Call them zones, cones, segments or sectors, there are 9 of them in Great Britain. (and 9 different ones for motorways.) Here's a quick guide to them. The first digit of a road number should be the number of the zone it starts in, but more and more roads are breaking the rules...
Click "edit" above to add further examples to this list.
- A3400 map
- A38 A51 map photos
- A41 (at Birkenhead and London both East of A5)
- A5127 map photos