I really do wonder whether the first A48 road bridge over the mainline west of Cardiff Central would be high enough for overhead wires to pass underneath in the event that they electrify Cardiff to Swansea? I can’t see how the line could be lowered at this point as it is right by the River Ely. Recently, a very expensive low level road viaduct was built into the new Ely Mill development area. I really do wonder whether a new bridge for the A48 over the railway at this point would have been a better option in order that the present bridge could be removed? That would have been one less expensive problem to overcome should they electrify west from Cardiff being as they built this new road in any case. You can see the location here:>
https://www.google.co.uk/maps/@51.4842823,-3.2267474,661m/data=!3m1!1e3!5m1!1e1
If they just assumed that only one IET per hour would make use of the wires between Cardiff & Swansea, then that is surely wrong? During the peaks, 2 IET’s per hour run along this line. Having the local stoppers electric would also have given a better cost v benefit ratio.