10-05-2010, 08:19 AM
P32 of GK/GN0802 gives a definition for both POL and PROL. I have seen several but the most memorable is the signal protecting the crossover on the up, country side of Ebbsfleet High Level.
It has a PROL as there are routes over the crossover bang road as occassional reversing moves or to the sidings. Hence, the platforms could both be full. The approaching train from the North Kent is signalled off that line to clear it for operational reasons. However, the approach is 1:40 until 20m in rear of the pin.
So, a ROL was introduced to allow the North Kent to EBB HL route to be set when a route from the station (down) across the crossover was set. However, from memory, the ROL is within the fouling point on the straight ahead route for the up line. It could not be on the diverging route due to the points being locked by the down route being set. Phantom, because it doesn't actually exist!
The approach to the pin was mitigated by a TSS and three OSSs mostly due to the gradient but part of the mitigation was the infrequency of the opposing move occuring despite the effects, due to the topology, being significant. It was the layout that forced a solution and the mitigations were complex.
Hope that helps. If you want more info, I will try to find the scheme and some of my notes.
Jerry
It has a PROL as there are routes over the crossover bang road as occassional reversing moves or to the sidings. Hence, the platforms could both be full. The approaching train from the North Kent is signalled off that line to clear it for operational reasons. However, the approach is 1:40 until 20m in rear of the pin.
So, a ROL was introduced to allow the North Kent to EBB HL route to be set when a route from the station (down) across the crossover was set. However, from memory, the ROL is within the fouling point on the straight ahead route for the up line. It could not be on the diverging route due to the points being locked by the down route being set. Phantom, because it doesn't actually exist!
The approach to the pin was mitigated by a TSS and three OSSs mostly due to the gradient but part of the mitigation was the infrequency of the opposing move occuring despite the effects, due to the topology, being significant. It was the layout that forced a solution and the mitigations were complex.
Hope that helps. If you want more info, I will try to find the scheme and some of my notes.
Jerry
Le coureur