Scope and Objectives There is a need for an objective@ practical method of simulating the current and future impact of motor vehicles on air pollution in urban communities. Such a technique could be used to assess current concentration patterns of primary vehicular pollutants in cities@ and to predict the effects of exhaust emission controls and expressway routings on future concentration patterns. This report describes our progress in developing a simulation model designed to meet these objectives. Further refinements of this model are indicated and will be made in the course of our continuing study. In this sense@ the model is not yet a completely finished product@ and any present applications should be carried out with caution. In developing the model@ we have been aided considerably by previous urban diffusion modeling studies@ which have been reviewed and summarized by Wanta (1968)@ *Stern (1969)@ Moses (1969)@ and Neiburger (1968). An investigation of carbon monoxide diffusion in Washington@ D.C@ by Ott et al. (1967) and Clarke's (1964) model could be considered prototypes for the model described here. * References are listed at the end of the report.