tiagosilva29, on 16 September 2012 - 11:18, said:
It is illegal/finable/detainable if you're publicly intoxicated in some states, therefore the concept of a designated driver is useless in those states. Even if you are on a private vehicle, you had to access it via public space, and note that if you are driving this person, you are driving this person on a public road.
I think it varies from state to state just as it varies from province to province in Canada. In the province that I live in (Ontario), you won't be issued a ticket or arrested unless: A) You pose a threat to the people around you. B) You disturb the public by screaming, singing loudly, swearing, etc. C) You lose consciousness in a public place.
Also, it's highly unlikely to be stopped between a designated driver's car or taxicab and a bar/restaurant. I know because I've had a couple of police officers joke around with me about how boring it is to be a designated driver. The same officers also wished my friends a fun night (within the limits of the law, of course). I've also seen police officers walk by people at night that are clearly intoxicated in Toronto's entertainment district (but not intoxicated enough to scream or pose a threat to those around them).
So yes, you're right about it being illegal to be publicly intoxicated. However, I believe it varies from place to place (even within a city). For example, I wouldn't be surprised if someone was arrested for public intoxication in a quiet uptown neighbourhood as opposed to a downtown entertainment district. In places like that, it's unexpected for people to be publicly intoxicated. And in places like Toronto's entertainment district, it's expected for people to be publicly intoxicated during the night.
In my opinion, the law usually applies to people that haven't made any arrangements or plans to get home safely.