Bicyclists have taken free rein of Milan's streets during a six-hour ban on private cars in a bid to alleviate persistent smog.

Pollution levels in Italy's business capital have exceeded levels considered healthy for more than 30 straight days, prompting officials to ban private cars from 10 a.m. until 4 p.m. Monday through Wednesday this week. Rome, which is also battling smog, has been enforcing alternate day driving based on odd and even license plates, while Florence has announced limits on automobile access to the historic center through New Year's Eve.

The lack of rain and winds has exacerbated pollution levels in Italy, particularly in the mostly land-locked northern Po River Valley.

Health officials say vehicle emissions account for half of the pollution in Milan and 70 percent in Rome.