09-09-2008, 08:16 PM
dfreer Wrote:Thanks PJW, much appreciated.
I think my layout might be slightly different to yours as my destination 'F' is a level crossing but I take your point.
Oops sorry! I took the adjacent (2001) layout out of my folder in error!
In reality for the 2002 layout I suggest the calculation should initially assume that the train entering the branch keeps at 40km/h until braking to stop in station . If that worst case achieves the headway then solution is obviously OK, otherwise then calculate how much time could be saved if train accelerated for a short length (couldn't accelerate until last vehicle had passed over the branch points) prior to decelerating again to a stop in station.
[NB. Assuming the junction signal had only displayed yellow + PLJI, we wouldn't really want to encourage the driver to accelerate after the speed restriction, seeing that would be approaching a red]
For the opposite direction perhaps it is more reasonable to expect the driver to accelerate to more than 40km/h and then slow again to take the junction.
The more general issue is that it can be sensible to approximate to make the calculations easier, but do ensure that you do so in a way that addresses the worst case. Round UP braking distances, round DOWN the non-stop headway distance, assume the lower speed for headway calcs where speed varies etc.
PJW
PJW