20-09-2010, 04:06 AM
Oh, I see... Thanks......
(19-09-2010, 08:24 AM)PJW Wrote:(19-09-2010, 08:11 AM)greensky52 Wrote: Then even if 3 aspect is avaliable in some layout, but signal spacing of 4 aspect is 0.5*B.D, which must be smaller than 3aspect--B.D. So if the question asked like this one, we should choose 4 aspect to calculate headway?
I obviously do not know what the examiners would expect; all I can say is what I would do if a candidate.
My logic is that
part a) says: Determine minimum braking distances for the permissible speeds and braking characteristics of the traffic on offer.
Therefore I would do that for the various speeds / braking rates mentioned.
part b) then says: b) Determine graphically, or by calculation, the headway at minimum signal spacing and the given speed for........
Since this makes no reference to the layout and its headway requirements but only asks what the headway would be at minimum signal spacing, it seems logical to me that 3 aspects are assumed . Potentially could cover yourself by also calculating for 4 aspects spaced at 0.5 BD- I suppose it would not take long to do so and therefore probably worth it. Of course, in the exam always have to decide whether any time spent would be better employed doing smething different that may get more marks per minute......