While state DUI laws vary, most states prohibit driving with a blood alcohol content (BAC) is greater than .08 grams of alcohol per deciliter of your blood, OR while under the influence of any drug, or alcohol. Many people operate a vehicle relatively soon after drinking (like after last call when the bar closes) and do not have a BAC greater that .08, and are not under the influence of alcohol.
A person who has consumed a small quantity of alcohol, is not driving while
impaired, and who does not have a BAC greater than .08, can still be in
the uncomfortable position of being investigated for DUI because of a
traffic infraction unrelated to DUI.
After a traffic stop, an officer cannot detain the motorist for a period of time longer than necessary to investigate the traffic offense for which the motorist was pulled-over. However, most law enforcement officers pick up on alleged "indicators of impairment" causing them to expand the traffic stop into a DUI investigation. This includes bloodshot eyes, slurred speech, an odor of alcohol coming from the vehicle, the driver seeming to be disoriented, and an admission to drinking by the driver. Sometimes the traffic offense is an indicator of impaired driving, e.g. swerving back and forth across the lanes.
Many of these cues can be caused by situations other than alcohol consumption, e.g. allergies, having contact lenses in too long, and being tired. Although there is no correlation between the amount of alcohol consumed and the strength of the odor of alcoholic beverage coming from the breath, it is not hard to imagine how someone with allergies, who had a long week of work, and has a beer with that dinner, can get pulled over for failing to signal a turn and find himself deep in the middle of a DUI investigation.
Although the cues identified above are likely to give the officer enough
evidence to detain the motorist for additional questioning related to
a DUI investigation, these cues standing alone would probably not support
an arrest of the suspect for DUI. Therefore, the officer will engage in
further investigation, such as asking where the suspect has been, asking
how much the suspect had to drink, and having the suspect engage in field
sobriety tests. This additional investigation is designed to gather more
evidence in order to establish "probable cause" to arrest the
suspect for DUI.
In most states the motorist does not have to answer any questions about their travels, their alcohol consumption, and does not have to perform field sobriety tests. The Fifth Amendment to the United States Constitution protects individuals from being forced to give incriminating statements to law enforcement.
Failing to cooperate with answering those questions and refusing to participate
in the field sobriety tests will leave the officer with having to determine
whether there is enough evidence to detain the suspect for a preliminary
breath test, or to let the motorist go. Most likely, a preliminary breath
test will be administered. (The preliminary breath test is an informal,
hand held test for alcohol in the breath administered by the officer on
the scene of the traffic stop.) While the penalty for refusing such a
test is generally small, it is still a crime to refuse this test in many
states. The motorist who has had very little to drink is unlikely to "fail"
the preliminary breath test, and the officer will probably not arrest
that suspect. If the suspect refuses the preliminary breath test, which
is an arrestable offense, the formal test of the person's blood or
breath conducted later in the investigation will probably not result in
a BAC greater than .08 if the suspect only consumed a small amount of
alcohol. Therefore, the suspect will probably not be cited for DUI, (although
in such a scenario, there may be charges for refusing the preliminary
In the unlikely event the suspect fails the preliminary breath test, they will likely be arrested for DUI. However, the lack of evidence concerning how much the suspect drank, where they drank, and how they performed on field sobriety tests will assist their attorney at efforts to have the arrest suppressed (and the charges thrown out). Further, on the more sensitive formal test, the suspect who truly had a minimal amount of alcohol is unlikely to provide a test sample greater than .08. And because proving beyond a reasonable doubt that driving ability was simply impaired due to alcohol consumption in the absence of a test result greater than .08 is a difficult task, this motorist probably will not be charged with DUI.
The best course of action is to not drink and drive. However, most people who go out to dinner and have a drink do not wait for the alcohol to metabolize and dissipate. Thus a person who has not consumed enough alcohol to be above the legal limit may still be arrested for driving under the influence. An experienced criminal defense lawyer can fight these charges for you.