More than £7m could be spent on preparation and planning for the Norwich Western Link.
Conservative-controlled Norfolk County Council's cabinet announced its preferred route for the road, which would connect the Northern Distributor Road to the A47, last summer.
At a meeting next month, they will be asked to approve the approach which would lead to a contractor being appointed to build the £153m project.
And the documents the council will consider reveal, even though the road has not got planning permission or funding in place, it is estimated the development costs will be more than £4m.
That includes procurement of the construction contract, design, the cost of statutory processes and the outline business case.
The council's budget, to be agreed next month, has set aside £3m towards the costs.
On top of that, the council is also likely to need to spend just under £3m to acquire land for the scheme in 2020/21.
And there are likely to be extra costs, as that figure does not include claims which will be forthcoming by landowners making claims under the Land Compensation Act.
Martin Wilby, cabinet member for highways and infrastructure, said: "We've had initial discussions with several potential bidders and are expecting a healthy level of interest in the contract.
"The procurement approach proposed requires the successful contractor to develop and take responsibility for the detailed design and construction of the project.
"This reduces the risk of changes needing to be made to the design at a later stage and gives more opportunity for bidders to suggest innovative ideas, helping to keep costs down and getting the best overall result for Norfolk."
Councillors have selected a 3.9-mile route from the A1067, near the NDR, travelling halfway between Weston Longville and Ringland.
It would link to the A47 at a new junction at Wood Lane near Honingham, with a 720-metre-long viaduct over the River Wensum.
The link has been backed by the Norfolk and Norwich University Hospital, Norwich Airport, fire chiefs and bus bosses.
But it is opposed by the Wensum Valley Alliance, the Green Party, owners of woodland on the route and the Labour group at County Hall.
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