Cost of Dawlish diversion could reach £3.1 billion - NR

Rebuilding the Exeter-Plymouth line via Okehampton would probably mean building a double-track line using the original alignment, and cost £875 million (including a 66% uplift in costs). 

Network Rail says it could be built as a single line with loops, which would reduce the cost by 20%-25%. These loops could be up to 5km (3.12 miles) long.

The NR West of Exeter Route Resilience Study does highlight that Meldon Viaduct could not be used. It says the 165-metre long, 46-metre high structure “is too badly deteriorated for re-use”, adding: “A new structure would be required, adjacent to the existing structure.”

After that, the Meldon Quarry-Bere Alston section is lifted, and would need replacing. NR says that some structures have been removed and the trackbed sold. In some places it has been lost to agriculture, while West Devon Borough Council and an NHS clinic occupy the trackbed at Tavistock. 

NR also claims that a proportion of existing earthworks will be deficient, although Tavistock-Okehampton should be less of a problem as it is built on rock. 

The route is also steep, with a predominant 1-in-75 gradient, although NR points out that banks west of Newton Abbot on the current route are even steeper.

Timings-wise, it suggests a non-stop Exeter-Plymouth journey for a Class 220 Voyager of 53 minutes, against the 49-minute journey via Dawlish. Reversals add “at least a further ten to 14 minutes to through journeys”. It claims the running time penalty is modest, since some sections of line would have higher speeds than the existing route. 

Journey wise, the templates NR suggests include: a regular local service, with through trains diverted when required. Because of the longer journey time, it is assumed that through trains would not routinely use the route, a small proportion of First Great Western and CrossCountry trains may run via Okehampton, so drivers can retain route knowledge, a journey time between Exeter and Plymouth has been assessed at 75 minutes, with a 29-minute journey time between Exeter and Okehampton.

The local journey times assume a Class 165 operating the route. 

NR says that, without flood risk alleviation, the route’s costs are broadly similar to Airdrie to Bathgate. However, the higher number of viaducts and bridges (including Meldon) raises the cost. 

It warns that up to eight miles of track may need raising by up to three metres on higher and wider (or replacement) embankments. Raising the track level through areas of flood risk may cost up to £290m in a ‘worst case scenario’, in addition to the £875m identified for core works.

It adds that an assessment of the current demographics and assumed trip rates found a benefit:cost ratio for a local service of 0.82.

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  • Jim Root - 27/12/2015 19:09

    How does this cost compare with the alternative of a completely new inland route behind Dawlish? The other options like reusing the Exeter - Newton Abbot line via the Teign Valley route seem less attractive as the original route was a single line branch anyway and the major tunnel on the route has collapsed internally.

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