Low Emissions Zone (ULEZ) is well-publicised but other cities' Clean Air Zone (CAZ) rules are inconsistent and confusing for motorists. Our guide clears the fog. What is a CAZ? We explain all Find out ...

The largest Clean Air Zone is the ULEZ (Ultra Low Emission Zone) in London. Clean Air Signs typically have a dark blue background and feature a cloud, which is surrounded by a green circle.

The Ultra Low Emission Zone (ULEZ ... morning in London and most people probably won't notice anything has changed. But London has taken a big step in trying to clean up its air.