There are fears plans to restrict access to towns from one of Wales' main roads for a year during its £800m upgrade could "isolate" communities.
Contractors are proposing to shut the Brynmawr roundabout in Blaenau Gwent on the A465 Heads of the Valleys road as they make it a dual carriageway.
It means the main route to a number of towns in the Gwent valleys will be restricted.
The Welsh Government said there was "ongoing discussions" about the work.
The 20-year Heads of the Valleys project is Wales' biggest road building project and the final phase would completely dual the route between Swansea and the Midlands.
Drivers on the A465 currently have to go around a roundabout at Brynmawr - but builders are re-routing the road and creating a motorway-style interchange to alleviate congestion.
But while the upgrade work is being carried out, local residents and politicians fear access to the main artery to and from Brynmawr and the towns of Blaina, Abertillery and Nantyglo will be restricted.
One option was to build a temporary junction but locals say workers have told them that is now not practical.
Instead local politicians say traffic travelling westbound would not be able to get off at Brynmawr. Travelling eastbound you would still be able to get on and off near the town but you would have to follow a diversion.
"Our concerns are about the isolation of the community of Brynmawr," said councillor Lyn Elias, who has met with Welsh Government and contractors Costain.
"For a town to be isolated for 12 months, we are afraid that the business and the community couldn't cope."
The £324m five mile-long (8km) project across the Clydach Gorge between Gilwern in Monmouthshire and Brynmawr started in 2014 and was due to end next month.
But it has been beset by problems and delays and the latest completion date is April 2021.
"When they started doing consultations up here on where the road was going to be built which was 2013-14, on the original statement they said there that there would be no adverse effect on the communities under this scheme," added Mr Elias.
"We think this is a bridge too far.
"There is anger within a certain part of the community because they are saying 'how much longer, how much longer'."
Local MP Nick Smith said there had been a "massive failure" by Costain to engage with local people about the changes, leaving many "surprised and angry".
Businesses are now collecting signatures to form a petition against plans to shut the roundabout.
"For us as a charity, it has financial implications," said Beth Watkins, of the Market Hall Cinema in the centre of Brynmawr.
"Because people are less likely to struggle to get to Brynmawr whichever direction they are coming from and may opt to go to larger multiplex cinemas.
"We are the hub of our community and we have concerns as well of the impact socially for a lot of our customers who use the cinema as a way of alleviating isolation."
If the plans go ahead, the village of Beaufort near Brynmawr could see more traffic as drivers try to get on the Heads of the Valley road at Rassau and off it at Garnylan.
"For the business, it could mean we could close because of the gridlock," warned Melanie Wertheim, one of the three sisters who run the Carini family shop in Beaufort.
A public meeting for people who live in Beaufort is being held on Wednesday.
"It would be absolute chaos through Brynmawr, Beaufort and Tredegar," added Ms Wertheim.
"Everyone in the community is worried. At peak times at the moment, it is dreadful."
A Welsh Government spokesperson said: "We are in ongoing discussions with the local authority and local politicians about the best possible course of action to alleviate the traffic concerns.
"An information campaign will be launched shortly, together with a series of public exhibitions."