Every now and again I have a burning question I need to ask about roads. Like why does the two lane A42 become the M42 at an apparently arbitrary point after which it continues with two lanes for many further miles? And I always turn to SABRE, the Society for All British and Irish Road Enthusiasts. I suspect the Irish must have arrived at the party after the acronym had been joyously pounced upon and the logo designed. If you are the sort of person who likes that sort of thing, it is a delight. They have a forum, in which they set each other quizzes, such as 'guess the road number' or 'identify fourteen badly drawn bridges' and get excited about rare street lamps.
It's a mine of information about roads, their history, their numbering (and its anomalies!) and an absolute must whether you like roads or simply enjoy immersion in other people's arcana.