My understanding (non-professional!) is that ARS^▸ (Automatic Route Setting) aims to set routes so that each train has two greens ahead where possible. So an incoming train will trigger ARS to set up the route into Paddington when it is still x distance away - so if the 1736 hasn't had its route set / TRTS^▸ (Train Ready To Start. A plunger/switch pressed by platform dispatch staff that informs the signaller that a train is ready to depart.) pressed when the incoming train has passed that 'x' point the line will be considered clear and the incoming train will be routed into the platform. A human might notice that the inbound HST^▸ (High Speed Train) has a few minutes to spare and have a quick check for imminent departures - but would ARS consider that?

I think the answer might lie in this quote from the Rules of the Plan for this area ^ http://www.networkrail.co.uk/browse%20documents/Rules%20Of%20The%20Route/Outrotp8/gw08p.pdf ^ page 95:


Obviously on the final approach to Padd there's not much that can be done, apart from signallers staying on the ball and intervening soon enough if they're aware of any regular problem cases like the 1736 seems to be. I suppose platform staff being aware and operating TRTS 'too' early might look like a solution but I could see that being a problem itself (and would ARS just ignore until nearly 1736 anyway?).

I usually Google for 'Rules of the Plan' when I want to refer to them. Quite a big, dry document - the dwell times are  in Section 5.3.5 (under the Bookmarks tab on the left in Acrobat Reader). Route GW103 covers PAD^» (Paddington (London) - next trains)-RDG^‡(resolve); GW500 covers the Berks & Hants. For Turbos the 'standard value' is 30s (1m for non-DOO^▸ (Driver-Only Operation (that is, trains which operate without carrying a guard)) routes like the Cotswolds) - so for a HST^▸ (High Speed Train) to be faster with a few stops, there has to more sustained 100+mph running. Interestingly, it's only in recent releases of the rules that it's been 30s - it used to be 45s, which in practice means alternating between 30s and 1m. Incidentally, minimum timing allowances are also shown (sec 5.5) - on a Paddington-Bristol/Cardiff run it's more or less a minute's slack per stop - similarly, it's easy to see how a non-stop run on the B&H^▸ (Berks and Hants - railway line from Reading to Taunton via Westbury) can arrive at Reading 5 minutes early.

Most of the stations affected by the new HST stops had loco-hauled trains on similar peak semi-fasts before the Turbos came - I wonder what dwell times were like then. Hopefully passengers will become better-trained in time. I say 'hopefully'...

True, but I assume a bus would make a significant difference to the total loss by keeping arrivals at least as far as Swansea within the hour, and Newport (along with Manchester-direction connections) if the bus made the 17xx off Carms, and halving the value of London claims...

(Edited a bit - hopefully clearer :-))

I was intending to use the Pembroke Dock - Paddington train - there seemed to be a minibus serving the less busy part of the line beyond Tenby - presumably supplemented by a coach or two from Tenby. I imagine it's better/cheaper for FGW^▸ (First Great Western) to provide replacement transport than pay out the refunds for the delay caused by waiting for the next train (over 1 hour's delay, and two for London and similar flows - full refund) - plus I don't think everyone would have fitted onto the pair of 153s forming the next train! When I got home Live Departure Boards were saying the train had started at Swansea.

This seems to have happened at least once a year in recent years on this train, often on the key bank holiday weekends - not a good advert for the one-off travellers, families etc who might be using it! Is there a problem with too few drivers having route knowledge - I guess not all FGW Swansea drivers sign it, and they probably need refreshing each year, and swapping drivers at last minute could mean cancelling one of the hourly SWA^» (Swansea - next trains)-PAD^» (Paddington (London) - next trains) trains, whcih in the big picture is probably less desirable.

If you're interested, you can check the official minimum dwell times used for timetable planning in the Rules of the Plan, which can be found easily by Googling. The dwell times recorded above actually do (Newbury is an exception) match the official allowances reasonably well! At most of those stations, for HST^▸ (High Speed Train) it's 1 1/2 minutes off-peak, 2 minutes peak; at Reading and Westbury it's 2 minutes all day.