It's not an improvement, though. It's worse than what was there before, which was 125mph line speed.
No, the current line speed for electric trains is, and always has been 60. It is being raised to 110 for electrics. The Diesel speed limit has been 125mph since the 1970s, and isn’t changing.
If IETs run at 110mph Electric rather than Diesel 125:-
1) Trains departing Didcot westbound on Electric will make significant time saving (perhaps as much as 2 or 3 minutes, I haven’t seen the modelling) vs current situation where they
must depart Didcot on Diesel.
2) Trains passing Didcot in either direction, or stopping eastbound on Diesel won’t have to undergo a traction changeover. During the changeover process the speed will usually bleed down to 100/105 anyway, the GUs not having the grunt to regain/sustain 125mph running in such a short section. On Electric theylll be able to hold 125 right until they need to brake for the bridge (quarter of a mile tops), and have the power on tap to quickly return to 125 running after the bridge. Again time savings to be had.
There is no quantifiable downside to the solution vs the status quo. Yes. Demolishing and replacing the bridge would have allowed 125 electric; but not in the timeframe that linespeed improvements are required. And there’s nothing ruling out 125mph Electric on existing infrastructure after further modelling and testing; although NR aren’t going there yet.
Meanwhile the local residents - who would have suffered significant disruption of the bridge were demolished - don’t have to bear any disruption at all. It is correct that their objection had no legal basis; but it made Network Rail think about non-disruptive methods of solving the problem.