Controversial bridges designed to guide bats over the Northern Distributor Road and protect them from traffic do not work, a BBC investigation has found.
When the £205m road was built, 12 bat crossing points were included, including seven bat gantries, two green bridges, two dark corridors and an underpass.
The bat gantries, which each cost £175,000, feature wire mesh strung high over the carriageway between two poles.
But according to the BBC, a report on the first year of the NDR, which was renamed the Broadland Northway, has found none the bridges were effective.
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Surveys carried out during summer of 2018 found more than 40pc of bats were crossing the road at unsafe heights - a proportion experts considered unsustainable for local populations.
And only 49pc of bats were flying close enough to the bridges to be considered to be using them.
According to national guidance, at least 90pc of bats should be flying at a safe height within five metres (16ft) of the structure.
Dr Anna Berthinussen, a bat ecologist, told the BBC it was likely Norfolk County Council's efforts to mitigate the impact of the road had failed.
She said: "The evidence in the report suggests that actually no, these structures are not effective, they're not meeting their purpose," she said.
"I think it's quite striking how few bats there are at any of the crossing points. At one of the bat gantries there weren't any bats recorded at all. At the others, just a handful of bats per survey, which is really worrying."
Dr Berthinussen said the lack of bats at the crossing points was "almost certainly" down to the impact of the road which may have driven bats away from the area.
But the council defended the bridges, saying it was still "early days" when it came to gauging their success.
Martin Wilby, council member for road and infrastructure, said: "I've seen the report. And I've seen that numbers of the bats have been using the bridges across the NDR," he said.
"We should monitor them and if they don't work over a period of time, fine, we'll accept that - but at this present time it's very early days."
? The full report is on BBC Inside Out East at 7.30pm tonight (January 27).
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