Develop a roadside impairment test (not a test for substances in your body; a test for the actual ability to respond to the environment at a level that lets you drive with reasonable safety).

If you get pulled over and can't pass the test, you lose your driver's license, regardless of the reason you're impaired. If you can demonstrate that you would have had no reason to suspect the possibility that you might be impaired, you can get the license back; otherwise it's gone for a determinate and long period of time.

If, on the other hand, you can be shown to have had specific KNOWLEDGE that you truly WERE impaired, that's a criminal offence. If you can't pass the test and you have no driver's license, that's also a criminal offence, regardless of your knowledge.

Replace all substance-based driving laws with that.