Study calls for rethink on vehicle emissions tests

Testing inefficiencies, maintenance inadequacies and other factors have led to 4.6 million tons more harmful nitrogen oxides (NOx) than standards allow, according to the study that has been published in Nature.

The findings are said to reveal major inconsistencies between what vehicles emit during testing and what they emit in the real world, a problem more severe that the Volkswagen incident of 2015 when it was found that millions of new diesel cars were fitted with so-called defeat devices.

The devices sense when a vehicle is undergoing testing and reduce emissions to comply with government standards. Excess emissions from defeat devices have been linked to about 50 to 100 US deaths per year, studies show.

"A lot of attention has been paid to defeat devices, but our work emphasizes the existence of a much larger problem," said Daven Henze, an associate professor of mechanical engineering at CU Boulder who, along with postdoctoral researcher Forrest Lacey, contributed to the study. "It shows that in addition to tightening emissions standards, we need to be attaining the standards that already exist in real-world driving conditions."