Conceivably, the same absolute standard could easily be applied to drinking in conjunction with driving. Furthermore, when it comes to protecting their own financial interests, bartenders often enforce standards beyond what it required by law: they may prohibit certain forms of attire associated with violent criminal gangs, and they often serve drinks in plastic cups, precisely because they are fully aware of the degree to which alcohol impairs good judgment and that glass bottles and glassware are capable of inflicting much more damage in situations where intoxicated patrons provoke physical altercations. In fact, bartenders know or should know that the social culture of alcohol consumption, particularly among certain demographic groups, makes it the norm rather than the exception for patrons who consume alcohol to do so far beyond the point of sobriety. That fact, by itself, is sufficient to create any legal responsibility to discontinue serving alcohol to those patrons, but in practice, that standard is hardly ever enforced, primarily because it would reduce sales directly as well as indirectly if patrons chose to drink at less responsible establishments. However, aside from the legal definition of intoxication, bartenders also know or should know that many (and sometimes most) of their patrons intend to drive after drinking.

Irrespective of whether or not it is recognized by current law, that realization, combined with the bartender's awareness of the realities of intoxication in relation to the risks associated with driving under the influence of alcohol gives rise to an objective moral (if not legal) duty to prohibit driving after consuming alcohol without regard to relative degrees of intoxication defined by law. The law prohibits drinking while driving completely irrespective of relative sobriety or intoxication defined by BAC levels and by field sobriety tests (FST) administered by government authorities. In the same manner, bartenders have a moral responsibility to prohibit drivers from drinking at their establishments and then driving. Practices could easily be envisioned whereby bartenders maintained a mandatory requirement for drivers to surrender the keys to their vehicles on entry and to subject them to breathalyzer tests as a condition for the return of their keys.

Patrons whose tests revealed any detectable BAC would, thereby, not be permitted to drive from the premises unless or until they provided a clean breathalyzer.

In principle, nothing would prevent such a voluntary system from...

Realistically, of course, it is virtually inconceivable to imagine that such restrictions would ever be implemented, because doing so would reduce sales revenue substantially in addition to decreasing patronage as long as less morally responsible bartenders were in operation within any reasonable proximity. In fact, as discussed, the general practice within the industry is that bartenders routinely ignore established legal principles of criminal law and the standards of civil liability for the sake of revenue. Therefore, it is extremely unlikely that the industry would ever voluntarily implement any restrictions for the sake of the public good that far exceed the formal requirements of law and the standards defined by theories of civil vicarious liability. That does not, however, detract from the purely moral responsibility of bartenders for harms caused by their providing alcohol to drivers.
Conclusion:

Current penal law and theories of civil liability hold bartenders criminally responsible and civilly liable (respectively) for the harms caused to others by their serving alcohol in excessive amounts to patrons who exhibit signs of intoxication.

Current law does not recognize their responsibility for harms caused by drivers whose intoxication is not outwardly obvious, despite the fact that obvious intoxication is not required for alcohol consumption to play a causative role in vehicular accidents involving drivers with lower BAC levels than necessary to meet the legal definition of "intoxication." However, moral responsibility transcends arbitrary numerical measurement of intoxication, creating a moral responsibility beyond that defined by law.

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