The gap is presumably due, to a great extent, to the lack of accurate deregistration of vehicles that are scrapped or no longer in use, which is reflected in the fact that these vehicles are not enrolled in the inspection and maintenance programme. Nonetheless, the role of the CAMe (like that of other metropolitan commissions) has been limited by the lack of a legal framework with binding mechanisms for ensuring co-operation from state- and municipal-level governments. The metropolitan commission framework is explained in detail in Chapter 5. In the case of the vehicle restriction scheme, Hoy No Circula, considerable controversy about its effects on air quality improvements has arisen.