A2250 at Farringdon

[Deleted]

I was at Farringdon today and noticed that A2250, a draw-up signal associated with the Outer Rail starter, was only two-aspect. Confusion reigned when it cleared to single yellow.

What exactly is the purpose of a two-aspect draw-up signal whose proceed aspect is single yellow?

[Tom]

At a guess, speed control on A225 such that you should never see it display a green aspect from the location of the draw-up?

[Deleted]

But why bother speed-controlling A225 anyway? The curve east of the station doesn't seem sharp enough to warrant such a thing.

For that matter, why isn't A225 a controlled stick in the OH series anyway?

[Tom]

Ah... read 'Farringdon', thought 'Barbican'.

Might also have something to do with the fact that a green on A2250, if seen by a driver coming over the crossover, could be interpreted as permission to go at full line speed with the rear of the train over the crossover (part of a shunt move, 15mph max).

Why not controlled? I'm not too sure. It might be that because there are no points involved and as a train would have to shunt past it to reverse over the crossover an Auto signal would be the simplest way of doing things.

[Deleted]

This of course begs the following questions:

1. Why is the crossover protected by OH37 in the position it's in?

2. Why is the precise shunt-past-starter arrangement you just mentioned in use at West Kensington?

[Harsig]

A 225 is approach controlled such that it will not clear until the train has passed A2250.
A2250 was installed as recently as 1999 and was probably provided because of the limited overlaps that exist in the area and this is probably also the reason A225 is approach controlled.

[Deleted]

Before the installation of A2250 at Farringdon, the inner home OH47B was a 'bottleneck' on the section from Baker St to Aldgate. The problem was that a train standing at A227A (Barbican outer home) kept OH47B at danger, reducing line capacity at that spot.

A2250 has evened-out the line capacity along that whole section.... so even when the service is blocking-back a little, the flow is more even and steady.

[citysig]

Pete said:

A2250 has evened-out the line capacity along that whole section.... so even when the service is blocking-back a little, the flow is more even and steady.

Really? Oh you mean on paper, without adding those C-stock drivers due off in 3 Circle's time ;D

Mind you yesterday a Met who had dragged his heels all trip refused to leave Barbican eastbound as he could see the following signals were at danger. Unless we intervene they will be as the computer calls for them after the train leaves Barbican. We could have been there all day ;D