"TPE, CAF, Hitachi and Network Rail have undertaken extensive modelling to assess the requirements for non-tilting 125mph operation. The overhead traction equipment (not least the tension of the contact wire), signalling distances and vertical alignment (even a railway has to consider vertical accelerations to keep passengers comfortable and track materials intact) are 125mph-capable without any alteration.
Only curving forces present an issue, and having identified several test sections, CAF in particular have been running their Class 397s at the proposed speeds and ensuring that comfort in the passenger saloons isn’t impacted. Testing of this aspect of the new trains’ operation has shown that 125mph without tilt is comfortably feasible, and that the better acceleration of the units allows them to make more use of the short straight sections between curves. If all goes to plan, then the WCML north of Preston should be signed-off for 125mph without tilt in the middle of next year.
"......., some pragmatism from rolling stock and infrastructure engineers has gained a quick win for passengers. 125mph operations without tilt are happening as you read this issue of RAIL [edit: not passenger service though, that has to wait for the new speed signs to be put up, which looks like it won’t happen before the middle of 2020].