• The driver's ability to safely operate the vehicle is impaired by the effects of alcohol, illegal drugs, prescribed medications such as painkillers, or even over-the-counter medications such as antihistamines; or
• The driver is intoxicated at a level above established DUI standards, such as blood-alcohol concentration (BAC).

When a law enforcement officer makes a vehicle stop and suspects that the driver may be intoxicated, the officer will conduct a "field sobriety" test on the driver, and may ask for his or her consent to some form of chemical test for intoxication.

Field sobriety tests usually involve a police officer asking a driver to perform a number of tasks that assess any impairment of the person's physical or cognitive ability. Examples of field sobriety tests include having the driver walk a straight line, heel to toe; having he or she recite the alphabet backwards; and the officer's use of the "horizontal gaze nystagmus" (eye and penlight) test.

Chemical tests can be conducted during the vehicle stop, using a Breathalyzer that measures a driver's blood-alcohol concentration (BAC), or at a hospital, where urine and blood tests can be performed. Many states allow a driver suspected of DUI to choose which type of chemical test is administered.

All states have "implied consent" laws that require vehicle drivers to submit to some form of chemical test, such as breath, blood, or urine testing, if suspected of DUI. The logic behind such laws is that, by assuming the privilege of driving a vehicle on state roads and highways, drivers have effectively given their consent to DUI testing when a police officer reasonably believes the driver is under the influence of alcohol or drugs. If a driver refuses to submit to such testing, implied consent laws carry penalties such as mandatory suspension of a driver's license, usually for six months to a year. Often, license sanctions for test refusal are more harsh than those imposed after DUI test failure. In most states a driver's refusal to submit to a chemical test may be used to enhance the penalties imposed if he or she is eventually convicted for DUI.

All states have DUI laws that deem "per se intoxicated" any driver with a blood-alcohol concentration (BAC) above a set limit. In states like California and New York, this means that drivers with a BAC at or above .08 are intoxicated in the eyes of the law, and no additional proof of driving impairment is necessary.

All states also carry "zero tolerance" laws that target drivers under the legal drinking age. These laws penalize persons under 21 for operating a vehicle with any trace of alcohol in their systems (a BAC above 0.0), or with negligible BAC levels such as .01 or .02.

Keep in mind that a driver may still be arrested and convicted for DUI without proof of "per se" intoxication, when other evidence of impaired driving is shown. For example, a driver with a .06 BAC level can be found guilty of DUI if an arresting law enforcement officer testifies that he observed the driver's vehicle swerving badly, and that the driver exhibited both slurred speech and severe inattention during questioning after a vehicle stop.

A DUI conviction may carry criminal penalties including fines, jail time, probation, and community service. Some state laws impose certain minimum penalties for first-time offenses, then designate increased penalties for each offense thereafter. Severity of criminal penalties will vary according to the circumstances of the offense, including:

• Whether the driver has a history of DUI violations;
• Whether the driver was operating a commercial vehicle at the time of the DUI;
• Whether the DUI violation occurred while there was a child in the vehicle;
• Whether the DUI violation occurred simultaneously with another dangerous moving violation, such as reckless driving;
• Whether the DUI violation involved a car accident in which property damage occurred;
• Whether the DUI violation involved a car accident in which another person was injured or killed; and
• Whether the driver was under the legal drinking age at the time of the DUI violation.

In addition to potential criminal penalties, a DUI arrest or conviction will have an immediate negative impact on driving privileges.

Most state laws allow a motor vehicle department to immediately suspend the driver's license of any person operating a vehicle with a BAC above the state limit for intoxication, or any driver who refuses to submit to BAC testing. The driver's vehicle may also be confiscated or impounded, and the DUI offender will likely incur significant administrative costs. This loss of driving privileges can normally occur even before a DUI conviction. Most states allow a DUI arrestee to obtain a temporary license and request an administrative hearing at which he or she may argue against license suspension, or for restoration of limited driving privileges.

As with criminal penalties, the impact of a DUI arrest or conviction on driving privileges will vary according to the driver's history of DUI violations and the severity of the offense. An increasingly popular DUI penalty, especially for repeat offenders, is mandatory installation of an "ignition interlock" device on the offender's vehicle. This breath-testing device measures the vehicle operator's BAC, and will prevent operation of the vehicle if more than a minimum amount of alcohol is detected, such as BAC level of .02. Where this punishment is utilized, most states require the DUI offender to pay costs of installation, rental, and maintenance of the ignition interlock device. Rental fees alone can amount to as much as three dollars per day, so a DUI offender's expenses can add up quickly when an ignition interlock device is required.

Due to recent law enforcement trends that focus on preventing DUI by penalizing offenders harshly, most district attorney offices refuse to negotiate plea bargains in DUI cases. This is especially true if evidence of the violation is strong. In fact, many states have enacted laws that prohibit government attorneys from entering into plea bargains with DUI defendants. However, in rare cases a DUI charge may be reduced to a lesser offense like reckless driving or an "open beverage" violation.

