Did you know that a mini-M25 over the top of central London was once planned and started to be built? Here's the north section. As a fond user of the A102/A12 (née A102(M)) in East London, I'm sad to see that London missed out on actually having a decent traffic system.

While I'm on the subject of motorways, did you know there's a motorway with no number? Nor did I.