Appendix W, Activity 1A - Q8

[savitha kandasamy]

Generally seem to have made a good attempt.
You correctly determined that it is the passenger train rather than the freight train which is the more onerous constraint regarding the minimum signal spacing for braking, but it would have been good to have stated this explicitly.

Conversely you do not seem to have considered whether the capacity requirement needed for the freight trains at night gives rise to a more onerous constraint on the maximum spacing than that imposed by the passenger train required headway, or indeed the maximum amount of ove-rbraking considered tolerable.

Also in the exam don't just quote the formula re Headway, but explain using a diagram its derivation.

As per the operational requirements for passenger trains,

Minimum Signal spacing = 0.5*BD1 = 0.5*2025 =1013m
Maximum Signal spacing, d =((Ht4*Vh)-(S+O+L))/3
= ((120*36)-640)/3
=1227m


As per the operational requirements for freight trains,

Minimum Signal spacing = 0.5*BD2 = 0.5*1458 =729m
Maximum Signal spacing, d =((Ht4*Vf)-(S+O+L))/3
= ((180*27)-850)/3
=1337m


The longest braking distance needs to be considered to ensure safety. So the minimum signal spacing is 1013m.

For Maximum signal spacing, if we considered freight train headway requirements as more onerous , we can place the signals at 1337m. This is within 33% of BD. But the headway requirements for passenger trains cannot be achieved with this maximum signal spacing. Also I am not sure how the braking distance requirement for freight will fit with the maximum signal spacing (if we choose either 1227m or 1337m). Kindly suggest me how to justify for the operational requirements for freight trains.

savitha