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
A jilted boyfriend has been found guilty of plotting to "horrifically disfigure" his ex-girlfriend by having her doused in acid.
After a bright start to the day, sharp showers will develop this afternoon
Cool northwesterly winds will bring further showers during the next few days.