Killingworth
Established Member
Since the new chord round the west to east curve at the triangle seems to be longer, perhaps they could install a set of points where it veers off, to make it an effective loop; it looks plenty long enough to hold a 6 car train for a short time.
As I said in my last post the cant to allow the loop to take the sharp curve would make that very difficult. It was looked at early on in the planning and discarded for that reason. The loop track is laid to rise into Dore tunnel, the MML and Bradway Tunnel. It's also lower to the inner and wooded side of the bend and higher on the side adjacent to the mainline track.
To enter the loop where the two tracks are both level would reduce the effective length. When, eventually, the track for the loop is finally laid (11th February, all being well) we'll be bettee able to see that..
Otherwise I'd agree it's a fairly simple and good idea. Cost, two sets of points, signalling and more earthworks?
If I'm understanding your proposal correctly, you'd be cutting the effective length of the chord, which was a major aim of the project. Looping the stopper at or near Dore is not the correct solution, the focus should be on getting the TPE to run to time and asking why that doesn't happen, because then nobody would be suggesting infrastructure solutions costing tens of millions of pounds if the timetable was kept to.
Providing an additional set of points off the eastbound track at Dore would be difficult with the curvature (although not impossible), require greater interlocking and also prevent freight trains being held on the curve clear of the MML (again, this was a MAJOR goal of this project) due to the curve being effectively back to what it was. You would also likely cause major issues with the cant of the track as points (for obvious reasons) have very small tolerance for any cant in the curved leg. Nice idea but sadly there are good reasons why it hasn't been done.
Providing bi-di through Dore would have been very difficult because of the curvature of the track and the presence of the bridge immediately north of the junction on the MML, so the facing crossover to allow westbound trains to get to the wrong line would have had quite big margins against the Down MML, and then it's an extra 2 sets of points to maintain on the MML, in addition to the additional crossover at Totley Tunnel east, and all the associated interlocking for the additional routes at each junction and through Dore & Totley station.
For every extra difficulty it costs more to solve, at some point, you are spending more money than the benefits you are gaining.
It would not require a reduction in the effective length of the chord, or would it?. A number of options were discarded fairly early on. Among them appear to have been another track through the station to go below Twentywell Lane and to join the loop. We can forget that
However points splitting off the westbound track immediately after the Twentywell Lane overbridge would, on paper, be able to join the extended chord with another set of points to provide enough length for a westbound passenger train. Except the loop is on a rising gradient to go into Dore tunnel and is canted away from that westbound track to take the sharp curve. I went through all that at the time of the 2016 public inquiry.
If the new points off the westbound track were positioned further west where the loop track was flat and level I'm not sure there'd be enough length in the loop to hold a 6 car train. That wouldn't effect the effective length for freight trains passing between the two lines.
However resolving issues east of Sheffield need far more attention.
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