Bosses behind the £178.5m Norwich Northern Distributor Road today warned a cold snap could put paid to their hopes of traffic using the route by this time next year.
Contractors Balfour Beatty, building the 12.5 mile road on behalf of Norfolk County Council are keen to get the road open by December next year.
With the first year of work on the road, due to stretch from the A47 at Postwick to the A1067 Fakenham Road, nearing an end, they say progress is ahead of schedule in many areas.
But they said their opening goal could be hampered if the weather turns, which would set back opening to 2018.
Chris Sedman, project director for Balfour Beatty, said: 'We've done well in the first year, but there are some real challenges ahead - especially if we are going to meet our aspiration of having traffic using the road by this time next year.
'If we can maintain momentum, that's not out of the question, but most of the winter still lies ahead and a prolonged cold snap would be bad news.
'Whatever the weather brings, we know that our work in the months ahead will inevitable affect local people and road users.
'Some communities, such as the Plumsteads and Horsford, probably feel that they have had more than their fair share of disruption, but they have also understood that we have a job to do and that everyone benefits if we finish sooner, rather than later.'
The project is well ahead in terms of earthworks, with 1.2m of the 1.5m cubic metres of bulk excavation completed.
Around five-and-a-half miles of the carriageway has been stabilised and 14,000 tonnes of Tarmac put down, which is also ahead of schedule.
But the main surfacing effort will be next year, with another 149,000 tonnes due to be laid to complete the dual carriageway and side roads.
Storm Angus and a cold start to December delayed the first beams being put on one of the road's seven bridges this month, with Plumstead Road and Buxton Road bridges now due to have beams laid by the end of January.
Ian Taylor, project manager for Norfolk County Council, said: 'When we started last January, if you had offered this amount of progress by the end of the year, we'd have grabbed it with both hands.
'Given that we had so little time between full approval by the government and the start of work on January 4, it is remarkable that we have been able to gear up so quickly and get so much done in the first 12 months.
'Environmental and wildlife featured large in the early days, and we were probably the only people to be thankful of the late cold spell because an early start to the nesting season would have stopped much of the site clearance work - although the lower temperatures also delayed our newt trapping.
'We knew that the weather would continue to have a big part to play. With around two million cubic metres of topsoil stripping and bulk excavation to be carried out, a wet spring and summer would have made life very difficult.
'We had a taste of this at the end of June, when the storms inundated our works and caused a lot of damage, but after that the weather dried up and stayed fine well into the autumn.
'Storm Angus knocked us back, and also the cold snap at the beginning of December, because it was too cold to pour concrete.'
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