A fundamental decision to be made in developing a motor vehicle Inspection and Maintenance (I&M) program is whether a “centralized” or “private garage” program will be used. Under the centralized approach, the state or a state contractor operates a network of single purpose “Inspection Centers” to inspect motor vehicles before the completion of the annual registration renewal process. After any repairs necessary to correct vehicles with excessive emissions are made at a facility of the owner's choosing, the vehicle must pass a reinspection at the Inspection Center. Under the private garage (decentralized) approach, both inspections and repairs are conducted by private repair facilities licensed by the state.A comparison of a centralized I&M program and a private garage I&M program currently operating in California indicates that the centralized program is providing over ten times greater emissions reductions. The superior performance of the centralized program appears to be due in large part to the fact that emissions related defects are more efficiently and reliably identified with the use of highly automated Inspection Centers. The fact that vehicles with excessive emissions are independently reinspected to check the quality of the repairs performed also appears to be a factor contributing to the superior performance of centralized I&M programs.An analysis of the potential for upgrading both programs indicates that the private garage approach is unlikely to ever be competitive with a centralized I&M program.