California wants to get smog-machines off the roads, and to that end it is planning an experiment that would help detect the black sheep among the millions of vehicles on the freeways of the state. "In the largest experiment of its kind in California, the South Coast Air Quality Management District plans to use remote sensors and video cameras to measure air pollution from 1 million vehicles as they enter freeways and navigate roads in the counties of Los Angeles, Orange, San Bernardino and Riverside. If caught, the owners of the most environmentally offensive cars and trucks would receive letters informing them that the government would pay to fix or scrap their vehicles. The South Coast district estimates that 10,000 to 20,000 of the dirtiest vehicles would be detected. Smog regulators lack the authority to order drivers to dump dirty cars, but they can offer incentives." It is estimated that one tenth of cars produce half of the emissions responsible for smog, so such an initiative could have a significant impact on air-pollution. If it works well, we hope that all big cities will do it too.