If my knowledge serves me well I believe that Derby to Chesterfield was upgraded from 90mph to 110mph as part of the same project. I find it irritating that the linespeed through Burton-on-Trent wasn't increased at the same time, maybe not quite 125mph as per the rest of the line, but something much higher than 50mph. Is this restriction in place due to signal spacing in the area not supporting higher linspeeds?
It's a shame that other parts of the CrossCountry network didn't receive the same treatment, Bristol to Birmingham being an obvious candidate, but that would have been a much more difficult job given the number of foot/level crossings on the route, as well as the random kinks on an otherwise straight route. Another irritation is the three-aspect signalling; Really there ought to be four-aspect, with new signals placed in-between the middle of the existing block sections. If a Cardiff to Nottingham train gets delayed and leaves Birmingham New Street after xx:49, it doesn't' take long for the following xx:03 train towards Edinburgh to catch up to it and be chasing single yellows over 1.5 mile long block sections, especially if the Nottingham train calls at Wilnecote.
Its also worth pointing out that the line uses HST differentials for linspeeds above 90mph, covering every class of passenger train using the route, but not including non-HST trains to go beyond 90mph would have saved some money, presumably so that the signal spacing wouldn't have needed to have been changed.
I don't intend to come across as bashing the upgrade, however, were another upgrade to happen, perhaps as part of electrification once the MML is electrified, there are a number of ways in which the route could be improved, including remodelling junctions, especially the Kingsbury area in which trains coming out of the oil depot have to reverse onto the mainline to head north.
