Driving restrictions that work? Quito's Pico y Placa Program

Programs to reduce traffic congestion and air pollution by restricting use of motor vehicles on working days have generally not met with success, given existing studies of such programs. We conduct the first study of Quito, Ecuador's four-year-old Pico y Placa program and find that it has reduced ambient concentrations of carbon monoxide (CO), a pollutant primarily emitted by vehicles, by 9% to 11% during peak traffic hours. Given that ambient concentrations of CO generally track the spatial and temporal distributions of traffic, these reductions in pollution suggest similar reductions in vehicle flows. We find no significant evidence that traffic has shifted to other times of the day or week, or to other locations.