2011 Headway calculation

[Zaphod]

Hello,
I have recently joined the IRSE forum with the intention to sit the IRSE exam this year.
It's been a while since I tried any headway/ braking distance calculations and I would be grateful if someone would be kind enough to look over my calcultions and provide some feedback.

Kind regards
KJB

Hi KJB,

I noticed in your answer that the headway for 4-aspect signalling is greater than that for 3-aspect, which is the opposite of what I would have expected. I think the reason this has happened is because you have set BD1,2,3 equal to the required braking distance. Under 4-aspect, the distance between signals only needs to be half of this value. So BD1,2,3 need to be set to something like 986 m (for 4-aspect only).

I think your definition of the headway time in your equation is correct, but where you have written it out in words you have omitted a couple of terms, as Jerry said.

For part b, I am not sure how valid the assumption is that the time taken to accelerate back up to line speed can be disregarded. In reality, I would expect this, as well as the time taken to come to a stop at the station, to be an important component of the additional headway time. I would suggest that the best way of addressing this in the exam would be to add a (v-u)/t term, which covers both the time taken to decelerate and subsequently accelerate.

I think that adding a contingency of say 5% is not a bad idea (indeed it is exactly what we do in reality!). However, what you have added is more like 1%.

Overall I think it's a pretty solid answer and just requires a couple of tweaks and additions.

ZB