A final decision has not been made about turning the final section of the A11 into a dual carriageway, following a parliamentary debate on the scheme.
The road, which passes through Norfolk, Suffolk and Cambridgeshire, is a key link connecting Norwich to London.
Conservative West Suffolk MP Matthew Hancock had called for the debate, which was held on Tuesday.
After hearing from Norfolk and Suffolk MPs, roads minister Mike Penning said he was impressed by the case.
He said no decision could be taken about whether to turn the final stretch of the A11 into a dual carriageway until the autumn.
But he added: "The business argument is there."
Mr Hancock had told the parliamentary hearing that the economic case for the project was "compelling".
"Consultants working for the Highways Agency estimate that for £134m cost, the project will generate over £19m in indirect taxes, and economic benefits of over £550m for consumers, and £1.1bn for businesses.
"So on the government's own figures, benefits are over 20 times the cost. That is an astonishing figure."
He said a Highways Agency report found that there would be productivity benefits in Norfolk, Suffolk and Cambridgeshire, concentrated on Thetford, Norwich and Great Yarmouth.
Other MPs speaking in favour of the project included Elizabeth Truss (Con, South West Norfolk), Ben Gummer (Con, Ipswich), Simon Wright (Lib Dem, Norwich South) and Peter Aldous (Con, Waveney).
William Bain MP, Labour's shadow transport minister, told the hearing that he supported the case made for the scheme.
"Increased business confidence, a better investment climate, and bringing together the communities of Norfolk and Suffolk are just some of the tangible benefits that would emerge from the dualling."