David Cameron was given a guided tour of the A11 dualling project at Elveden on Friday.
The Prime Minister spent almost an hour looking round the site with South West Norfolk MP Liz Truss, Highways Agency Chief Executive Graham Dalton and project manager Geoff Chatfield.
Mr Cameron said: It’s hugely satisfying to see this vital piece of infrastructure getting fixed.
“It’s an important promise we made, an important promise that’s been kept.
“We’ve now got proper dual carriageway all the way between London and Norwich and that’s going to be great.
“Lets look at the big picture, which is that we are spending £1.9 billion on improving infrastructure here in East Anglia with more money going into East Anglia actually than anywhere else in the country other than London and the South East.
“It’s a real programme of infrastructure and investment only possible because we have a long term economic plan and because we have made savings elsewhere so we can prioritise the infrastructure that will help to drive our economy.”