The Cockrow Bridge, a pioneering wildlife crossing over the A3 motorway in Surrey, is set to open in the coming weeks. This 'green bridge' connects two lowland heath nature reserves, providing a safe passage for animals such as adders, sand lizards, roe deer, and foxes, and aims to restore biodiversity in the area.
Addressing Habitat Fragmentation
James Herd, director of reserves management at Surrey Wildlife Trust, has witnessed a decline in wildlife over the past decade. He attributes this to the A3, a major arterial road that splits the Wisley and Ockham commons. 'It has fragmented the habitat, disconnected the ecological permeability of the site,' Herd explains. 'Species on this side can't get to that side because there's six lanes of tarmac and vehicles doing 70mph in the way.'
The £317m M25 improvement scheme, which widened the A3 at the Wisley interchange, further exacerbated the problem. However, National Highways constructed the Cockrow Bridge to mitigate the impact on local wildlife.
Design and Benefits
The bridge is a floating patch of nature reserve, transplanted with heathland vegetation from both sides. Heather, sand piles, and logs provide habitat for insects, reptiles, and birds. 'They can feed here, get cover, they can bask, they can breed,' says Herd. Ground-nesting birds like nightjars, woodlarks, and Dartford warblers are expected to benefit.
Although not officially open, wildlife has already been spotted using the crossing, including foxes, roe deer, and adders. Insects are also a key focus, as they underpin the heathland ecosystem through pollination and decomposition.
UK Lags Behind
Cockrow Bridge is one of the few green bridges in the UK. Ben Hewlett, senior biodiversity adviser at National Highways, notes that the US has over 1,000 animal crossings, while the Netherlands has built about 80 green bridges since 1988. 'We're way behind if you compare us to continental Europe and America and Canada,' he says.
Dr Silviu Petrovan, an assistant research professor at Cambridge University's zoology department, emphasises that Britain is 'one of the most fragmented countries in the world' due to its dense road network. Green bridges are crucial for helping biodiversity remain intact by allowing populations to recolonise after disturbances.
Cost and Future Potential
The Cockrow Bridge cost £3.7m, just over 1% of the overall project cost. Herd believes that dedicating 1% to 3% of road scheme budgets to greening elements could unlock nature recovery. 'Because we're in a nature crisis... unless we act pretty damn swiftly, we'll hit a tipping point where we might be facing ecosystem collapse,' he warns.
National Highways is pushing for more green bridges in future projects, despite the lack of a Treasury methodology to value habitat connectivity. Hewlett concludes, 'If we want to be serious about nature restoration in the country, we have to think about it.'
