This paper investigates the impact of local traffic pollution on the formation of residential and business districts. While firms benefit from local production externalities, households commute to their workplaces with private vehicles and exert a local pollution externality on the residents living along the urban transport networks. The spatial location of firms and residents endogenously results from the trade-off between the production and pollution externalities and the commuting costs. The analysis shows that in monocentric cities the benefits associated with a fall in per-vehicle pollution are absorbed by rents paid to absentee landlords. When a city includes business and residential districts as well as a district mixing both agents,...