In a letter to car manufacturers, the EPA said it will add on-road testing to its regimen, "using driving cycles and conditions that may reasonably be expected to be encountered in normal operation and use, for the purposes of investigating a potential defeat device" similar to the one used by Volkswagen.
The testing would be in addition to the standard emissions test cycles already in place, the EPA said.
The revelations about VW led to unwanted scrutiny for the EPA. Its testing procedures have been criticized for being predictable and outdated, making it relatively easy for VW to cheat using what governmental officials repeatedly describe as a "sophisticated scheme" determined to game the system.
EPA did not initially uncover the problem; researchers at West Virginia University did, using on-road testing that EPA did not.
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"It's not a question of equipment or technology or capability. It's a question of where we deploy those resources," Grundler told reporters.
The EPA has conducted on-road testing on heavy duty trucks, rather than passenger cars, "because that's where the emissions are," he said.
VW has admitted to installing so-called defeat devices on Volkswagen and Audi cars with four-cylinder diesel engines.