West Coast tilt speeds

I note that Alliance Rail Holdings has received approval to run Class 91s and Mk 4 coaches to Blackpool from September 2019, initially with a 110mph maximum speed ( RAIL 856).

From a track engineer’s Mk 1 backside perspective, this will be very interesting. The ‘91’/Mk 4 combination on the East Coast Main Line really ‘hangs it out’ round the more curvaceous parts of the ECML, because BR Eastern Region set the permissible speeds on the basis of 150mm cant plus 150mm cant deficiency (uncompensated lateral acceleration).

Pendolino passengers feel very little deficiency because the tilt compensates for most of the lateral forces. Quite what passengers will make of these different styles of ‘ride’ between Euston and Preston remains to be seen!

The BR (LM) civil engineers were also far less ‘progressive’ when setting maximum permissible speeds, as reflected in the lower 110mph non-tilt line speed on the West Coast Main Line (WCML), although this was also influenced by the limited design speeds of the Class 86 and ‘87’ traction.

The news item implies that there will be a review of non-tilt permitted speeds on the WCML, and it will be interesting to see what speeds (both above and below 110mph) ultimately prove possible without tilt but with 150mm deficiency - I hope the LNW Route seeks advice from LNE Route on such matters.

But there really ought to be a review of tilt speeds, too. There were a number of areas where the full (or indeed any) potential of tilt was abandoned in the attempt to curb the runaway costs of the WCML upgrade project. The excellent ride on the WCML today shows that the track engineers have mastered the quality needed for Enhanced Permissible Speeds (EPS) over the past decade, so why not revisit some non-EPS sites to see what can be done? Jim Wheeler, Surbiton