In the Medford area, all 1980 model year vehicles and newer must be tested. Cars, truck, vans, motor homes, and buses powered by gasoline or alternative fuels, such as propane or diesel, with manufacturer's gross weight rating of 8,500 pounds or less must be tested. DMV notifies vehicle owners when the vehicle registration is about to expire. For most vehicles, this is every two years. The notice includes information about the required vehicle inspection .
Vehicle inspection is designed to help reduce smog and carbon monoxide levels.
The Portland-Metro and Rogue Valley areas used to have significant levels of smog and carbon monoxide, but pollution levels have been dramatically reduced since the implementation of the program. Currently, over 30 states have vehicle inspection programs. The black smoke emitted from diesel trucks and buses is fine particulate matter or soot. While this is a serious pollutant, the Environmental Protection Agency has not yet approved a standardized inspection process for heavy-duty diesel engines. Diesel vehicles are minor contributors to a region's smog problem.