An analytical tool is developed that is capable of predicting both present and future transportation policy impact on urban air quality. The Transportation Air Pollution Analysis Procedure (TAPIP) combines a versatile traffic assignment computer program model with an urban diffusion computer program model. TAPAP assesses the air quality impact of transportation policies such as extra lanes to an urban freeway, construction adding of new roadways, changes in auto emission standards, and exclusive bus lanes. With the stringent air quality standards now being legislated, TAPAP's ability to quantitatively measure a transportation system's present and future impact on air quality is indispensable to urban planning. The TAPAP program utilizes a modified version (APRAC-EM) of the original APRAC-1A urban diffusion computer program model. APBAC-EM, with its emission model, more effectively stimulates CO concentrations during peak-hour periods when CO concentration are most critical. / Master of Science