The preferred route for the Oxford to Cambridge Expressway has been announced.
The corridor will be "broadly aligned" with the proposed East-West rail route from Abingdon to south Milton Keynes via Winslow. It is yet to be decided whether the route will pass west or east of Oxford.
The government said the road will create vital jobs, skills and housing.
A local wildlife trust said it is "profoundly concerned" about the route.
The expressway is expected to take up to 40 minutes off the journey time between the A34 south of Oxford and the M1.
The Department for Transport put forward three possible options for the expressway - A, B or C - and "after detailed scrutiny and review by Highways England" corridor B was selected.
"Corridor B was judged to offer greater benefits to the region - outperforming the other options by providing better links to jobs, education, leisure and health services," the government department said.
Estelle Bailey, chief executive of the Berks, Bucks and Oxon Wildlife Trust said: "In our opinion corridor B is the worst of the three options.
"The potential impact on biodiversity of corridor B is so serious that the route should have been discounted entirely.
"The only way to avoid exceptionally serious impacts on biodiversity would be to develop a road route that is so convoluted that it would fail to qualify as an expressway."
A full public consultation on the proposed route is expected to take place next year.