Tuesday, 27 May 2014

Heading West

Development of Eden Valley Line - By Ben Yates

Kirkby Stephen East Junction - Stainmore route to the left and the Eden Valley line on the right
  Appleby (latterly Appleby East) was opened in 1862, 14 years before the Midland Railway rolled into town under the duress of Parliament with the railway they didn't want to build - sorry S&C fans, but it’s true, and this makes me wonder if the locals really rang the church bells to celebrate parliamentary approval of the railway coming to town in 1866, when they had an operational line 4 years previously. The Midland station was a stone’s throw across the Schoolyard, but critically was at a higher elevation by some 40 feet, just 200 yards apart. The 2 lines were joined with a north facing junction on the Midland, and a south facing junction on the EVR north of Appleby East. This made the line useful as a diversionary route to the northern half of the S&C, and there are records of the prestigious Thames Clyde Express (behind a Jubilee) having been diverted over
the EVR, so with Class 40s having run to Warcop it can be assumed the EVR was
built to higher loadings than Bouch’s bridges on Stainmore. The link remains to
the day despite the closure of the last section to Warcop, and is still used as an occasional refuge for special trains allowing service trains to pass. The gradient is around 1 in 77, which with a reverse curve presents a challenge to get a train started.
An overall view looking down at Appleby East, to the
left, and the Midland route to the right
  This brings us onto track-laying, and the process of how to go about capturing this in the sim. The starting point is to take the gradient profile and blow it up as large
as possible – this one is done to A3. After checking for copier distortion, work out the distance of each section to the metre. I then check this by measuring the whole length of the section and checking against the cumulative lengths of each gradient. This has usually been within 2-3% accuracy, and individual lengths are adjusted accordingly. In scientific terms, there is bound to be a significant margin for error when dealing with conversions of 1mm = 160m, but the method seems to work pretty accurately in practice.

To get a match between the profile and the DEM, it is necessary to find a known point of altitude of the railway. This is best done by finding an OS Map contour crossing the line where the line is level with the surround terrain. This method can be used to check periodically as track is laid.

The track is laid with easements, which allow use of superelevation to add cant to the track on curves. Easements are the gradual increase in radius of a curve, which gives a smooth transition to the correct radius. The tool in TS13 is, unfortunately, a swine to use and impossible to lay track under the ground, so large parts of the line have to be laid conventionally, and the terrain formed
to allow the track to be relaid with easements. This is all rather time consuming, but the end result is worth it. Another limitation (though sometimes ignored) is that applying superelevation to junctions means the don’t render properly and provide an awful ride from the cab. I make sure the easement section ends before crossovers to avoid this. 
A super-elevated curve just west of Kirkby Stephen, on the Stainmore line
  Appleby was something of a challenge. The key thing was to get the S&C trackwork over the EVR (now the S&C bridge over the A66T) at the correct height for the overbridge, and alos to match the road bridge that goes under the platform. Unfortunately there are 2 changes of gradient on the S&C between there and Appleby Station – level, climbing 1 in 200, then 1 in 400 and it is
impossible to get an accurate measurement from the tiny Ian Allen gradient book. Trial and error matched the track with both bridges (a good hour’s work!) which allowed the joining line to be worked out.

A further complication was the complicated trackwork at Appleby North yard, which includes a double slip – notoriously hard to render correctly, and impossible to do so when using correct track spacing for the 6 foot as we do (the observant of you may have noticed that default tracks have a wider spacing, presumably down to this). To solve this, tracks are laid singly and offset at a
slightly wider spacing, which did the trick. Once the junctions are laid at each end of the link, a piece of track was laid and manipulated to establish the ruling gradient of 1 in 77 (I’ve seen 1in 80 quoted) and after much fiddling I got both lines to join. I’m not totally happy with how the curves match in radius, so there may be some further work to do on this. The junction was singled around 1959, but I wanted to include the full trackwork to reflect the line at its operational peak.

The junction at Appleby
There’s still a turntable to install – it appears on the maps so I assume it lasted until the end of steam – answers on another postcard.

1 comment:

  1. Ben, I have many double slips with 6ft track spacing. Perhaps your track rule minimum radius needs tweaking?