One of the simplest ways of cutting down on transportation pollution is to keep your car well tuned. Inspired by the U.S. Clean Air Act of 1972, many cities and states have now implemented annual or biannual emissions testing to determine if cars are producing excessive amounts of pollution at the tailpipe. Car owners whose vehicles flunk the test are legally required to bring their emissions maintenance up to spec. This has already been surprisingly effective at reducing pollution. For years the city of Los Angeles, which is ringed by freeways packed full of cars, was famous for the yellow haze of smog that hung in the air and stung the eyes and lungs of visitors and residents. Today, partly because of the vehicle emissions testing program instituted by the California Air Resources Board (CARB) in 1982, Los Angeles smog is largely a thing of the past and the sky above the city is blue again.