Earlier quoted context omitted.
Yes, in an ideal world we would do that. But by the time we come up with a perfect test that can be done roadside by police to determine driving impairment, that has very few false positives and holds up in court, we'll most likely have self driving cars and this won't be an issue anyway. I understand that everyone reacts differently to different drugs. Dale Earnhardt can probably be a little tipsy and still drive be…
Lots of behaviors impair your driving ability. A study found that being dehydrated caused the same number of driving errors as being drunk [0]. I'm sure it would be easy to make a field sobriety test for blood water content, but they don't, because safety isn't the real reason these laws get made. It's just public pressure to enforce moral values. [0]: https://www.telegraph.co.uk/news/health/news/11547199/Not-dr...
1. It only had 12 participants 2. One of those participants was excluded from the final results 3. They didn't test the participants' (or a separate group's) driving ability while under the influence of alcohol (they used a simulator, so it would have been fine), and so you really can't use the results to make any comparisons between dehydration and alcohol use 4. The study was funded by the European Hydration Institute
[0]: https://dspace.lboro.ac.uk/dspace-jspui/bitstream/2134/20400...