3.1.58 Whilst the fast lines are grade separated the slow lines still join the Wakefield
lines with an at-grade junction. To generate the required system capacity and
regulation of trains, an important operational feature is that slow line chords
are required between the proposed Ravensthorpe East Junction and a re-
modelled Thornhill LNW Junction. In simple terms, this is a piece of plain line
in-between the junctions where trains, if required, can lay over “pause” whilst
awaiting a clear signalled path. Without these chord lines the new junction
would not function as required, due to slow trains becoming stationary on the
preceding 2-track section from Leeds whilst waiting at a clearing signal. At
this location slow trains are being quickly “caught” by the next timetabled fast
service (see previous commentary), therefore a layout without a regulating
chord would severely inhibit capacity and associated performance of the
system. See illustration sketches below showing how chord lines are
arranged for the different operational layouts.
...
3.1.61 At GRIP2 it is understood that the slow-line chords were initially sized to
accommodate possible future freight train lengths of up to 750m. In practise,
there are no current plans to operate such long train formations over the
Leeds route (in normal service), and as part of the GRIP3 development I
proposed that the minimum the chord lengths under consideration should be
sufficient to stable a 200m long passenger services (in accordance with the
ITSS) exiting or joining the through main line. For a 200m long train,
considering signalling and track geometry factors, it was established that the
chords needed to be an absolute minimum overall length of about 600m was
required to provide safe separation of trains. In addition to establishing the
minimum chord lengths, the following principles were used to generate the
junction and linking chord geometries at Ravensthorpe:
• All slow line routes through junction switches and crossings (S&C) and
adjoining chords should enable 70mph running. This allows trains to run
as close as practicable to the existing 75mph linespeeds utilising
standard S&C track components for ease and speed of future
maintenance.
• The through route for TRU fast trains is proposed at 100mph (or more) to
exploit the most efficient and cost-effective line speed capability of the 4-
track route section to the west of Thornhill LNW junction (towards
Mirfield and Huddersfield).
• Critical S&C track components should remain clear of underline
bridge/viaduct structures to minimise faults due to vertical deflection,
twist, and temperature movements. In practical terms, with consideration
of stabling chord lengths, this limits the position of the new Ravensthorpe
East Junction to the east side of any proposed viaduct and/or
embankment over the River Calder flood plain.
• Junction S&C components should be where reasonably practicable
located on straight track at a constant gradient and where joining tracks
are vertically coincident.