The M11 could be widened to four lanes in each direction if a second runway is built at Stansted Airport.
BAA illustration of revised plan for new terminal at Stansted
Plans for new road and rail links from London and Cambridge, needed to serve a larger airport, were unveiled by airport operator BAA on Tuesday.
The M11 motorway would have to be widened between the M25 and the Stansted junction to carry millions of extra passengers.
Expansion plans are opposed by resident groups living near the airport.
Residents fear the plans will ruin the countryside, increase traffic and damage the environment.
To meet the expansion of the airport, BAA announced there will be more trains, with extra carriages, and a second rail tunnel into the airport.
The M11 would be made into an eight-lane motorway at a cost of £324m.
A spokesman for the Stop Stansted Expansion said: "BAA's proposals would lead to an extra million people a week travelling to or from the airport, and the pressure on the road and rail infrastructure would be far greater than at Heathrow today."
But the plans depend on the second runway being given the go-ahead by planners.
In November an attempt by airport bosses to increase flight numbers was blocked because of fears that expansion would add to climate change.
Uttlesford District Council, which covers the airport, blocked plans to extend the existing runway in order to increase plane movements from about 220,000 to more than 260,000 per year.
Councillors turned down the planning application by BAA, citing climate change as one of a number of reasons for refusal.
Environmental campaigners hailed the council's decision as a benchmark, saying it was the first time climate change had been listed as a reason for refusing a planning application.
And residents of villages around the airport, who have mounted a long campaign against expansion, urged BAA to abide by the decision.
Terry Morgan, Stansted's managing director, said the airport would appeal and seek to have the issue decided by a government inspector at a planning inquiry.
He said the airport would push ahead with plans to build a second runway, which they expect to be opened in 2015.