Liberal Democrat leader Nick Clegg has given a commitment that if he were to win power in the election, he would want to see the last single carriageway section of the A11 - which links Norwich to the M11 - turned into a dual carriageway.
A Labour Party spokesperson told the BBC the party was also committed to the scheme. The Conservative Party said it supported the scheme, but could not guarantee it.
The A11, which passes through Norfolk, Suffolk and Cambridgeshire, is a key link helping to connect Norwich to London.
There has been a long campaign to get rid of the single carriageway in west Suffolk and business leaders have argued it is vital for linking up the transport network of the region.
However, plans for the dual carriageway were put on hold for the 2010 general election.
On a visit to Norwich, Mr Clegg, when asked about his view on the proposed work for the A11, said: "We are committed to it."
"We think a lot of money is wasted on the roads budget by the government. The government has set aside £6.6bn," he said.
"The vast majority of it was earmarked for poorly justified projects. But this [A11 dual carriageway project] is totally justified."
The Conservative leader David Cameron earlier told the BBC, when asked about the A11, said: "The government have had 13 years to deal with the problem and they haven't.
"Everyone knows it needs to be done. Everyone knows we want it to happen. Clearly we have the inspectors' report still to come forward.
"We want to do it. You can't make guarantees in this world but we fully see the case for it and look forward to the inspectors' report and will act on it when we're in government, if we're in government."
The Labour government's Transport Secretary Lord Adonis told the BBC of his support for the scheme.
"Labour is committed to completing the dualling of the A11 with construction beginning this year.
"This will give Norwich the high-quality road connection it needs to promote investment in the city."