In this paper we investigate the effects of the temporal variation of pollution dispersion, traffic flows and vehicular emissions on pollution concentration and illustrate the need for temporally differentiated road pricing through an application to the case of the congestion charge in Stockholm, Sweden. By accounting explicitly for the role of pollution dispersion on optimal road pricing, we allow for a more comprehensive view of the economy-ecology interactions at stake, showing that price differentiation is an optimal response to the physical environment. Most congestion charges in place incorporate price bans to mitigate congestion. Our analysis indicates that, to ensure compliance with air quality standards, such price variations should also be a response to limited pollution dispersion.

Rationing car use based on license plate number has become a popular policy in several cities around the world to address traffic congestion and air pollution. This paper studies the effects of the moderate and drastic driving restrictions imposed as part of the Pico y Placa program on car use and air pollution in Bogotá. Using data on ambient carbon monoxide, gasoline consumption, and vehicle sales and registrations, no evidence of an improvement in air quality or a reduction in car use is found in either phase of the program. On the contrary, there is some indication that, relative to the moderate phase, gasoline consumption, vehicle ownership, and carbon monoxide in the morning peak tended to increase slightly when drastic restrictions were implemented.

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