M27 Widening
The schemes had been planned since the early millennium, and to be fair they were needed. Junctions 3 and 4 aren't very far apart, and between them lies Rownhams services. Junction 3 is for the M271, which is the main route in and out of Southampton and its docks, and junction 4 is where the M3 branches off taking a lot of traffic for London, Winchester and The Midlands. As a result, you get a lot of traffic 'junction hopping'.
The other problem here is that this is the main road to Southampton, but it wasn't meant to be. The original plan was that traffic heading south on the M3 would be directed on to the M27 west towards junction 5, where a new motorway would take traffic in to the city, with the M271 being used only by traffic coming from the west. Obviously, that didn't happen, and this together with a general rise in traffic levels has led to regular congestion.
J11-12 is no better, because here the road climbs steeply to mount the bottom of Portsdown Hill (it climbs about 230ft over 1 mile), and then descends towards Portsmouth in a section of road known locally as Apache Pass. The problem is that on a motorway there are lots of cars which don't mind staying in the inside lane with all the lorries, but as they approach the hill the lorries slow down to climb it, so the cars pull out in to the middle lane. However, these cars don't like travelling fast (that's why they stay with the lorries), so everyone who is usually in the middle lane pulls out in to the outside lane, and everyone who is usually in the outside lane has to... oh dear. That's how the queues build up, and although there is a good excuse for J3-4 being busy there isn't one here, as the motorway is only 30 years old and the hill has always been there. The M3 came along 10 years later and, on a much gentler slope it got a climbing lane. Strange.
Here are a large selection of photos taken during the roadworks, focusing largely on the climbing lanes because they're closer to me.
Further Reading
Highways Agency - official website for the widening works and climbing lanes.Roads.org.uk - Futures - M27 Widening- SABRE discussion thread