So, without RTFA, the summary is misleading. It makes it appear like this program is a novel thing that has never been done.
In reality, Mexico City has been keeping a percentage of vehicles off the road for pollution fighting purposes since 1989. Vehicles stay off the road one working day per week according to their license plate's last digit.
Newer (10 years old or newer) cars were allowed to drive every day. Also, while all cars have to pass mandatory emmissions control, that had no effect on whether they could be on the road (so for instance, a newer but more polluting car would be able to go out every day while an older, potentially less-polluting car would have to stay home one day a week).
Earlier this year a court mandated that the permit to be on the road daily should be tied to the car passing emmissions control. More cars on the road are part of the reason why pollution levels reached a high-enough level to prompt the government to remove all exceptions to the program and have all cars, irrespective of age and pollutant output, stay home one day a week.
Incidentally, this program is part of the reason why there are so many cars in Mexico City: faced with the prospect of not being able to use the car once a week,many families bought a second car to also have coverage on the first car's off-the-road day.