Shortly after passage of the 1990 Clean Air Act Amendments, the US Environmental Protection Agency issued regulations governing motor vehicle inspection and maintenance programs. These rules mandated test-only inspections and narrowly-defined test procedures; they proved politically unpopular and were eventually overturned. Acquiescing to state concerns, the federal government granted flexibility to experiment with various program options. An interest among states was whether remote sensing might identify high-emitting vehicles inexpensively and unobtrusively. Several states implemented remote sensing device policies. In the intervening years, implementation experience has shown that remote sensing devices, though useful in ways unanticipated, fall short of expectations. Over time, federal mandates were revised to abandon traditional exhaust-based emissions tests in favor of computer-assisted inspections that take advantage of on-board diagnostic equipment. Experience has shown that computer-assisted inspections supplement, rather than replace, exhaust-based tests.
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