ROBERT SIEGEL, HOST:
This is ALL THINGS CONSIDERED from NPR News. I'm Robert Siegel.
AUDIE CORNISH, HOST:
And I'm Audie Cornish.
And if you're trapped in traffic right now, or even if you're not, don't take your eyes off the road. Just let your mind drift slightly and think of Paris. That's where a spike in air pollution has driven the government to ban half of all cars from the road. Several cities in France are giving it a try, and Paris has the most severe restrictions.