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Driving Restrictions Haven’t Cleared Mexico City’s Air

Residents go out of their way to avoid public transportation, a new study argues.

By Nathan Collins


A general view of the smog covering the Mexico City skyline on March 30th, 2014. (Photo: Yuri Cortez/AFP/Getty Images)

Mexico City is not known for having clean air. Over the past 25-plus years, the city has taken some efforts to cut air pollution, namely through tight restrictions limiting the days people can drive their cars. But, according to a new study, recent expansions of those plans haven’t worked out—air pollution, it seems, is just as bad as before.

Mexico City’s program, known as Hoy No Circula (or No Circulation Today), isn’t complicated: Since 1989, drivers have only been allowed to use their cars four out of five weekdays. The city uses license plates to determine who gets to drive when. For example, cars with plates ending in a five or six have to stay home on Mondays. In 2008, the program expanded to include Saturdays as well, in the hope that doing so would further tackle the pollution problem.

Unfortunately, that strategy hasn’t worked, University of California–Berkeley economist Lucas Davis writes today in Scientific Reports.

To reach that conclusion, Davis compiled air quality data from the Automated Environmental Monitoring Network, which monitors carbon monoxide, nitric oxide, particulate matter, and other pollutants at 29 stations around Mexico City. An analysis of trends in that data before and after the 2008 expansion showed that it had no effect on air pollution, with the possible exception of average, but not peak, carbon monoxide levels. Those, Davis found, may have leveled off after 2008.

The problem, however, is that people don’t abide by the law, Davis found. At least, not as it’s technically written.

Mexico City residents did a number of things to get around the ban, like taking more taxis and buying another vehicle to, in effect, have a legally drivable car every day of the week. And while people take rapid transit buses now more than before, that could reflect a pre-existing trend, according to Davis. Meanwhile, Mexico City residents are using about as much gasoline as before, and there does appear to have been a jump in new car registrations around the time of the Saturday expansion.

In other words, Davis writes, people didn’t stop using cars—they just got some other car to get around in. “Moving forward, this is not going to get any easier with the increased global availability of taxi-like services like Uber. As incomes continue to increase around the world so does the value of time and thus the preference for private transportation,” Davis writes.