Plans aimed at tackling congestion on the A14 could leave the government in breach of legal limits for air pollution, a campaign group has warned.
Westminster's £1.5 billion proposals for the stretch between Cambridge and Huntingdon include widening parts of the carriageway and a 12-mile toll road.
But the Campaign for Better Transport is warning the scheme would not only significantly worsen air pollution across a wide area - it could actually push a number of locations above current EU legal limits.
Sian Berry, the CBT's roads and sustainable transport campaigner, said: "It would be far more cost effective and sensible to look at ways of reducing traffic levels to help solve congestion more permanently and sustainably without breaking the law and damaging public health."
The government's consultation on the project has recently closed and an announcement on the preferred route is due later this year.