Eleven months of roadworks to widen a busy dual carriageway will begin in January.
National Highways is to widen the A31 on the Hampshire-Dorset border and replace the westbound bridges over the River Avon and Bickerley Millstream.
The scheme, costing between £25m and £30m, will create a third lane on the stretch at Ringwood.
A contraflow will be in place on the eastbound side from January to November while the westbound side is closed.
The slip road on to the westbound carriageway from Ringwood roundabout will be closed from November for preparatory work.
Alan Feist, National Highways' A31 programme leader, said: "Our plans will minimise impacts on road users while we demolish and replace the two westbound bridges and widen the road to three lanes.
"I can confirm that we will be able to maintain two lanes of traffic in each direction whilst we undertake the work from January to November 2022, keeping disruption to a minimum."
The roadworks will affect drivers travelling east from Bournemouth and those heading west from Southampton and the New Forest.
National Highways, formerly known as Highways England, is holding a series of virtual seminars and face-to-face information sessions about the scheme next week.