Where is it?
M5 junction 11A. The connection between the M5 and M4, taking in Swindon and Cirencester on the way, arrives at the M5.
What's wrong with it?
It's a bit of a tangle really. Some areas have full free-flowing links, some have a roundabout, some have no links at all. The roundabout over the A417 is seemingly unnecessary (one side isn't even used) and the wide sweeping curves, while very nice and graceful, take up a rather astonishing amount of land. The piece de resistance is that (from personal experience at least) the junction tends to have nothing but a couple of cars tootling around the expanse of tarmac.
Why is it wrong?
One assumes that some links are more important than others. Since the A417 forms part of a link to and from the M5 from points south, links to the M5 north are prioritised here. The roundabout can also (perhaps) be explained by what appears to be a new dual carriageway in the aerial photo, under construction there, maybe now finished. Whatever this road serves now has a connection to the junction, though curiously not the A417 westbound.
...Several years on, that dual carriageway is now open and the roundabout makes sense. You could still do with a westbound entrance slip, though.
What would be better?
Providing the missing westbound on-slip to the A417 would be a nice start, so at least no movements from the new road have to take in surface streets.
Right to reply
I went through this junction a couple of weeks ago. The reason for the "missing" slip road off the roundabout onto the A417 is because the motorway slip road has already started and there's not enough room to fit it in (without weaving). What does seem to be the biggest problem, which hasn't been touched upon, is there's no northbound motorway access at all to the roundabout junction (and thus the spur to Gloucester Business Park), which seems very strange. Do they only want traffic from Bristol?
Clearly your motorway designer has never tried to drive around the Gloucester ring road from the south in the rush hour. Access Northbound from the West would reduce the traffic flow on the ring road (which is, incidentally, one of the poorest excuses for a bypass of any city in the country. If he's responsible for that too, I'd like to strangle him).
The dual carriageway under construction in the photo [since updated] connects the junction to the Gloucester Business Park. The decision not build a direct northbound access to the M5 here was - as things tend to be in the UK - very shortsighted, as the Business Park is one of the biggest development sites in the south west with many major distribution warehouses established as well as thousands of houses on the way.
The other day (admittedly due to bad weather conditions) the A417 was at a standstill, so having come off the M5 northbound at 11A and trying to get to Cheltenham I thought the best option would be to get back on the motorway and try the next junction up - junction 11. It turns out that this is impossible as there is no way onto M5 northbound and no slip road onto A417 westbound. Why can you not do either? Am I missing something here?
So if there's a westbound on-slip from the roundabout then there needs to be a link from the M5-A417 southbound as this slip road doesn't connect to the roundabout. To me it should've been a 3 level stack roundabout interchange so all movements are possible with possible on off slips from the M5 southbound to the A417 eastbound.