State vehicle emission testing programs have had little impact on getting the
worst polluting vehicles off the road, according to a report by the National
Research Council of the National Academies.
The report says states and the Environmental Protection Agency (EPA) have
overestimated the amount of smog reduction achieved by inspection programs.
Older and malfunctioning vehicles make up about 10% of the total number of
vehicles but emit about 50% of the most harmful air pollutants
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