What is Clean Air Zone?

A Clean Air Zone (CAZ) is an area where targeted action is taken to improve air quality, often by charging the most polluting vehicles to enter. Cities including Birmingham, Bristol, Bath, Sheffield, Bradford and Portsmouth operate CAZs under a national framework, with classes A to D determining which vehicle types are charged. CAZs differ from London's ULEZ in operator and pricing but share the same goal of reducing nitrogen dioxide from older diesels and petrol vehicles.