The cost of the Long Stratton bypass has increased by almost £9m, with delays, inflation and the war in Ukraine pushing up the bill.
The planning application for the road, which is linked to the construction of 1,800 new homes in the area, has been held up partly due to the issue around nutrient neutrality, which has prevented councils from approving plans for homes.
Council bosses have confirmed that delay, coupled with inflation and the war in Ukraine pushing up construction costs means the bill for the road has gone up from £37.4m to £46.2m.
The Department for Transport last year pledged £26.2m towards the £37.4m cost of the two-and-a-half mile A140 single carriageway bypass.
But Norfolk County Council now faces having to find other sources of funding to close the gap.
Martin Wilby, cabinet member for highways, infrastructure and transport, said: “Delivery of the long-awaited and much needed Long Stratton Bypass remains a key infrastructure priority for Norfolk County Council, which will deliver jobs and important economic growth across our whole region and make a real difference to people’s lives, particularly for residents in the town itself.
“The issues we face are not unique to our county. The impact of planning delays and inflation cost pressures are being felt across the whole country and beyond, particularly in the construction sector and are broadly in line with the increases we have seen elsewhere.
“We remain fully committed to overcoming these obstacles and are seeking to put ourselves in the strongest position possible to move forward at pace as soon as we are able."
A report will go before Conservative-controlled County Hall's cabinet next month, where councillors will be asked to delegate authority to allow side road orders and land agreements.
The nutrient neutrality issue means Norfolk councils have been blocked from approving plans for homes in areas within the watersheds of the Broads and River Wensum.
Work is under way to find ways for developers to mitigate for pollution from developments which can harm habitats, following the directive from Natural England.
But council bosses still hope bypass building work can start in early 2024, with the new road open by the end of 2025.
Two months ago, the county council revealed the cost to build the controversial Norwich Western Link had gone up by more than £50m to £251m.
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