The radical £130m rebuild is needed to tackle heavy congestion which often causes traffic queues backing up onto the M3 northbound carriageway.
Around 110,000 vehicles use junction 9 every day, a large roundabout across two bridges, which goes above the M3. Congestion is expected to get worse with increased heavy goods vehicle traffic on the A34 and M3 from the proposed development of the Southampton container port.
The new WSP junction design will provide free-flow links between A34 and M3 with the A34 southbound link passing under the M3 with a 100kph design speed.
The A34 Northbound Link has a 120kph design speed. Junction 9 would be rebuilt with a dumb-bell roundabout layout and the whole scheme would require three new bridges.
The proposed free-flow interchange will help to reduce congestion by removing the need for through traffic to use the roundabout, in turn improving safety.
Subject to a successful outcome, construction could start in 2021 and take around two years to complete.
Highways England project manager Simon Hewett said: “Junction 9 is a vital interchange between the M3 and A34. With more than 6,000 vehicles using the junction each hour during peak times, it can often become congested, with queues backing up onto the main carriageway.
“The proposals we are publishing today will resolve that by separating out local and long distance traffic. With the new dedicated link roads, through traffic will not have to stop at the roundabout, freeing it up for local traffic and commuters.”