A series of roadworks to demolish two bridges over the M27 will begin this week - and will see the motorway closed in both directions.
Closures will be in place between Junction 3 and Junction 5 from Friday (September 28) night to Monday (October 1) morning.
And motorists are facing a 60 mile diversion if they are heading westbound on the motorway this weekend.
Here are the full routes of the diversions in both directions:
Traffic on the eastbound M27 will be diverted off the motorway and directed towards Romsey.
High-sided vehicles will be diverted along the A27 through North Baddersley to re-join the M27 at junction 5, avoiding the low bridges in Romsey.
Vehicles not exceeding the height limit will be diverted along the A3090 to the M3 just south of Winchester.
The westbound M27 will be diverted via the M3, A34, A303, A345, A36 to re-join at junction 2.
The westbound diversion will also be signed from junction 8 on the M3 so that southbound M3 traffic can join the diversion route by using the A303.
There will also be a diversion route for the A3057 (Romsey Road) itself.
This work has been carefully planned and agreed with Hampshire County Council, Southampton City Council, Hampshire Police and other stakeholders.
While the motorway is shut, Highways England and its contractors will use the closure to carry out routine maintenance, such as vegetation clearance and drainage work.
When the A3057 reopens on Monday morning, there will be a single lane over the bridge, which will be traffic light controlled.