More work will be done to make roundabouts on the Norwich Northern Distributor Road safer, as council bosses conceded a string of lessons must be learned from the scheme.
The budget for the 12.5 mile road, also known as the Broadland Northway, spiralled from the £148.5m estimated in 2013 to £205m.
And council bosses have outlined numerous lessons to be learned from the way the contract was awarded and managed.
Also, a safety audit has shown that the accident rate on the road is high, although the severity of the crashes is low.
Norfolk County Council has already spent £130,000 to make improvements to roundabouts, but will soon make more changes.
Temporary screening, to reduce dazzling, will be put up on the Wroxham Road roundabout and extra chevrons will be added on the approach to that and the North Walsham Road roundabout.
Changes will also be made at the airport roundabout to slow down drivers.
The cost of work and when it will be done, is yet to be revealed.
With the council having awarded a contract for the Great Yarmouth Third River Crossing, they say lessons have been learned from the NDR contract.
The council acknowledges the nature of the contract it had with Balfour Beatty meant the council had borne the costs of design changes during the course of construction.
But Martin Wilby, cabinet member for highways and infrastructure, said that sort of contract had been the right approach at the time.
He said, even though it had come in over budget, the road was worth it.
He said: "It's absolutely worth it. The benefits of the road are being seen already - cutting congestion, improving access for business and helping the tourism industry.
"We have already put some safety measures in and I'm sure the new recommendations we are going to put in place as soon as possible will improve it further."
But Steve Morphew, leader of the Labour group and chairman of the scrutiny committee which will consider the reports later this month, said: "There is still no explanation why the NDR was allowed to go so far over budget, why it was not noticed until too late, what monitoring systems failed or were absent, and why no politician is taking responsibility."
NDR Crash Statistics
In the 12 months after the full opening of the NDR in April 2018, there were 28 accidents in which people were hurt on the road, a safety audit found.
Two were serious and 26 were slight injuries - but council bosses acknowledge that the accident rate is high for a modern dual carriageway.
However, they say that is "misleading" as most dual carriageways do not have so many roundabouts in such a short stretch of road and the actual severity of accidents is low.
Three quarters of the accidents happened at four roundabouts. Five happened at the airport roundabout (three were people overshooting in the dark and two were loss of control).
Five happened at the North Walsham Road roundabout, seven on the Wroxham Road roundabout and six at Salhouse Road roundabout.
While 10 happened in darkness, the council says it has no plans to put in lighting, given environmental considerations.
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