The completion date for widening part of the Heads of the Valleys road has been pushed back for the second time this year, prompting anger from locals.
Work between Gilwern in Monmouthshire and Brynmawr in Blaenau Gwent began in 2014 and was due to end next month.
In April the Welsh Government said work would run "into 2020", costing an extra £54m, bringing the project to £324m.
On Tuesday it said it was "reviewing the project with a view to complete it at the end of 2020".
It said the latest delay would not have an impact on the overall cost of the scheme.
The news has been met with frustration by some local residents and business owners who say drivers have been cutting through Gilwern rather than using the official diversion when the section of the A465 has been closed on some weekends.
Residents on Maesygwartha Road said cars had been scraped and walls hit by large lorries.
Chris Bromfield, who owns Bromfields Butchers in the village, said people had had enough: "Our road where we live, it's being used as a rat run.
"With these road closures, you're trapped. You can't get out of your house. It's an absolute nightmare.
"There've been walls knocked down, cars damaged. What can we do? You can't blame people for not wanting to take this long diversion - it's probably about 20 minutes, it's right out of the way."
He said he had recently had to lose a member of staff as his takings are down about 75% when the closures are in place.
"If the business can't sustain these road closures then obviously we would have to look at either closing or relocating the business," he said.
"Small businesses just can't sustain this sort of thing. We've had meetings asking for help about putting signs up to let people know that the businesses are open as normal - people are just thinking the road is closed and we're not open and they're not coming up to us."
The work is part of the Welsh Government's £800m upgrade programme for the road to turn the whole route from Monmouthshire to Neath Port Talbot into dual carriageways.
The final phase of the work between Dowlais Top in Merthyr Tydfil and Hirwaun in Rhondda Cynon Taff has not yet started and is due for completion by 2023.
Ministers have described the route as "a crucial artery of our transport network and the principal road link between west Wales and the Midlands" and said safety and journey times will be improved as a result of the work.
A Welsh Government spokesman described the project as "ambitious and challenging", adding: "The Welsh Government and Costain are reviewing the project with a view to complete it at the end of 2020.
"It is expected the eastern half of the project will be completed earlier.
"We remain very grateful to those living and working in the area for their patience while the works are ongoing."