There may never be a way to regulate alcohol consumption at bars and restaurants until strict laws are enforced that hold bars and bartenders accountable for the results of over-serving. What about the excuse that there really is no way to tell because a patron who could have become drunk at home can just go to the bar afterwards? Don't let him or her in. If you question their sobriety, give them a quick breathalyser test and go from there.
If a maximum drink law can't really be enforced, then bars should come up with a system that keeps track of how many drinks a person was served. Allowing only one drink per person at a time when ordering is a start, but they should also figure out a way to count how many times that person has been to the bar. If they are held accountable for a drunk-driving death, how many would truly try to shut people off when they've had too much to drink? Probably more than currently engaging in this "mandatory" practice. Would there be less drunk driving? Probably. Would there still be alcoholism in the US? Definitely, but the roads would be safer, and maybe, just maybe, alcoholism would be less prevalent.

A picture of the car that an 18 year old boy was trapped in and burned alive as the result of a drunk driver. (www.duihope.org)

From www.duihope.org. A picture of a once beautiful girl whose face was crushed as a result of a drunk driver.