It might be the most obviously unfinished motorway in the whole UK, let alone in London. The M23 was supposed to link London with Crawley - but its urban section was a problem that couldn't be solved.
It was the UK's only single-carriageway motorway, and twenty years ago it ceased to exist. This is the story of the strange fascination it held, and of my place in history.
A field guide to the UK's road signs, explaining the colours, shapes, symbols and everything else you need to know to avoid putting a foot (or a wheel) wrong.