A new report into the merits of fully dualling the A47 through Norfolk, Suffolk and Cambridgeshire is to be produced.
Consultants are to be paid to put together a new dossier council leaders believe will strengthen their long-running campaign to get the government to pump millions into dualling the whole of the A47 from Lowestoft to the A1.
Members of the A47 Alliance, made up of councils, business leaders and transport groups, said they wanted to commission the report to look at two main issues.
The value for money - comparing the cost to the benefits - of fully dualling the road will be investigated.
Consultants will also be asked to assess the impact on carbon emissions of dualling now or 10 years from now, compared to doing nothing.
Graham Plant, chairman of the A47 Alliance and cabinet member for highways, transport and infrastructure at Norfolk County Council, said it made sense to keep pressing for the full dualling of the road and to present evidence of the benefits.
He said: "We absolutely know that there are some elements of the road in the countryside which do not have a good benefit-cost ratio. So it's important we present evidence for the full road, to keep that ratio high."
Councils involved in the Alliance, including County Hall, would be asked to contribute towards the £26,000 cost of producing the report.
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It builds on the Just Dual It! campaign, which aims to put pressure on the government to fully dual the A47.
Three A47 schemes in Norfolk - Thickthorn Roundabout, the dualling of the A47 between Blofield and North Burlingham and Easton to North Tuddenham - have been granted consent.
But construction has been delayed pending a legal challenge by former Green county councillor Andrew Boswell over the government's decision to allow the projects.
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