius of curvature because of the need to join smoothly with the straight line) and thus in reality would apply at latest say 50m prior to the switch tips, but that is just a quibble.
2. The calculations are not exactly consistent with the demarcation line drawn separating T2/T3; it was a good presentation to show what you were going to calculate, but for the benefit of anyone else looking to tie the numbers with the diagram it is worth stating that this showed your initial assumption which was actually later refined when the numbers were produced, since the braking to a stand would actually not be necessary until well into the platform.
3. As I see it, the datum for the commencement of the platform is at 400m and you have decided to stop the 120m train centrally within it and thus have a 15m allowance at each end. Surely then you have the RH end of the train at 385m and the LH at 265m. When calculating T4 then the end of the train initially at 265m needs to get up to 800m in order that the Up/Down crossover can be normalised behind it.
Given you have calculated that it takes 50m to accelerate up to 25km/h, then I think the length to be travelled at that constant speed would be 800 - 265 - 50 = 485m. Hence I basically agree with you but it wasn't obvious to me where you were getting the 440 value from, so a little further explanation would have been good.
Possibly should have stated some more assumptions (the main one being that there is no traffic from the Up Main nor use of the adjacent platform; I really don't understand why the question gave the station layout yet told you to consider only one element of the apparent traffic), but otherwise your answer demonstrates what I think the question required, showing as it does an understanding of the signalling operational logic as well as the Newton's Laws calculations.
(24-11-2011, 11:35 AM)onestrangeday Wrote: Hi PJW: Sure, many thanks.
PJW