This is the logic that European politicians have used in the past.

If there were a direct relationship between lab test emissions and real-world emissions, that approach may be acceptable. Unfortunately, that is not the case.

In the case of NOx, implementing the Euro standards should have resulted in an 80% reduction in emissions over the past 15 years. As the vehicle fleet is renewed, that should have translated into significant reductions in kerbside NOx levels. But this has not happened, and London continues to suffer some of the worst NOx levels in the world.

It turns out that an 80% reduction in lab test emissions has not translated into anything like an 80% reduction in real-world emissions - not even close!

The current system is inadequate because manufacturers simply "design for the test". There is huge real-world variability between vehicles that may record very similar lab test scores. A vehicle may claim similar test score results as another, but in fact have hugely differing levels of emissions in the real world.

Test environments need to reflect real-world conditions!