The legal system and propaganda machine need to shift focus. Criminalize the action, not the substance, and use any detected substance as evidence. As it stands now, if you blow a number, you are fucked. If you are fucked up on something that does not show up in a standard urine/blood screen, you cannot be convicted of a dui. (It is practically impossible, check the stats).
If we eliminate the DUI as a criminal offense, and prosecute all offenders who are reckless under the umbrella of reckless driving, we avoid that pitfall. We raise the maximum sentence for that offence, too. Now, you may say this change would not substantively alter the way the formerly charged as dui cases would be prosecuted, and that it is in fact cosmetic. But, i think a shit in the general attitude would occur as a result.
At the very least, it aids in shifting culpability away for the chemical and towards the individual. Jesus, our whole fucking society is bent on finding ways to avoid culpability, so we get a fucked up legal system...