This is certainly not an endorsement of drinking and driving, regardless of how sleepy you may or may not be. If such laws have any benefit, and this is questionable, certainly a different closing time would seem to make more sense. Many believe that it is. Alcohol does hasten the onset of sleep, especially in those who have trouble falling asleep. But the fact is that alcohol causes disturbances to sleep, especially 3 to 4 hours into a nights sleep.
Normal sleep occurs in a series of cycles.
We have several different kinds of sleep. Each of these cycles is important to proper functioning during waking hours, especially REM and deep sleep. Alcohol disturbs the rhythms of these cycles, causing us to miss out on the benefit of these sleep cycles. The consequences for those who drink themselves to sleep are exactly what they are usually trying to avoid. During the second half of sleep, sleep is lighter, and those who drink are prone to awakening, and in having trouble returning to sleep.