It has long been known that emissions from motor vehicles contribute significantly to the air pollution problems observed in many urban areas around the world. In response, governmental agencies, particularly in the United States and Canada, have adopted stringent emissions standards for new light- and medium-duty vehicles which require the use of emission control system capable of reducing emissions by 90% or more relative to uncontrolled vehicles. Because these emission control systems are subject to deterioration, malfunctions and tampering, all of which reduce system effectiveness, many areas have also adopted inspection and maintenance (I/M) programs for light- and medium-duty vehicles to identify and assure the proper repair of vehicles with high emission levels. In contrast, efforts to control emissions from heavy-duty vehicles (HDVs) has generally proceeded more slowly.
Sierra Research Inc., Lyons, James M.; Kear, Thomas; DiGenova, Frank; Macomber, S. Kingsley. 1994. Phase II Feasibility Study: Heavy-Duty Vehicle Emissions Inspection Program in the Lower Fraser Valley. BC Ministry of Environment