Getting an Attorney's Help in a DUI Case

If you or a loved one are arrested for DUI, you may need the assistance of an experienced DUI defense lawyer. Unlike civil law cases, in which money or property may be at stake, people charged with DUI may face jail time and driver's license revocation. A skilled attorney who specializes in defending DUI cases will evaluate all the evidence, including the procedure and results of any field sobriety and chemical tests, to ensure that your legal rights are protected.

How drunk or high does someone have to be before he can be convicted of driving under the influence?

In most states, it's illegal to drive a car while "impaired" by the effects of alcohol or drugs (including prescription drugs). This means that there must be enough alcohol or drugs in the driver's body to prevent him from thinking clearly or driving safely. Many people reach this level well before they'd be considered "drunk" or "stoned." States vary as to the blood alcohol content (BAC) level that constitutes a DUI (driving under the influence) or DWI (driving while intoxicated).

How can the police find out whether a driver is under the influence?

Police typically use three methods of determining whether a driver has had too much to be driving:

• Observation. A police officer will pull you over if he notices that you are driving erratically -- swerving, speeding, failing to stop or even driving too slowly. Of course, you may have a good explanation for your driving (tiredness, for example), but an officer is unlikely to buy your story if he smells alcohol on your breath or notices slurred words or unsteady movements.
• Sobriety tests. If an officer suspects that you are under the influence, he will probably ask you to get out of the car and perform a series of balance and speech tests, such as standing on one leg, walking a straight line heel-to-toe or reciting a line of letters or numbers. The officer will look closely at your eyes, checking for pupil enlargement or constriction, which can be evidence of intoxication. If you fail these tests, the officer may arrest you or ask you to take a chemical test.
• Blood-alcohol level. The amount of alcohol in your body is understood by measuring the amount of alcohol in your blood. This measurement can be taken directly, by drawing a sample of your blood, or it can be calculated by applying a mathematical formula to the amount of alcohol in your breath or urine. Some states give you a choice of whether to take a breath, blood, or urine test -- others do not. If you test at or above the level of intoxication for your state (.08 to .10 % blood-alcohol concentration, depending on the state), you are presumed to be driving under the influence unless you can convince a judge or jury that your judgment was not impaired and you were not driving dangerously. Defense attorneys often question the validity of the conversion formula when driver's alcohol levels are based on breath or urine tests.

Do I have to take a blood, breath, or urine test if asked to do so by the police?

You may refuse to take a chemical test (blood, breath, or urine), but almost every state has a so-called "implied consent" law, and, under such laws, a refusal can result in suspension of your driver's license from anywhere between three to 12 months. (This is true even if you're eventually found not guilty of the current drunk driving charge.) Further, if your drunk driving case goes to trial, the prosecutor can tell the jury that you wouldn't take the test, which may lead the jury members to conclude that you refused because you were, in fact, drunk or stoned.

If I'm stopping for driving under the influence, am I entitled to talk to an attorney before I decide which chemical test to take?

The answer depends on where you live. In California, for example, you don't have the right to speak with an attorney first. But some states, including Arizona, allow you to talk to your lawyer before you take a chemical test.

If I'm stopped for driving under the influence, can a police officer ask me questions without reading me my rights?

Sometimes. The answer depends on whether or not you are in police custody -- that is, whether you are subject to the restraints common to a formal arrest. For example, the U.S. Supreme Court has ruled that the police do not have to provide Miranda warnings during roadside questioning of a motorist detained pursuant to a traffic stop. Thus, roadside questioning about your drinking, drug-taking, or performance on field sobriety tests does not constitute "custodial interrogation." However, once you are arrested -- or restrained by the police in a manner consistent with arrest -- you must be read your Miranda rights.

I've been charged with drunk driving. Should I get a lawyer?

Defending against a charge of drunk driving is a tricky business. Defenders need to understand scientific and medical concepts, and must be able to question tough witnesses, including scientists and police officers. If you want to fight your drunk driving charge, you're well advised to hire an attorney who specializes in these types of cases.

On the other hand, these days it's hard to "win" a drunk driving case, assuming the police gathered some physical evidence against you (results of a breathalyzer, blood test, or urine test). And the punishments for DUI are pretty standard. If you were truly guilty, it's unlikely that a lawyer could get you any better of a deal or plea bargain than you can get for yourself.

I was pulled over at a roadblock and asked to wait and answer a police officer's questions. Is this legal?

Yes, as long as the police use a neutral policy when stopping cars (such as stopping all cars or stopping every third car) and they minimize any inconvenience to you and the other drivers. The police can't single out your car at a roadblock unless they have good reason to believe that you've broken the law.