To me it doesn't really make sense.
Reading has maintained these since they were new and have the experience, which SPM doesn't have. Look at the state of 166s since they transferred west, they've gone downhill massively since they were Reading based.
Plus it seems like a massive waste of fuel transferring 165s to and from Bristol. I'm struggling to see the advantage here.
How is it a waste of fuel when it’s been explained the changeover take places at Worcester.
The advantage is so there is capacity within Reading Depot to maintain the class 769s which will be working on Thames Valley services - how else do you propose these are maintained bearing in mind they are longer and take up more shed space than the turbos they replace…. The front line railway doesn’t do things for the sake of it!
RE 166s, when they were at Reading most units either got back to Reading each night or stabled at Oxford. At Bristol the 166s have a tough life with over half the fleet outstabled every night at places such as Fratton, Weymouth, Westbury and Gloucester. A fleet with returns more often to its Home Depot will be by its nature more reliable.
The rebuilt Exeter depot will take over some of the works on 158s from SPM which will alleviate pressure there.