Paris officials are seeking drastic measures to combat an alarming spike in air pollution that has turned the city's skies a murky gray.

Mayor Anne Hidalgo called on the government to implement an emergency ban Friday on around half of the car and truck traffic. Thursday was the third straight day that air pollution has registered far above European safety thresholds.

The measure was last taken a year ago during a previous peak in pollution. Hidalgo also called on regional transport authorities to make subways, trains and buses free for the day. The city's car- and bike-sharing programs will also offer incentives to cut motor vehicle traffic in the city Friday.