The proposal of transportation control plans formulated to bring the air quality of U.S. major urban areas into compliance with the mandates of the Clean Air Act has created considerable public concern about the social and economic implications of these controls. The purpose of this paper is to analyze the impact and feasibility of key components of the plans being proposed and to examine the relationship between the implementation of a set of feasible transportation controls and the attainment of the air quality standards. Important inspection/maintenance and hardware retrofit approaches to motor vehicle emissions control are described and estimates of their effectiveness and costs are presented. Measures designed to control emissions through reducing auto use are discussed.