It took more than three decades to get approved, two years to complete, and cost more than £100m.

The final 9.1 mile stretch of the A11 to be dualled finally opened on December 12 last year to a celebratory fanfare and promises of 'opening Norfolk for business'.

Economic impact studies – completed before the project was approved – stated the work would save more than five times as much (£557m over 60 years) as it cost.

There were also promises of an 'immediate boost to the confidence of local businesses and residents'.

But six months on, how much of an impact has the development had?

The initial signs are positive. Businesses say they have benefited from shorter journey times and increased access.

For residents, the route to London and Cambridge has been opened up, while tailbacks around Elveden and Thetford have been largely curtailed.

For the Highways Agency, which led the project, it is too early to draw firm conclusions.

But Brian Pitkin, Highways England project manager, said early indications were encouraging.

'Anecdotally, congestion seems to have reduced and the improved road is performing well from a safety point of view too,' he said.

'Like all our road upgrades, the A11 will be the subject of an independent evaluation when it has been open for a year.'

Minor works have been carried out since the opening, including maintenance of the Thetford Sainsbury's roundabout, which was the site of a spate of five crashes in the months after the opening.

Mr Pitkin said work was continuing.

'Since December, we've been busy completing the landscaping and other minor finishing works.

'We now have some further minor amendments to carry out at the Thetford roundabout and at the layby near the Elveden Memorial, which we hope to complete during the summer.

'We are also reviewing whether we can further improve traffic flow at the A11 westbound approach to the Fiveways roundabout.

'If we do carry out these improvement works, it will be later in the summer.

'Following this, we should be able to move our last workers out of the area,' he said.

Mr Pitkin added that the total cost of the project is expected to come in at £104.5m, having been budgeted at £105m.

Norfolk County Council, another of the project's major stakeholders, has had a keen eye on the road's impact.

David Dukes, economic development manager, said the improved road had given the county council more 'credibility' when selling Norfolk to businesses and investors.

'Personally, I feel more confident promoting Norfolk as a well-connected county now to potential investors.

'It's one thing to tell people we are well-connected, but when they used to come up on that road and sit in 40 minutes of traffic at Elveden, it made it harder to sell,' he said.

While businesses outside the county are keener to invest, existing sights and attractions have also felt the benefit with the widening of the net of potential visitors, according to Mr Dukes.

'People will generally travel up to 90 minutes for a day trip, that's the rule of thumb.

'The road opening has expanded our reach to an extra 500,000 people for some places, due to Cambridge being within striking distance.

'Bewilderwood is doing fantastically, the Broads is having another great year, and I know Banham Zoo has plans to capitalise on the extra potential there,' he said.

Has the dualling of the A11 boosted your business? Email andrew.fitchett@archant.co.uk