G23 Activity (2004 layout calculation)- comments please

[PJW]

Hello Peter,

You are absolutely correct. It was supposed to have been the non stopping calculations for the G23 Activity Calculations. Please have a look as the train separation for headway, Green to Red and N values are very different from those given in Appendix W, Activity 1B Headways and Braking Calculations.

Look forward to your comments.
Thank you and Regards

You have only given me the results rather than your workings which led to them so I am having to do some reverse engineering- that is why in the exam you MUST show examiners HOW you get to the result.

However by deducting the "Green to Red" figures from the "120 second headway" ones gives 895m in each case (except 890m in top row). For the stopping headway you have said you are assuming 225m overlap and 200m train length so that makes me think that you must have assumed a Sighting allowance of 895-225-200= 470m. At the headway speed of 100km/h this suggests you are giving the driver 17 seconds observation time. That really is rather "over the top" and would explain the discrepancy between the figures. The Minimum Reading Time for a signal does depennd on a variety of factors including signal complexity and obscurations but tends to be around 8-9 seconds. For calculating headway it is sensible to recognise that drivers nowadays are encouraged to brake upon observing a cautionary aspect and thus I think 12 seconds is sensible to reflect that some signals do have more than the minimum sighting. Where signals have extremely good sighting I think drivers do use some common sense and don't start braking when they see a cautionary aspect in the far distance.

So did I guess right; how did you calculate the penultimate column?