Bend it, just a little bit

In my blog You want to go how fast? (posted 9 May 2011) I commented on the influence that the maximum speed that the track is designed to accommodate has on the environmental impact of the track way:

“The maximum running speed specification influences the track geometry and to support 400 kph HS2 Ltd has specified a minimum curve radius of 8,200 metres. This dictates that the route must generally follow a straight-line path, with only very shallow curves. This inherent inflexibility makes it problematic to divert the route around sensitive areas, which may be natural environments that should be preserved, sites of cultural heritage or just places where people live.”

One of the documents that was published by the Department for Transport on the morning of the Transport Secretary’s Commons statement contains a very good illustration of how reducing the design speed allows more scope to “wriggle” around environmentally-sensitive areas, so I thought that this provided a good opportunity to revisit this subject. It is an added bonus, as far as I am concerned, that the example refers to my own dear parish of Cubbington and the fate of South Cubbington Wood, which long-standing readers of this blog will know HS2 Ltd seems hell bent on destroying.

The document to which I refer is Review of HS2 London to West Midlands route selection and speed (here). This document considers a number of facets of the discussion about design speed, including looking at alternative route corridors, but on page 43 reviews the particular problem of whether reducing the design speed will allow scope to avoid driving the track straight through the ancient woodland of South Cubbington Wood.

The outcome of the study is shown on a map on page 44 of the HS2 Ltd document, a section of which is reproduced below.

Lower speed alternatives at Cubbington (source: HS2 Ltd)

The straight line through the Wood is shown in two banded colours: blue and orange. Blue indicates that this route was the one offered for consultation and orange indicates that it remains the preferred route.

The green line indicates a diversion avoiding the Wood that is possible if the design speed is reduced to 225 mph (360 kph) and the mauve line represents a relaxation in design speed to 186 mph (300 kph); this lower figure is the design speed for HS1.

The green and mauve lines appear to be taking the same line past Cubbington, but the text of the report indicates that the two paths are different. Paradoxically the higher speed design moves the line further from the Wood than the lower speed mauve line, by about 50 metres, whereas the mauve line can be set to just skirt the Wood. Since any move away from the Wood moves the track closer to Cubbington village, just skirting the Wood is the better option.

So this work by HS2 Ltd does illustrate that a slower speed design is more flexible and more able to be moved away from environmentally sensitive areas. However, the proximity to the village of Cubbington to the Wood means that any move away from the Wood in this direction is a move closer to the edge of the village, which has the potential to increase the impacts of HS2 on the population of around 4,000. The move appears to have a similar effect on the residents of nearby Offchurch. In the light of this impact on people the report concludes, rightly I would suggest, that the option of bending the route around South Cubbington Wood is not viable.

I would stress though that just because a lower speed design yields no benefits to the Cubbington area, because of the relative positions of Cubbington, Offchurch and South Cubbington Wood, there surely remain many locations along the route where the flexibility offered by a reduced design speed could offer benefits.

In my next blogI will look at the alternative “solution” that HS2 Ltd has come up with to “save” South Cubbington Wood.

Acknowledgement: The Ordinance Survey mapping upon which the HS2 Ltd route design is overlaid has been reproduced in accordance with the principles of fair dealing as set out in the Copyright, Designs and Patents Act 1988.  On this basis, this mapping is:

Reproduced by permission of Ordnance Survey on behalf of HMSO.

© Crown Copyright. All rights reserved.

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