Lower Thames Crossing between Kent and Essex to feature three lanes
A new road tunnel under the Thames Estuary will have an extra lane in both directions, highway bosses revealed.
The £6bn project will link the M25, near North Ockendon, Essex, with the A2 near Shorne, Kent, passing through greenbelt land.
Highways England said three lanes, instead of two, would make sure the Lower Thames Crossing and the Dartford Crossing could "work in tandem".
Other changes include a new junction at the port of Tilbury.
There will no longer be one with the A226 at Gravesend, Highways England said.
The project has been opposed by Thurrock and Gravesham Borough councils.
The changes were revealed at an event organised by the South East Local Enterprise Partnership (SELEP).
Tim Jones, project director for Highways England, said the alterations would give the capacity "for the whole network to work much better".
Under the plans, the new road will cross the A13 at Orsett and connect land east of Tilbury to land east of Gravesend.
Those behind the crossing say it will create 6,000 jobs and boost the economy by more than £8bn.
Mr Jones said addressing the visual impact would be an "important aspect" of the statutory consultation, which starts in summer 2018.
Christian Brodie, chairman of SELEP, said the new crossing would be good for local people and businesses.
"Anybody who lives in Essex or Kent and has tried to get across the river, will know how difficult and how uncertain it can be," he said.
"You never know if it's going to take five minutes to cross or whether it's going to take half an hour."
The planning application is scheduled to be submitted in 2019. Work on site is due to start in 2020, with the road open in 2027.