Why is it needed?
Sheephouse Wood is part of a wider landscape including Sites of Special Scientific Interest (SSSI), ancient woodlands, pastures and hedgerows known as Bernwood Forest which is situated between Bicester and Aylesbury. This area is home to 13 species of bat, including the Europe’s most northerly known population of Bechstein’s bat.
In the late 2000s and early 2010s, detailed planning was carried out for the route of HS2 – Britain's new high-speed railway – between London and the West Midlands. After sifting through the options, the partially disused railway corridor through Calvert was identified as offering the best balance between journey times, cost, engineering feasibility and environmental impacts.
However, to build the railway, HS2 must be able to satisfy environmental legislation put in place to protect species such as bats. Any proposed solution (in this case, a 900m-long structure) must also satisfy the requirements of the local planning system, as well as meeting safety and operational regulations for HS2’s high-speed and high-frequency trains.
The original proposal was to cover the two tracks needed for HS2 but over time the structure was widened to accommodate a further two tracks to serve East West Rail (EWR), doubling the size and increasing the engineering complexity of the structure. As we set out below, this is a significant undertaking.
What is it?
The 900m-long structure will cover the railway as it passes between Sheephouse Wood SSSI and a landfill site near Calvert in Buckinghamshire. In this area, HS2 follows the route of the former Great Central Railway corridor, which was closed to passenger traffic in the 1960s.
The northern portal is formed by a landscaped ‘green bridge’ which also carries a footpath across the railway while the southern portal incorporates a drainage culvert and footpath under the railway.
Construction of the foundations and base slab are currently underway. The superstructure will be made of a high-performance weathering steel mesh supported by concrete arches.
As well as HS2 services, the structure was expanded to create space to reinstate the freight line to the nearby FCC waste treatment plant and make it possible to upgrade to double track in the future if East-West Rail (EWR) passenger services are extended to Aylesbury.
Which legal test did HS2 need to meet?
All bat species and their roosts are legally protected, by both domestic and European legislation. This includes the Wildlife and Countryside Act 1981, the Conservation of Habitats and Species Regulations 2017 and the International Convention on the Conservation of European Wildlife and Natural Habitats.
This means that wherever there are known populations, evidence needs to be provided to Natural England to show that the railway won’t harm what’s known as their ‘favourable conservation status’ – to satisfy protected species licencing requirements.
For more common species, this could include simpler mitigation measures – such as new habitat planting to help increase their foraging range, or bat boxes to provide more places for roosting.
At Sheephouse Wood, the fact that the Bechstein’s are a small colony at the northern edge of their range meant that complete separation of the bats from HS2 construction works and the eventual passing trains was needed to maintain their favourable conservation status in the long-term.
Read more about Natural England’s wider role in licencing for work relating to HS2.
How long has it been planned?
The need for the structure was identified by HS2 Ltd more than 10 years ago, following extensive surveying of bat populations by our own ecologists.
The requirement was highlighted in the 2013 Environmental Statement before the introduction of a hybrid bill into Parliament which eventually led to the High Speed Rail (London - West Midlands) Act 2017. Detailed design began with the appointment of EKFB – a joint-venture made up of Eiffage, Kier, Ferrovial and BAM Nuttall – our main works contractor for this area, in 2017.
Which other options did HS2 consider?
In 2021, a ‘first principles’ review was undertaken by the Department for Transport, DEFRA and Natural England, but did not identify any better solution that was able to both fulfil the requirements of the relevant legislation relating to species protection whilst also reducing cost.
The most feasible engineering options were also subject to an additional independent design review by the consultants Arup, which concluded that the solution now being taken forward provided the best balance of value for money and risk mitigation, from the four viable options that were shortlisted.
Choosing any of the other options would have opened-up the risk of legal challenge, delay and subsequent extra cost.
Options considered included a bored tunnel beneath this area, a shallower ‘cut and cover’ tunnel and rerouting the railway away from the wood altogether. Consideration was even given to permanently slowing down trains as they run past the area. Read more about the different options.
Why not move the bats?
Translocation of the bats was one of the options considered (see no.11, above) but Natural England advised that it would be illegal as it would not maintain the favourable conservation status of the population at Bernwood. Bats, especially woodland species, are very specialised and have complex habitat requirements and behavioural ecology throughout their various life cycle stages. The chances of individual bats surviving capture and translocation, let alone the whole populations present at Bernwood, cannot be guaranteed and would not therefore maintain their favourable conservation status.
