Question was asked of me - with extra signals between Thingley and Bradford Junctions, could trains follow each other in the same direction and so get more trains through? In ideal world, where there's plenty of capacity on the double track lines at both ends, and where trains turn up spot on time, yes. But this is not an ideal world.
I've taken a look back through the last week using Real Time Trains, and 149 trains have run out of what would be 183 in a typical normal week - 10 freight and 24 passenger services lost. Freight trains varied from being 65 minutes early to 108 minutes late, with only 10 of them being on time or within a couple of minutes. On the very best day of the week - Monday - one train still turned up 25 minutes early.
So what would it need to provide an hourly passenger service on this line? It could be done with freight operations remodelled around the single line - turning up reliably at Bradford or Thingley Junction at the time they have been allotted and proceeding through the line ans away from the are as planned. That ain't going to happen!
You need passing and / or overtaking loops (plural, I suspect) on the single line section or perhaps redoubling it whole way between the junction. You then have the local infrastructure to one half of the hour for a passenger train each way - passing in the middle, and for the other half hour to be a freight train each way - again passing in the middle should both paths be used. And you have some of that capacity to put a freight that's at the wrong time out of the way while awaiting an opportunity to move on - remember that you have busy main lines at both ends!
The question was also asked if some of the passenger trains coming up from Westbury could reverse at Chippenham, and then go to Bristol, serving Corsham. Great theory in the immediate Chippenham area - xx:00 arrival into Chippenham platform 1 just after the xx:56 has left for London, Bristol train leaves at xx:08 and then the Bristol via Corsham service leaves at xx:12. The other way - service from Bristol arrives Chippenham platform 2 at xx:20, ahead of the xx:25 call of the London train at platform 1. It then sets off for Westbury at xx:25, clearing the main line in time for the xx:32 Bristol service. The Westbury-bound train passes the Bristol-bound one in the re-instated loop at Holt Junction. All of which is a grand dance until you look to add freight into the mix, or until anything gets delayed. Or until you start getting people about the long waits at Chippenham when they're used to all services going to Swindon.
Re-instatement of platform tracks at both Chippenham and Westbury would be, I think, almost vital for a robust setup in this area of main line interaction and heavy freight. And having those platform tracks in the form of loops, capable of being used by expressed and long freight trains would also make sense.
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