Would redoubling need to take place (assuming a decent passenger service has started)?
That's a very tough question, but (ball park figures) there is current capacity for one train each way, alternating, per hour - so over 18 hours that's 36 journeys. Add a coupl of extra signals and let co-ordinaye the freight with the passengers, and that could go up to around 60 journeys.
Currently there are 4 passenger journeys, leaving 56 paths free for freight before you double. After December, there
will (we hope) by 12 passenger journeys, and I'm going to project that up to 20 (train every 2 hours, from 6 a.m. to 10 p.m.), leaving 40 for freight, in 5 years time with just extra signals.
It's when you want to start running three trains each way every hour that things start to get to the "gawd - this needs to be double" stage although it would be wise to add refuge loops (say) at Thingley and Bradford Junctions well before that so that a degree of further robustness if provided. The Business Plan calls for such extra loops between Didcot and Oxford, and it would be natural to put in more on the Chippenham to Trowbridge section.
