The European Union (EU) is adopting a tougher emissions tests for new models of cars.
It said that this would better reflect ordinary driving conditions, as many cars on the road emit up to four times more pollutants than the technical limit.
The new rule is expected to start from 2017, but critics say the tests are not strict enough, as car makers would still be allowed to exceed emission limits.
The move comes as car giants Volkswagen faces a scandal over falsifying tests.
Diesel vehicles are a major source of nitrogen dioxide, which has been linked to respiratory diseases and premature death.