Decades ago Mexico City’s air pollution was so poor, birds would fall out of the sky—dead. Locals said living there was like smoking two packs of cigarettes a day, according to one report. In response, Mexico City took several steps to try to improve air quality including restricting driving one or two days during the weekdays. The program has had negligible results.
In 2008, the city added driving restrictions on Saturdays in hopes of moving the needle but according to new research by Lucas W. Davis, an associate professor at UC Berkeley’s Haas School of Business, extending the program one more day also isn’t working.