Great Western Coffee Shop

Another item to the Easter 2015 commissioning is the removal of all relay-controlled signalling in the outlying areas (Cholsey, Goring, Tilehurst, Scours Lane, Twyford, Ruscombe), so it's all under the control of the Computer-based-interlocking (CBI) at TVSC.

This ought to be invisible to the end users - the majority of "new" signals are in the same places, and show the same colours, to the trains as before.  But "underneath", there's a lot of old electro-mechanical hardware, and multi-core copper cables, that can be removed.  So this ought to make it much more reliable.  Many of the recent signalling problems have been with keeping the old kit working.

I don't agree with that.  The old signalling is very reliable (its mostly been in use for 50 years now).  Its the new kit that always is unreliable when first installed (its called the 'bathtub curve' effect).

Maybe after 50 years the performance of the old signalling equipment is now crawling up the other side of the bath tub, when everything around it is being given a swirl ...

... by floodwater.  ::) :o ;D

Well, that's as maybe when the old signalling is left undisturbed.  But with control being migrated from Reading PSB to Thames Valley Control Centre, there are substantial changes to the operation of the railway. 

In the PSB days, the signaller would set the route long before the train reached any restrictive aspects.  If the signal didn't clear, he'd try again, or possibly swing some points using the point key switches.  Then, after passage of the train, he'd cancel the route.

Now, with IECC and ARS operating the railway, ARS sets the routes only just as they're needed.  If there's any need for a retry (if the route doesn't set, or if a set of points don't swing, possibly caused by a sticky relay), then there's a much shorter time window before the train driver sees a double-yellow and starts braking.  Similarly, after passage of the train, the tracks have to pick at exactly the right times for the TORR (Train-Operated Route Release) to work.  So with less human intervention, there's less resilience to equipment mis-operation.

A big proportion of the faults I've investigated for this area have been related to the relay rooms.  I for one will not mourn their passing - not least because there's much better logging of what's happening inside the Computer-Based-Interlockings.

When BT was privatised they massively reduced their costs by replacing all the relay based exchanges with electronic ones! This allowed them to reduce their maintenance staff substantially. 

... and that opened a whole can of worms as BT then had to let competitors install equipment in the space made free.