Infrastructure Minister Chris Hazzard has given the green light to the Ballynahinch bypass - but only when the money is available.
The scheme, which has been languishing at Stormont for more than a decade, is expected to cost in the region of £35m.
However, estimates of the bill have varied wildly, from £10.8m in 2005 to £40m-£50m in January 2012.
The A24 bypass scheme has been talked about since as early as the 1960s.
Commuters often face chronic congestion in the Co Down town, which lies around halfway between Newcastle and Belfast, every morning and evening. Day-trippers from the city are also hit by the gridlock in the bottleneck town while heading south to Newcastle.
Alliance MLA Kellie Armstrong claimed Mr Hazzard had put too many infrastructure schemes on the long finger and said that certainty was now needed.
"Yet again we have a much needed scheme being progressed and approved, only to be put on the long finger," she added.
"It joins the York Street interchange and Downpatrick distributor bypass on a growing list of schemes where Minister Hazzard is keen for positive headlines that promise but do not deliver.
"The Ballynahinch bypass is much needed and the motorists using the roads every day are feeling increasingly frustrated at the delay in getting started on the ground.
"We need the minister to announce start dates, not make excuses."
A public inquiry was held in January into the proposed scheme, and the inspector reported his findings to the Department in March.
Sinn Fein minister Hazzard, who has now accepted the report's recommendations, said: "I am delighted to announce this key step in the development of the Ballynahinch bypass, which is seeking to address the traffic delays at this bottleneck along the A24, which are familiar to those who travel along this strategic route every day and to the Ballynahinch community.
"Progressing a scheme of this scale represents significant investment for the area.
"The provision of the bypass will improve journey time reliability and road safety for motorists, including freight transport.
"I am personally familiar with the difficulties faced by strategic and local motorists travelling the A24 route and welcome the positive outcome from the inquiry.
"Consultation will now begin with key stakeholders, and in particular landowners, affected by the scheme with a view to minimising the related impacts."
The Department for Infrastructure will now publish the formal environmental statement notice to proceed and the making of the direction order for the scheme.