Many people who are subjected to a traffic stop by a cop after drinking alcohol unknowingly incriminate themselves when they represent (or more often than not misrepresent) their drinking history. Despite the fact that it is common that social drinkers will leave a bar or restaurant shortly after they finish drinking and begin driving within minutes of drinking, when stopped by the police a common response to the question of how much you had to drink is “two beers hours ago.”

First off it is should be noted that motorists are being detained or seized by the police when they are being questioned about their drinking history. And the question is designed to elicit incriminating information. Nevertheless courts are reluctant to hold that the circumstance constitutes “custodial interrogation,” which is the legal scenario which gives rise to the necessity that officer’s read a suspect his or her “Miranda rights.” So the fact that cop didn’t tell you that “you have the right to remain silent” in most cases will not be grounds to have your statements excluded from court.

At trial the prosecutor will use the time the suspect claims to have drank the alcohol as evidence to support the theory (more accuracy described as speculation) that the suspect drank much more alcohol than reported. This is how they do it: assume the suspect’s chemical test reflected a BAC estimate of .10 and the suspect told the police officer that he hadn’t drank for several hours before driving. The prosecutor will have the crime lab’s toxicologist estimate how much alcohol the suspect would have had to drank at that earlier point in time for the client’s blood alcohol level to be a .10 at the time of the chemical test. Since a person’s alcohol first rises and then falls after drinking and tends to disapate or “burn off” at a rather constant rate, that burn off rate will be used to estimate the number of drinks the suspect must have had several hours prior to being tested for alcohol.

The toxicologist’s estimate of how many drinks the suspect had consumed would have been different had the suspect informed the officer that he just finished drinking minutes before driving. Since recent drinking is consistent with a person’s blood alcohol level rising, it is more likely that the person’s blood alcohol level would be actually lower at the time of driving than it was at the time the chemical test. There is no crime of having a BAC of .08 after driving; only when it is proven beyond a reasonable doubt that your BAC was .08 at the time driving are you guilty of a DUI.