Thanks Dean, it was for this new page on my website http://groups.msn.com/davidskingsburycollection/di dyouknow.msnw
They
still didn't really know why they started at 100, but I think there weren't enough B roads good enough to qualify, or they'd have been A roads. I also noticed A roads aren't always numbered lower for longer as the A 200 at Tower Bridge barely goes anywhere.