An infrared beam is projected horizontally across a single lane of traffic. As vehicles drive by, the beam passes through tailpipe exhaust, which absorbs some of the infrared light. A sensor and computer translate this into an emissions level. At the same time, an electronic license plate reader uses a video camera and computer to automatically record the vehicle's license number. Carbon monoxide, carbon dioxide and hydrocarbons.
Some units also measure nitrogen oxide emissions.
Millions of vehicles measured in several studies across the country have shown that remote sensing is a reliable method of detecting high polluters, with certain limitations. If a vehicle's engine is cold or if the vehicle is accelerating, emissions may be considerably higher than if the vehicle were cruising at a steady speed. Two faculty members at the University of Denver developed the technology in the late 1980s. At least two companies, including Remote Sensing Technologies of Denver and Santa Barbara Research Center, a subsidiary of Hughes Electronics. State officials are expected to use remote sensing as part of an enhanced vehicle inspection and maintenance program to detect and repair high polluters.