The government has talked down claims its plan for the A14 would lead to breaches of air pollution limits.
The Campaign for Better Transport said the proposals, which include creating a toll road between Huntingdon and Cambridge, would "seriously worsen" air quality for people living nearby.
But a Department for Transport spokesman said: "The proposed changes to the A14 will move long-distance traffic away from Huntingdon and help to improve air quality there, not make it worse.
"The government understands the impact a national road project like the A14 can have on air quality, and that is why a full environmental assessment will be completed before any work happens."
More top news
Mother, whose son was murdered after being groomed online, warns of dangers of the internet
Turning cloudy and becoming windier later. Patchy rain overnight.
A man's been given an 18 week suspended prison sentence after his three dogs died in a hot car in Peterborough.