The dualling of part of the A47 in Norfolk - and whether the government acted lawfully in allowing that to happen - has taken centre stage in a courtroom battle which will decide the fate of the projects.
Whether three major A47 schemes will go ahead is in the hands of three judges at the Court of Appeal, after a legal challenge launched by environmental campaigner Dr Andrew Boswell.
The former Green city and county councillor saw his High Court challenge over the legality of government decisions around three schemes - dualling between Blofield and North Burlingham and Easton to North Tuddenham, plus the revamp of Thickthorn junction - dismissed by the High Court last year.
But he won the right to take the matter to the Court of Appeal, where his lawyers today argued the government acted unlawfully in approving the schemes.
David Wolfe KC, representing Dr Boswell, said transport secretaries had not properly assessed the cumulative carbon impact of the three A47 schemes against government carbon budgets as the country aims to reach net zero by 2050.
During the morning session at the hearing in the London court, Mr Wolfe said there had been "a failure" by the government to comply with legal requirements under the Climate Change Act and the Planning Act.
READ MORE: Norfolk A47 legal battle backed by presenter Chris Packham
He said the government had made calculations about carbon emissions, but said: "What is not done, and this is the fatal step, is to compare the cumulative assessment with the national carbon budgets and then to factor that into the question of whether development consent should be granted."
However, James Strachan, KC, representing the government, said it was wrong to suggest the secretary of state had "ducked" the issue.
He said their decision had been based on an assessment of the impact of all projects on a national, not local, scale and that it would have been "irrational" to have done anything else.
The hearing continues this afternoon.
Afterwards, the judgment of the three judges - Lord Justice Jackson, Lord Justice Dingemans and Lord Justice Henderson's - will determine whether work on the schemes, which has been on hold because of the legal fight, can go ahead or not.
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