In the United States, automakers conduct their own emissions tests and submit the results to the government. In Europe, automakers pick who conducts the tests and where they are done. And these two regulatory systems are considered the world’s gold standards.

Questions about the wisdom of allowing automakers so much sway in how air pollution standards are enforced grew this week after the resignation of Volkswagen’s chief executive, following the company’s diesel emissions cheating scandal.

Regulators in several European countries have opened investigations, attorneys general in the United States have joined federal inquiries, and there has been broader criticism of Volkswagen, and diesels, in markets from South Korea to Brazil.

Volkswagen has admitted installing software in 11 million vehicles that was used to provide false results about emissions, though it was not clear if it was used in all countries where the cars were sold. But the breadth of the scandal could finally threaten to bring change to an industry with a record of cheating since cars were first regulated.