I think it is hard to find a balance between enforcement, realism and stringency. If you make enforcement hard and standards stringent, with no realism, you wi

I think it is hard to find a balance between enforcement, realism and stringency. If you make enforcement hard and standards stringent, with no realism, you will get cars that are optimized to pass a test that doesn't help in practice. If you make enforcement hard and tests that are realistic but too easy, you will get an improvement, but maybe not as good as it may be. And if you loosen up on enforcement and make test that are both realistic and stringent, manufacturers will cheat. If you make all three hard, you just shift the problem, manufacturers will either optimize for tests, do not enough, or cheat depending on what is the balance between the three.