THE PURPOSE of this paper is to evaluate the concept of using remote emission sensing under controlled conditions to quickly identify clean vehicles (operating on gasoline, natural gas, or propane) and eliminate them from further testing in a mandatory vehicle emissions inspection and maintenance (I/M) program. The test procedure involves performing remote sensing measurements of light duty vehicle exhaust emissions as the vehicle is driven under controlled conditions in a prescribed manner past three remote sensing units. All vehicles in this project were then subjected to IM240 chassis dynamometer testing to determine the accuracy of the prescreen result. Third party quality control/quality assurance/auditing was employed to ensure data integrity and reliability.Data is presented illustrating the tradeoff of IM240 program effectiveness versus prescreen pass rate for the non-preconditioned and the preconditioned fleet applying US EPA Final IM240 Standards. The Ontario IM240 Proposed Phase-In standards case is also examined where the remote sensing prescreen may be used as a valuable tool in easing the introduction of, and improving the public convenience of a potential mandatory I/M program in southern Ontario.