Most auto emissions come from the dirtiest ten percent of the cars on the road. Why should we ignore this fact? Daniel Klein suggests using infra-red beams to measure the quality of auto exhaust from particular cars, as they drive by the sensors. Identify the minority of gross polluters by photographing their license plates, and then get them off the road, force them to fix their cars, or tax them. Note that your annual or bi-annual auto emissions test is easy to fake or prepare for. Under Klein’s scheme the government measures the quality of auto exhaust, and lets the car owner invest in a better result however he or she wishes to do. My main worry concerns privacy issues, but perhaps privacy is headed out the window in any case. To read about related essays on economic policy and technology, from the same book, see my previous post on electricity.