Millions more will have to be borrowed to speed up the construction of the Long Stratton bypass - because developers of a connected housing scheme are not due to make their contribution for another four years.
The government announced in 2021 that it would give £26.2m towards the cost of the two-and-a-half mile A140 bypass, only for the bill to subsequently rise from £37.4m to £46.2m.
The Greater Norwich Growth Board - a partnership of Norfolk, Norwich, South Norfolk and Broadland councils - had already agreed to provide £10m from a pooled fund of a tax on developers.
A further £6m still needs to be identified, but the developers of a 1,800-home scheme linked to the bypass, which secured planning permission last month, are due to give £4.5m.
However, council officers warned the first developer payment is not due until autumn 2027 - and Norfolk County Council wants to get work on the bypass started in spring next year.
So, the Greater Norwich Growth Board agreed at a meeting on Wednesday (September 27) to lend South Norfolk Council £4.5m.
The committee is able, through the City Deal awarded in 2013, to borrow money from the Public Works Loan Board at lower-than-normal rates.
That will allow the work to start years before the developer has to make its payments.
READ MORE: Archaeologists survey Long Stratton A140 bypass route
Officers acknowledged it will mean South Norfolk Council will have to pay nearly £600,000 a year for each of the next 10 years in repayments and interest, although the developer repayments will go towards that.
South Norfolk Council deputy leader Daniel Elmer said: "The campaign for a bypass for Long Stratton can be dated all the way back to the 1920s.
"It is a very significant moment, in terms of improving infrastructure between Norwich, Diss and beyond and unlocking another 1,500 homes."
County council bosses said they hope the road can be built in 18 months, with the scheme open to traffic by the end of 2025.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here