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
Very warm with sunshine. Chance of thundery showers late morning.
A hot, humid and sunny start before cloud increases as a narrow band of thunderstorms spreads northeast. These clear during the afternoon.
A fine and sunny end to Friday will then be followed by a warm and muggy night. Warm and sunny on Saturday with the risk of a thunderstorm.