Smog-alert car ban jams metro, buses in Mexico City

Pollution levels were down somewhat Wednesday, but Martin Gutierrez, executive coordinator for the Environmental Commission of the Megalopolis, told Milenio TV that the alert would remain in place until at least 5 p.m. A dense haze obscured the volcanic mountains that ring the city.

On any given day a fifth of all cars are supposed to stay off the streets, but that doubles during a Phase 1 alert.

[...] recently, newer and cleaner cars were exempt.