Deciding what to do about the motor vehicle is characterized by conditions of complexity, value conflicts and uncertainty about the future. Doing something faces the difficulty of affecting a fragmented policy making process. Under such circumstances the most appropriate way to proceed is by seeking additional knowledge through research and experimentation. Research should start from the premise that motor vehicle restraints for clean air would probably entail measures much greater in scale and severity than currently contemplated. Measures of this magnitude imply practical and political problems of an entirely different order, and very probably, profound changes in city form and function as we know them today.