Is there a standard? What standards body has decided it and where can I see it's tests enumerated?

Or do you mean the quick and dirty 'field sobriety tests' that many police offers use? I'm not aware of those being actual standards or tests so much as quick and dirty tools to justify the effort of /actual/ standards tests (BTW, I recall hearing that you should always demand the blood test over the breath tests).

I think blood alcohol content counts as an objective standard.

Yes, many states in the US (and I presume other governments at some level around the world) have BAC level tests that are a legal limit which has a strong scientific correlation to of resulting in impaired driving and decision making.

I think there might be some debate over variance of correlation among different ethnicity and experience level of particular users, but I cannot recall any actual disagreement about the current legal BAC limits being close enough for the general population.

However that is the point being made by the parent article; that while presence of alcohol in someone's blood does have that strong scientific correlation there is as yet no strong scientific correlation for any of the legal limits currently in place.

BAC is only a legal standard, not a physiological standard.