> Nobody thinks it's ok to drive with a BAC of 0.4 but 0.04 is generally considered legal.

Unfortunately, even 0.04 can get you arrested in California.

The BAC limit is simply when the DMV automatically pulls your license. You can be convicted of DWI/DUI at any BAC in California.

Now, you aren't likely to get pulled over at BAC less than 0.05, but if you do get pulled over, you can still get convicted for it.

BAC exists because a test exists to easily measure it. Breathalyzers aren't perfect, but they're good enough for government work.

I think an actual blood test is the only thing we got for MJ. That's invasive, and not likely something officers will be able to do at a traffic stop.

> Nobody thinks it's ok to drive with a BAC of 0.4 but 0.04 is generally considered legal.

Not sure how you come to that conclusion. I think it's reasonable to assume it's legal because most people (including me) feel it's fine. I'm much more concerned about distracted driving generally.

A BAC of 0.04 is measurably impaired though. Mostly in terms of higher brain functions and reaction times making it both less obvious and often within a persons 'normal' range.

Something to remember is people generally drink late in the day. So, the accident statistics mix drinking and tired data. Tired driving makes things far worse, but it's hard to test for as accidents and being pulled over both tend to wake people up. Pot on the other hand is more often a daytime drug which is going to mess with the statistics.