Why not move the railway away from the bats?
A deep tunnel under the wood or a complete realignment of the railway were considered and would have provided the right level of protection for bats, but they were found to be far more expensive to build. A complete realignment would also have had negative environmental impacts on other areas and local residents.
Did Natural England force HS2 to build it?
It is not Natural England’s role to recommend particular engineering or environmental solutions. HS2 has an obligation to abide by legislation that exists to protect nature. Natural England and HS2 Ltd have a team that works closely together to ensure that this duty is observed, so the rail line can be completed without harming important wildlife.
Natural England was consulted on whether the proposal designed to mitigate the impact of the railway on rare and protected bats was sufficient to comply with environmental law – and they advised that it was.
Not going through this process would have been illegal and opened up the risk of judicial review and all the associated risks of extra cost and delay.
Read more about Natural England’s role.
How much does it cost?
The cost of the structure is determined by the scale and complexity of the engineering and the extensive foundations works required due to running parallel with the Network Rail line as well as the proximity to the adjacent landfill site and the need to avoid taking land from the ancient woodland.
The structure itself is a significant piece of engineering which is required to have a design life of 120 years. It is around 900m long, up to 10m high and will be four tracks wide. It also includes extensive safety requirements to separate the two operating railways and a green bridge built into the north portal.
It must accommodate up to 36 high-speed trains passing through the structure every hour of operation, plus frequent conventional rail traffic. It is designed to enable safe railway operation, be impervious to fire and passively ventilated.
The cost of the structure is c. £95 million (2019 prices).
The above-ground elements (i.e. the cost of the physical barrier between bats and trains) are c. £70 million, with the remainder c. £25m of the cost being additional below-ground civils works required to accommodate the structure (e.g. foundations).
A third of the cost is being contributed by East West Rail given that the structure is being built to accommodate its services in the future (although a decision on whether it will is yet to be taken).
In 2022, some newspaper headlines implied that the cost of the structure was expected to be £40m (2019 prices). This was based on the advertised value of one foundation subcontract and was not the full estimated value of the structure at that point.
More information about cost can be found on the Public Accounts Committee pages of the Parliament website.
How many Bechstein’s bats does it protect?
Natural England estimate that there is a population of around 300 Bechstein’s across the wider Bernwood area, which includes Sheephouse Wood.
HS2 is helping to add to the scientific understanding of this rare species and has been conducting surveys for more than 10 years. This monitoring is ongoing, but during the detailed surveys undertaken in 2022, ecologists working for HS2 trapped (and released) 30 Bechstein’s bats within Sheephouse Wood and identified at least 19 confirmed roosts. This indicates that a good number of the wider population use the wood for roosting and foraging.
Read more about the wider population and Natural England’s proposals to designate the Bernwood areas as a SSSI.
Is it being designed to ensure “zero harm” to bats?
The structure’s design is required to maintain the favourable conservation status of the whole Bernwood population. In practice, this requires almost complete separation of bats from passing trains at this location given the relatively small number of bats and the rarity of the species.
Is this HS2’s only bat structure?
This is the only structure of its kind on HS2.
There was already a railway here. Why is it necessary now – but wasn’t needed in the past?
The old railway through the site was closed to passenger services in the 1960s before the relevant legislation came into force. Since then, it has mostly been used by freight trains delivering rubbish to the landfill site – these slow, infrequent trains are a far smaller risk to bats than frequent high-speed services.
What other consents were needed to build the structure?
Despite the passing of the 2017 Act, HS2 Ltd still had to gain almost 8,500 environmental or planning consents along the 140-mile route from London to the West Midlands.
For Sheephouse Wood, this also included approval from Buckinghamshire Council under Schedule 17 of the HS2 Act for matters relating to the external appearance of the structure. After 4 years of engagement and dozens of meetings, the council failed to grant its consent.
To avoid further delay HS2 Ltd was forced to escalate the case to the Planning Inspector, who determined the planning consent in their favour, allowing construction to begin in 2024. The inspector’s decision can be found here.
HS2 are setting new standards for environmental sustainability, ensuring wildlife protection – and the bat structure is a prime example of that ambition.
There are a number of complex reasons why infrastructure delivery costs in the UK are high, as well as why costs on HS2 have risen. There are few, if any, new railways being built in the world that have to meet the environmental standards of HS2, but other factors such as inflation, design and productivity have also been contributing factors.
Are there any more images of the structure?
The latest images can be found on our media gallery - credit: HS2 Ltd
