On 11 Jan, 18:28, (Neil Williams)
wrote:
Does anyone know the purpose of the apparently approach-controlled
signal in the middle of the platform on the westbound Moorgate
Met/Circle/H&C platform?
My best guess would be that it allows more flexibility in setting the
route for trains into/out of the terminating platforms. I would think
the overlap from the westbound starting signal to the fouling point of
the lines to the bay platforms is not sufficient to allow approach
into the westbound platform at line speed, and therefore an approach-
controlled signal in the middle of the platform would make sure a
train that overshot the starting signal would be tripped and stopped
before getting into a conflicting position with the bay lead.

Hopefully Clive Feather (sadly not seen as frequently here as
previously) or someone else will hopefully provide a definitive
answer, or you could try on District Dave's Forum -
http://districtdave.proboards39.com/index.cgi - for an almost
guaranteed answer.