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How do emissions tests work?

Controversies like the VW emissions scandal make you wonder exactly how do emissions tests work? Well, there’s a lot to it and the test differ depending on which side of the Atlantic you’re on. These tests are designed to keep cars within the letter of the Clean Air Act.
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Clean Air Act

The EPA, who are the United States Environmental Protection Agency, call for each US state to resolve multiple air pollution issues through programmes based on the latest science and technology information. For the automotive sector, the EPA’s regulations have far reaching consequences. They have to deal with hazardous waste disposal like other industries but they also have to adhere to specific regulations such as the rules governing engines. These regulations centre on emissions.

EPA emissions testing

The tests that govern a car’s emissions are carried out on production models in the US. The EPA put the car onto their dyno and run it through their computer controlled test rig to determine how much pollutant it puts out into the atmosphere. These tests are rigorous and accurate so drivers in America can be pretty much sure that the car they buy from the forecourt gives the quoted emission levels. Of course the VW scandal of 2015 suggests that this can be circumvented but VW went to lengths to disguise their car’s true emissions. Software that detected the car was being tested put it to the optimum configuration for the test. This configuration robbed the Volkswagen of performance and put extra stress on the engine which is why it was not run as the car’s default.

Testing in Europe

European testing is not as rigorous as it is in America. In Europe, car makers get to present a pre-production version of the car that’s specifically designed for the purpose. This suggests that the emission figures that company car tax and road tax are based on are not very accurate.

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