The A413 Small Dean Viaduct

This page presents information about the proposed HS2 viaduct at Small Dean, and the tunnel alternative. For our web page on noise mitigation for the A413 Wendover Bypass please click here.

When you have reviewed the information on this page, please click here to take our short survey.


In their House of Commons Select Committee presentations HS2 said that they would try and make the A413 Small Dean Viaduct look attractive, and with its status as a “Key Design Element” is subject to the overall HS2 Design objectives to make the resulting installation “something that we can all be proud of”.

As shown at the public meeting on 5th July, what the Major Works Construction Contractors (Eiffage Kier) have come up with is something a bit different, and considered by the audience as monstrous and inappropriate in the Chilterns AONB. Eiffage Kier evaluated various options, and the resulting massive steel and concrete design is the best that they can do within the scope currently dictated by HS2 Ltd.

Small Dean Viaduct

The Viaduct Design

The viaduct design is difficult due to a number of requirements imposed by HS2. Firstly, the track curves slightly as it passes over the A413 just south of the Wendover bypass. To cope with the sideways forces from passing trains 11 metres above the ground, the piers need to be very strong to stop the track flexing. This introduces two options currently denied by HS2. One solution would be to have a permanent speed reduction from the 400 kilometre/hour specification, or alternatively to straighten the line which has been rejected due to the time needed for additional land acquisition at Rocky Lane. Secondly, as the line crosses the A413 at a shallow angle the viaduct span needs to be about 60 metres long to avoid re-engineering of the A413 as a dual carriageway with a pier in the central reservation. The massive scale of the spans, and girth of the piers required to support them could be elegant if seen at a distance, but actually cause the structure to appear monstrous due to the limited pier height.

Small Dean Viaduct

Design variants of all-steel, all concrete, and the proposed steel and concrete option were reviewed including cost and A413 construction traffic movement considerations. The resulting best case solution has been presented, with the HS2 Chilterns AONB Review Group and AVDC as the local planning authority having very little influence. This was suggested as being limited to the eventual “finish” of the construction, such as the colour that the steel might be painted.

Having undertaken the initial Design work, the contractors submitted their costings to HS2 and these were rejected as being well in excess of the expected budget, with the companies being told to review their designs and costs, which caused the slip in the start date to June 2019.

A Mined Tunnel

Since the outset of the HS2 project in 2010, Wendover has sought a tunnelled approach locally while the line passes through the AONB; to reduce the noise and visual impact to protect the village for future generations. Having rejected continuous bored tunnelling from the M25, the alternative “mined tunnel” approach between Rocky Lane and North Wendover has been reviewed as feasible by HS2, and recent cost evaluation by Michael Byng (of mbpc Infrastructure) has shown considerable savings compared to the current Small Dean Viaduct, Small Dean North Embankment, and Wendover Green Tunnel approach. Based on 4th quarter 2015 prices and using the methodology in "Rail Method of Measurement - Volume 1 - Cost Planning", the mined tunnel would cost £231m, compared with a cost of £557m for the viaducts etc. included in the HS2 Approved Scheme Estimate, a saving of £326m.

Small Dean Viaduct

The Small Dean North Embankment is not considered as an HS2 “Key Design Element”, and so is not being widely presented. It runs for 900 metres alongside the Wendover Bypass between the south roundabout and Bacombe Lane. With height up to 14 meters (to the track level) this results in the need for significant trackside noise barriers rising a further 6m to mitigate the uninterrupted “line of sight” noise impact on St Mary’s Church and the Chiltern Way Academy school. These visual and noise effects from the embankment would be removed by putting the track underground.

The “mined tunnel” also addresses the issues with the Coombe Hill aquifer, which is expected to be massively impacted by the excavations needed for the Green Tunnel and North Cutting.

Adopting the “mined tunnel” would enable HS2 to meet their requirements to keep the track on the route defined in the legislation, reduce the costs, and protect Wendover and the AONB for future generations. The contractors are aware of the tunnel benefits, but have been inhibited from detailed evaluation by a policy directive from HS2 in favour of the viaduct.

Lord Adonis summed up that policy in November 2017 in evidence to the Treasury Commmittee, suggesting that the tunnels were already too long; “I think that Buckinghamshire is going to fall in love with HS2 when it is developed. This is going to act as a huge spur to new investment and people wanting to move out of London, whereas the Chilterns will be starved of this investment because people will not see the beauty of the Chilterns from the train”.


This survey seeks to gain objective evidence from Wendover as to whether HS2 should change their policy in the Local and National interest.

Can we now seek your opinion on various points, so that we can accurately represent local interests back to the Government.

Please click here to take our short survey.

Wendover HS2