This article presents a new analysis approach to design and evaluate motor vehicle inspection and maintenance (I/M) programs. The new approach, called I/M-Design, uses real-world data to provide two resources not previously available: (1) a transparent framework to quantitatively illustrate the range of emission reductions available from I/M, and (2) a sensitivity analysis tool to evaluate how key variables affect I/M performance. In addition, the approach satisfies a policy-making information need--how to convey, in a logical and straightforward manner, the expected benefits from I/M without relying on modeling tools inaccessible to those outside the air quality field. The material presented in this article illustrates the new approach by estimating hydrocarbon (HC) emission reduction benefits available from enhanced I/M in southern California's South Coast Air Basin. I/M-Design estimates that enhanced I/M results in a 14-28% reduction in light-duty motor vehicle HC exhaust emissions; this estimate compares well to other California I/M program evaluations. Even more importantly, I/M-Design sensitivity analyses illustrate how I/M programs that implement stringent failure thresholds, motivate pre-test repair work, and improve repair effectiveness can provide emission reductions that substantially exceed the performance of existing programs.