A47 dualling study found fall in vehicles using the road

But council leaders insist that will not stop them lobbying the government to commit to dual all remaining single-carriageway sections of the road between Lowestoft and Peterborough - which would cost £19bn.

Members of the A47 Alliance, made up of councils, business leaders and transport groups, commissioned consultants WSP to look at two main issues around the road - value for money and carbon emissions.

That report has been published, but council officers conceded "unfortunate" timing limited what conclusions could be drawn.

TRAFFIC FLOWS DOWN

Traffic flows from 2022 were compared to 2011 and found the majority across 14 sections of non-dualled road in Norfolk, Suffolk and Cambridgeshire, had gone down.

The A47 Alliance is pushing for full dualling of the road (Image: National Highways)

For instance, afternoon traffic on the eastbound King's Lynn to Swaffham section was down 29pc on 2011 levels, while afternoon traffic on the westbound Acle Straight, heading to Norwich from Great Yarmouth, fell by 23pc.

It meant the number of crashes predicted to reduce through dualling also dropped, although consultants said it would still bring "considerable accident benefits throughout the A47".

The Acle Straight seen from the air

READ MORE: 'Mixed results' over moving snails raises fears over Acle Straight dualling

Consultants said the Covid-19 pandemic, which led to more people working from home, was still having an impact on traffic flows at the time of the study and it was "very difficult" to predict if they would return to previous levels.

They said the study was "high-level" and focussed on possible journey time and accident benefits, rather than other factors, such as wider economic benefits and whether traffic would be rerouted to the A47 after dualling.

Given those "uncertainties and weaknesses", consultants did not undertake a full cost-benefit calculation, saying that would have been "misleading".

CARBON EMISSIONS

The study also looked at what carbon emissions would be produced by full dualling, comparing theoretical opening years of 2025 and 2035.

Consultants said carbon emissions would increase by about 3pc compared to a single carriageway, because of higher traffic speeds, but would decrease in future with more electric vehicles on the road.

The report stated: "The embodied carbon analysis shows the total carbon emissions covering all the segments of A47 is estimated to be over 67,000 tonnes of carbon dioxide emissions for a 2025 construction year.

"If the construction is delayed by 10 years to 2035, there is expected to be a carbon saving of almost 50pc of the carbon impacts estimated for 2025."

David Cumming, strategic transport team manager at Norfolk County Council, said the carbon data would be useful in making the case for full dualling, but acknowledged use of traffic data when Covid-19 effects were still being felt, was "unfortunate".

Graham Plant, Norfolk County Council cabinet member for highways, infrastructure and transport (Image: Norfolk County Council)

DUALLING PLEDGE

Yet Graham Plant, Norfolk County Council cabinet member for highways, infrastructure and transport and chairman of the A47 Alliance, said: "The A47 Alliance will continue to push for the full dualling of the A47, but that does not mean that improvements in the meantime would not be welcome.

"Further improvements are essential to help businesses grow, help residents get around and help our economy thrive.

"We need to keep the A47 at the forefront of government and the Department for Transport's minds for the benefit of future generations."

The county council's Just Dual It! campaign aims 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 -  were granted government consent in 2022.

But construction was delayed pending a legal challenge by former Green county councillor Andrew Boswell over the government's decision to allow the projects.

Dr Andrew Boswell lost his legal challenges over A47 dualling schemes (Image: Dan Grimmer)

Dr Boswell's High Court and Court of Appeal challenges, which argued the government acted unlawfully because it did not consider the cumulative impact of the schemes, was dismissed. He has suggested he could take the matter to the Supreme Court.

'MISGUIDED'

Green county councillor Jamie Osborn said the latest study "knocks the legs out from any argument for dualling".

Green county councillor Jamie Osborn (Image: Submitted)

He said: "Spending hundreds of millions of pounds on dualling the A47 to accommodate more cars seems misguided when in reality there are fewer cars on the A47 than a decade ago. 

“The fact that traffic on the A47 has fallen – in contrast to other parts of the country – knocks the legs out from any argument for dualling. 

“The county council needs to admit the extremely costly dualling project is bad value for money, and needs to focus instead on improving local road networks and public transport."