A21 widening scheme considered at public inquiry
Conservationists have warned that plans to widen the A21 would destroy 22 acres of woodland.
A public inquiry will open into the possible upgrading of the road between Pembury and Tonbridge, in west Kent, into to dual carriageway.
Businesses have said the scheme is needed to reduce a bottleneck and government money could be available from 2015.
However, the Woodland Trust said the scheme would damage the environment.
Oliver Newham, from the trust, said: "There are over 1,000 species of fungi in here, 10 species of ladybird, 24 species of bee - I could go on.
"We're talking about a woodland that's been here for 400 years - that's a lot of history to lose."
The section of the A21 under consideration carries more than 35,000 vehicles every day.
The widening scheme would cost £21m.
Jackie Matthias, who is from the West Kent Chamber of Commerce, said: "We in business just can't understand how things can take so long and cost so much.
"It's slightly worrying - you do wonder who is looking at it and scrutinising it."
The inquiry is scheduled to start on 14 May.