As part of its plan to improve air quality, the Government has required five UK cities to implement a clean air zone by 2020 in order to reduce levels of nitrogen dioxide.

Classes of CAZ

The Government framework sets out four classes of CAZ, distinguished by the types of vehicle covered.


Vehicles covered


Euro Standard




buses and coaches

taxis and private hire vehicles (PHVs)

M2(2) and M3

M1 and M2(1)

Euro VI

Euro 6

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