A motorway junction and roundabout near Swindon will need an £11.5m upgrade if more homes are built on a site nearby, a report has revealed.
Planning conditions for Wichelstowe development, state the work at junction 16 of the M4 must be completed before the 1,100th home can be occupied.
Without the junction revamp the town would be short of new homes and jobs, Swindon borough council said.
But opponents claim this will bring extra traffic to nearby villages.
'Mass of lanes'
Town councillor Chris Wannell, from nearby Royal Wootton Bassett, said whatever work is done to the junction, bridges in the area will be the pinch points.
"You can't make them [the bridges] wider without major construction and that is not planned," Mr Wannell said.
"What they are planning on doing is to make a mass of lanes on the western side of the junction... making an even bigger car park.
"I don't think they've got enough land to do what they're saying on this plan."
The business case report said the existing layout at junction 16 is unable to cope with current and forecast traffic levels.
Swindon Borough Council said the work is necessary to reduce delays at the junction for the 6,000 vehicles an hour coming off the motorway and crossing the junction between Royal Wootton Basset, Wroughton and west Swindon.
The proposals also include widening the slip roads off the motorway to four lanes in both directions, creating a right turn for Swindon traffic turning on to Hay Lane, and widening the carriageway on the Great Western Way approach.