New £350,000 bat bridges installed on the recently-dualled stretch of A11 are not working, a study has revealed.
Designed to help bats cross roads, the bridges feature wire mesh strung high over the carriageway between two poles.
The wire mesh is intended to replace hedgerows and trees that have been removed, giving the bat a reference point for sonar, so that they can avoid the road when flying.
The bridges have been heavily criticised over concerns they are ineffective and a waste of money.
Six of the bridges were installed on the new stretch of A11 between Thetford and Barton Mills, after six bat species were detected in the surrounding area before the project started in 2013.
But a study from Anna Berthinussen and John Altringham at the University of Leeds, produced for Defra, reveals that the bridges are not helping bats avoid the road.
The study focused on three bridges and an overbridge on the Elveden bypass section of the road.
It found that most bats 'used' the bridges at unsafe heights, with more than 80pc flying below five metres above the road.
This was in stark contrast to the target of at least 90pc of bats using the bridges as intended, in order for it to be considered effective.
It says: 'We can conclude that neither of the installed bat wire bridges is effective in guiding bats safely over the road.'
A spokesman for the Highways Agency, which ran the A11 dualling project, said it took its 'environmental responsibilities seriously'.
'Bats are an important part of our native wildlife and as a protected species we are legally obliged to protect them. We plan bespoke crossing structures, such as bat wire bridges, when all other options have been discounted.
'The measures on the A11 were modified from previous designs on our network to improve their potential for use by bats and were part of a larger package, including a landscaping programme and artificial bat roosts, intended to support local bat populations,' she said.
Dr Stuart Newson, project manager for Norfolk Bat Survey and senior research ecologist for the British Trust for Ornithology, said bat bridges were being installed without sufficient evidence.
'There haven't been enough studies done to show if the bridges work in particular situations, but the current evidence we do have is that they aren't.
'Decisions on bats need to be guided by more data. We should be investing in studies which will save us money in the long run.
'Overall though, I'd rather see bats being considered than not when these projects take place,' he said.
What do you think of the use of bat bridges? Are they a waste of money? Email andrew.fitchett@archant.co.uk
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