Mexico City declares 3rd day of traffic cuts over high smog

Mexico City is ordering 40 percent of cars and trucks to stay off the streets Thursday, extending for a third day a traffic cutback aimed at lessening pollution.

Under a rule in effect through June, one-fifth of the city's vehicles normally must stay at home on a weekday, with the day determined by license plate numbers.

But on Wednesday, smog stayed above 1½ times acceptable limits for a third straight day, meaning an additional 20 percent of vehicles can't be used Thursday.

Ozone, a key component of smog, reached almost 1.8 times acceptable limits.

Before the rule was implemented last month, newer or cleaner cars were exempt from the one-day driving ban.

The pollution spike is due to seasonal weather patterns and the increasing number of cars in the city.