Findings from a study that attempts to monetize the costs of transport air pollution in Santiago, Chile, are presented. The costs per pollutant used in the study come from a 1994 World Bank study estimating morbidity and mortality costs of air pollution in Santiago, based on productivity losses and treatment costs. Using MOBILE-derived vehicle emissions factors and estimated vehicle distances traveled by various vehicle types, the total estimated transport pollution costs incurred in 1994 are presented. Also presented are estimated average air pollution costs per passenger kilometer traveled for pre- and post-EPA87 standard autos and taxis and pre–and post–EPA91 standard buses, as well as for Santiago’s Metro (urban heavy rail). Future air pollution trends in Santiago are discussed, and a theoretical discussion of the potential application of these cost estimates for transportation policy making in the city is provided.