As a Georgia DUI Lawyer, I have always had mixed feelings about whether a person should be arrested for a DUI after they voluntarily pulled over and stopped driving.
In practice, what happens is that the police come upon a parked car where they see someone sleeping inside it. They do a "safety check" to make sure that the occupant is okay. During the safety check, the police officer realizes that the person in the car is under the influence. Since the car did not drive itself (at least for now), the officer arrests the occupant for a DUI.
To me, when you arrest someone who chooses to stop driving when they know they are impaired, it creates an incentive to put others at risk.
Suppose someone begins to drive and realizes that they are unsafe to drive. As a society, we should want a person to pull over if they know they are under the influence. If someone knows that he or she is at risk of being charged with a DUI for sleeping it off in the car, we create an incentive for people to continue to drive, thereby putting the public at risk.
An Alternative Charge:
Georgia does not have a lesser offense DUI, as such that exists in other states. We should have our legislature pass a statute for the unsafe operation of a vehicle. It should be a non-arrestable offense, like most traffic tickets. I would suggest it should be Georgia's first 10-point offense.
In Georgia, anyone who accumulates 15 points will have their license suspended. Additionally, any person under the age of 21 will have their license suspended if they are convicted of an offense that carries 4 or more points.
The result is that for anyone under the age of 21, my proposed traffic offense would result in a license suspension. For adult drivers, my proposed law would likely suspend someone who has already accumulated points on their MVR.
However, what we would not be doing is sending people to jail who have made the better choice of not continuing to drive.