The M876 is a little motorway that makes a shortcut between the M80 and M9, and provides a way for traffic between Fife and Glasgow to go from the M80 to the Kincardine Bridge. It borrows a mile of the M9 to do it. For many years, most of the M876's traffic was put straight onto the single-carriageway A876 at the eastern end, but the construction of the Upper Forth Crossing included improving the A876 to a dual carriageway and grade-separating junction 3, so its terminus is now rather more dignified.
Before the motorway was built, the short spur from junction 2 and the route west of there was a dual carriageway section of A-road. When motorway restrictions were applied, nobody seems to have checked the road to see if it had any features that weren't suitable on a motorway. There's still a pedestrian crossing part way along the spur, complete with paved section over the central reserve! This appears to be the only such crossing on any British motorway.
The M876 is the only motorway in Britain for which the basic rules of maths were re-written. Follow the junction numbers in order and you'll find yourself counting 5, 1, 2, 8, 7, 3!