When air pollution blanketed Paris for three days, authorities called it the worst bout in 10 years and made public transit free. For the fourth time in 20 years, the city instituted a system based on alternating odd and even license plate numbers to keep certain vehicles off city streets, effectively cutting daily traffic in half; it’s the first time the ban’s been maintained for consecutive days. “Cars are poisoning the air,” says Paris city hall transport official Herve Levife. “We need to take preventive measures.”
Three other cities—Athens, Madrid and Mexico City—will ban diesel engines by 2025 as part of a similar effort. Beijing, China’s capital city, has such dirty skies from cars and coal that protective masks are commonplace despite emissions restrictions and power plant closures, partly due to pollutants from neighboring regions.
Paris leads the world in monthly car-free days, but several large metro cities participate in an international car-free day each September 22, including Washington, D.C., Seattle and Long Island, New York.