The M271, a spur from the M27 towards Southampton's docks, is enormously useful but strangely designed.
It shifts traffic around the west of Southampton, connecting the motorway to the suburbs, docks and A33. It isn't a big job, and yet somehow the M271 manages to do it in the strangest way.
Its number is dubious, for a start. There are rules about how motorways should be numbered. The M271 lies entirely west of the M3, so really its number ought to begin with a 3, but it doesn't. That might make the more pedantic road enthusiast squirm, but it's not a big problem.
No, if we're looking for big problems, we need to attend to its interchange with the M27. Part way along the motorway, i's a roundabout with traffic signals, through which all M271 traffic must pass. That makes it - along with the A627(M) - one of the few places you'll find a set of traffic lights on the mainline of a motorway.
In fact, there's very little about the M271's design that would suggest that it is a motorway, if the roadsigns along its route didn't declare that it was one. There's only one junction on its route that doesn't require M271 traffic to stop. The one full junction worthy of a motorway connects only to a local road and an industrial estate.
But it could be worse. You can complain about the M271 not flying the flag for high standards of design and construction, or you can do without it and have heavy lorry traffic bound for the docks piling up through Southampton's suburbs. So, all things considered, it might not be so bad after all.