In 1989, the government of Mexico City introduced a program, Hoy No Circula, which bans most drivers from using their vehicles one workday per week based on the last digit of the ve- hicle’s license plate. The program has been strictly enforced and has been since emulated in Bogota, Santiago and S˜ao Paolo. This paper measures the effect of the driving restrictions on air quality using high-frequency measures from monitoring stations. Across pollutants and spec- ifications there is no evidence that the program has improved air quality. The policy has caused a relative increase in air pollution during weekends and weekday hours when the restrictions are not.
