In the first year of the nonmandatory phase of New Jersey's idle inspection/maintenance program, over 3 million vehicles were tested in the state's 39 inspection stations. This paper investigates some equipment, procedural, and vehicle-oriented variables that can occur in an on-line system. The relationship of garage types of analyzers to the inspection network is also presented.The inspection equipment is described, and an assessment of its performance with design specifications is made. Operational procedures and manpower constraints are also described with relevancy to mass-production, quality-control applications.A recent proliferation of low-cost, garage-type, infrared exhaust equipment has made it necessary to evaluate and correlate such equipment to the inspection equipment. Special design features are presented, and a comparison of these features is discussed for those analyzers approved by the state of New Jersey.Finally, variables of the inspected vehicle population itself are investigated and compared with New Jersey's inspection standards.The authors conclude that, when taken collectively, inspection testing variables place an upper limit on the rejection rate that can be implemented in an idle inspection/maintenance control strategy.