I understand Highways England are assessing this junction with a potential start date of March 2020.
Can't disagree with other comments. The Westbound A31 through the New Forest runs reasonably well until you hit Ringwood. Then in a very short distance, there's a slip road from Ringwood (which queues back into the town), a most peculiar little slip road by the Fish Inn, immediately followed by a petrol garage. As if that wasn't enough, the turn off to Verwood is straight after, followed by the road becoming 4 lanes and splitting between the A338 and A31. I can't imagine it was actually designed this way - it appears to have just "evolved".
There are daily queues, especially in the evenings and weekends. During holidays and peak times for tourists, the queues can be well back into the Forest - at least 15 minutes and up to an hour. If there's any kind of accident the queues can occasionally stretch all the way back to the M27.
There is a frustratingly selfish yet popular "rat run" at the Hightown/Poulner junction just before Ringwood. Cars leave the A31, go up the slip ramp, across the tiny roundabout and back down the other side to re-join the A31. It's sometimes like a procession of vehicles. When traffic on the A31 is near stationary , it saves perhaps a minute however just adds to the overall problem.
The whole are is a pinch point and most frustrating for many drivers.