Plans to push ahead with the £274m Norwich Western Link will be "disastrous" for Norfolk's wildlife, environmental organisations have said.
Ecologists say owls, bats and badgers will be killed or injured by vehicles on the 3.9-mile road, which would connect the Northern Distributor Road to the A47 west of Norwich.
Norfolk County Council's Conservative-controlled cabinet agreed on Monday to take the necessary steps to submit an application for the road to its own planning committee next year.
The council says the road is needed to cut congestion, reduce rat-running and boost the prosperity of the county, but critics slammed the decision.
The Norfolk Wildlife Trust, the Woodland Trust, Buglife and the Campaign to Protect Rural England (CPRE) are angry at the council's determination to continue with the road.
Mike Jones, Norfolk Wildlife Trust's planning and advocacy manager, said: “Species such as owls, bats and badgers will be condemned to collisions with cars as they continue to use what remains of the landscape they are dependent on for everything.
“The road would be disastrous for Norfolk’s wildlife and would set a dangerous precedent for national decision-making at a time when we must focus on nature’s recovery, not allow its further destruction."
Conservation scientist and bat expert, Dr Charlotte Packman, said her studies had shown the area was home to the largest known barbastelle population in the country.
And Jamie Robins, programme manager for Buglife, said the viaduct over the River Wensum could threaten the river with pollution.
Graham Plant, the council's cabinet member for highways, infrastructure and transport, said the council had conducted its own bat surveys and would provide mitigation.
He said Norfolk Wildlife Trust had not, despite requests, provided the council with the data collected by Dr Packman.
Mr Plant said the scheme includes a surface water drainage scheme and strategy to capture run-off from the road, with no discharges into the River Wensum.
The council has been awarded £213m towards the £274m scheme.
Leaders hope the government will increase that to £251m, but it still leaves the council needing to plug a gap of at least £23m and, potentially, more than £60m.
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