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Driving under the influence refers to operating a motor vehicle after consuming too much alcohol or other illegal drugs. Driving under the influence, also referred to as DUI, driving while intoxicated or DWI, is illegal because it is dangerous and can lead to an increased chance of car crashes. A person found guilty of a DUI may be subject to criminal penalties.
Almost every country has some type of DUI or DWI laws, although these laws vary by jurisdiction. The laws are designed to prevent behavior likely to harm other drivers. Thus, they are public safety and health laws.
In most cases, driving under the influence covers only alcohol and illegal drugs. A person who takes a legal prescription medication and drives is generally not going to be found guilty of driving under the influence, unless the drug was abused or it specifically prohibited driving, for example.
The laws that prohibit DUI or DWI have established threshold levels of a drug or alcohol that must be in a person's system before he can be found guilty of the offense. For example, to be found guilty of driving while under the influence of alcohol in the United States, a person's blood alcohol level (BAC) must be .08 or higher. A person below the legal drinking age, however, can be found guilty of a DUI if he has any BAC at all, since he is not legally permitted to drink.
Generally, the levels of prohibited substance are set because those are the levels at which a person's reflexes are inhibited. Protection from accidents caused by inhibited reflexes or affected reasoning skills is one of the main reasons for the existence of DUI laws. When it comes to illegal drugs, in some jurisdictions, evidence of any amount of drugs is enough to impair judgment.
DUI laws are generally enforced by police officials. If a police officer believes a person is driving under the influence based on circumstantial evidence, such as the car weaving or displaying other erratic or unusual behavior, the police officer can pull the driver over. The driver then may have to submit to a series of field sobriety tests, such as a breathalyzer to detect blood alcohol content. If a person gets into a crash, his blood may also be tested to determine if he was under the influence of alcohol or narcotics at the time.
Penalties for driving under the influence vary by state and by the nature of the behavior. Loss of a license or fine is common. In some cases, jail time and even criminal sanctions are appropriate.