I suggested an electric stopping service from Cardiff to Oxford via Temple Meads & Bath as this would act as a link between all the intermediate stations such as for example, Severn Tunnel Junction to Keynsham & allow for longer direct journeys such as Chippenham to Filton or Temple Meads to Oxford. Clearly, south Wales to Oxford passengers would go direct to Didcot & change.
Having the stoppers, also allows the Cardiff to Portsmouth trains to run through the area calling at main places only. These trains should as I said earlier, be bi-mode and as such, further justifies the cost of getting these lines electrified.
Severn Tunnel: In HST days, I could smell the diesel fumes inside the coaches - not helped by people leaving open windows at the non electric doors.
I can’t see the public shutting the hopper windows on the 165/6’s when they go through long tunnels. I think that in the days of steam, passengers would close the sliding windows when in tunnels.
As air pollution in Bristol is so bad, the Council have set up a zone where polluting cars have to pay a fee if they enter the zone. This has caught many people out as it includes the A4 in the Avon gorge - a route used by motorists to reach the out of the way Airport from the M5 and Severn Bridges. All the more reason crack on & electrify the railways in the Bristol area.