The M3 J9 upgrade project will see the number of lanes on the M3 increased from three to four through junction 9 as it passes under a wider gyratory, with free-flowing links between the M3 and the A34 in both directions.
It involves the construction of three new bridges, rearranging the main junction 9 roundabout and providing a number of other structures including new underpasses.
A joint venture of Balfour Beatty and VolkerFitzpatrick is main contractor for the project.
National Highways still has the price of the scheme at between £190m and £210m on its website but costs have spiralled sinc that was last updated. The Department for Transport is now allocating £290m for it.
Traffic can already be heavy in the area but is set to get worse, as 2,000 new homes are planned for Winchester.
Transport secretary Heidi Alexander said: “Anyone who uses this junction knows how frustrating it can be. But our £290m investment will save thousands of hours for commuters, tourists and freight every week, unlocking the true potential of our ports to deliver economic growth.
“We’re building rather than blocking so that we can get our economy growing. Approving these works, and the 2,000 homes it will support, is just another milestone on the way to delivering 1.5 million homes in this Parliament as part of our Plan for Change.”
