In general they seem fine until you lose me a bit on the last page.The easier way to calculate the time taken to decelerate at constant bake rate to come to rest (especially where that rate is 0.5m/s/s) is to take the inital speed and divide by the rate- train initally at 33.3m/s and in every second it loses 0.5m/s then clearly it will take 66.6s to stop.
Para re acceleration being symmetrical with braking is true, but not sure what use you are making of that fact.
The times you calculate between train claering the overlap and covering its own length are based on 33.3m/s. Looks to me as if when you say "the signal" you were thinking of the signal one section on from the station. However the pinch point as far as capactity is concerned is for the section which includes the station- afterall for 30 seconds the train is not moving at all and it also is moving slowly as it arrives and departs. All this time the signal protecting the station is held to red and it is this (and the consequential restrictive aspect at the outer signal) that is giving the capacity constraint.
So although you have got the individual elements,you are not quite calculating what you need to do. The calculation for the train to move its own length plus the length of the overlap is from the standing start at the station.
Let's consider station B.
Until the rear of the earlier train has cleared the overlap beyond signal 23, signal 19 is held to red and therefore the outer signal (which if we work on the basis of you disgram as it currently exists) is signal 15 that can only be at yellow. Therefore any driver seeing this signal would not accelerate up to their usual speed as they would know that the next signal could be at red and therefore they would have to limit their speed so that they could stop within the distance for which it is visible, or else they risk SPADing it.
Much the same would be true if there were an intermediate signal 17 in the length between the stations. What we are trying to calculate is how far away from station B we could place this signal and yet still get it to show a green by the time that a driver approaching at their normal running speed first sees it, so that we avoid them needing to brake.
Then we use the method of calculation you have deployed to add the time that this 2nd train the needs to get into the station and dwell so that it is itself ready to leave, with the time the first train took to accelerate so that its rear end had cleared the overlap beyond signal 23.
There are some similarities between this layout and a previous IRSE Exam layout; have a look at this thread re 2000 Headway Calcs and layout
In particular I have placed a couple of attachments with graphs of stopping headway for 3 aspect and also a comparison between providing 3 aspect and 4 aspect signalling.
Para re acceleration being symmetrical with braking is true, but not sure what use you are making of that fact.
The times you calculate between train claering the overlap and covering its own length are based on 33.3m/s. Looks to me as if when you say "the signal" you were thinking of the signal one section on from the station. However the pinch point as far as capactity is concerned is for the section which includes the station- afterall for 30 seconds the train is not moving at all and it also is moving slowly as it arrives and departs. All this time the signal protecting the station is held to red and it is this (and the consequential restrictive aspect at the outer signal) that is giving the capacity constraint.
So although you have got the individual elements,you are not quite calculating what you need to do. The calculation for the train to move its own length plus the length of the overlap is from the standing start at the station.
Let's consider station B.
Until the rear of the earlier train has cleared the overlap beyond signal 23, signal 19 is held to red and therefore the outer signal (which if we work on the basis of you disgram as it currently exists) is signal 15 that can only be at yellow. Therefore any driver seeing this signal would not accelerate up to their usual speed as they would know that the next signal could be at red and therefore they would have to limit their speed so that they could stop within the distance for which it is visible, or else they risk SPADing it.
Much the same would be true if there were an intermediate signal 17 in the length between the stations. What we are trying to calculate is how far away from station B we could place this signal and yet still get it to show a green by the time that a driver approaching at their normal running speed first sees it, so that we avoid them needing to brake.
Then we use the method of calculation you have deployed to add the time that this 2nd train the needs to get into the station and dwell so that it is itself ready to leave, with the time the first train took to accelerate so that its rear end had cleared the overlap beyond signal 23.
There are some similarities between this layout and a previous IRSE Exam layout; have a look at this thread re 2000 Headway Calcs and layout
In particular I have placed a couple of attachments with graphs of stopping headway for 3 aspect and also a comparison between providing 3 aspect and 4 aspect signalling.
(06-11-2011, 04:50 AM)onestrangeday Wrote: Sure, it's great help PJW.
I'll wait for your comment for my calculation.
thanks
(05-11-2011, 07:52 PM)PJW Wrote: I look at the calcs later. In brief:
PJW