Driving while impaired by alcohol or drugs is a serious problem, estimated to be linked to one-third of traffic deaths each year. So it's the target of increasing attention and enforcement. But that doesn't mean that every charge brought is valid, or that all law enforcement techniques are reliable (many aren’t) or will protect your legal rights.
Whether it's called ''driving under the influence'' (DUI) or ''driving while impaired'' (DWI), every state makes it a crime to drive while intoxicated by alcohol, and sets 08% blood alcohol content as a per se for drivers age 21 and above (lower benchmarks apply to commercial drivers and drivers younger than 21). Many states also recognize a lesser offense for those demonstrably impaired by alcohol, drugs, or a combination. The greater offense, usually called DUI, is typically a felony punishable by a year in jail; the lesser offense (usually DWI) a misdemeanor subject to several months in jail.
Besides imprisonment, a DUI conviction can also bring fines, and license suspension or limits, plus bring higher insurance premiums. It can affect some occupational licenses or immigration status. Repeat offenses, or driving on a suspended license, can bring heavier penalties, with significant jail time.
If You're Stopped by Police
Although the Constitution doesn't give you the right to drive (the state does by giving you a driver’s license), police stops or police actions after stops can’t violate the Constitution. Local police and other state law enforcement agents can take reasonable steps to enforce the law, but can’t violate the Fourth Amendment's bar on unreasonable searches and seizures. So there needs to be something to give the police a reasonable suspicion of a law violation (such as a missing taillight or a driver operating the vehicle in a way that reasonably suggests the driver may be DUI.).
The police will indicate you should stop (do so), then ask for your identification, registration and insurance information (provide it), and then question you (keep your hands in plain sight, and say nothing). You may be asked if you've been drinking (decline to answer, unless the honest answer is no). You’re within your legal rights not to answer, and if you have been drinking, you probably don't want to admit it. The police may ask you to perform some roadside ''field tests,'' like walking heel-to-toe, standing on one leg; or having your gaze follow a moving object. Bad news: they’re highly subjective and hard to pass, even if sober. Good news: you can also decline to take these.
Every state has a ''consent law'' requiring you to forfeit your driver's license if you refuse to take a breath or blood test. So if the police still suspect you're intoxicated, they may ask you to take a breath test on a portable breathalyzer, or arrest you and take you to the stationhouse for either a blood test or a breath test on a more sophisticated breathalyzer.Last summer, the U.S. Supreme Court decided three cases making clear state and local police must obtain warrants before performing blood tests for alcohol content, but they need not have a warrant before doing a breath test for alcohol.
If You're Charged with DUI
You may legal defenses (the police had no reason to stop you, or violated procedures) or factual defenses (like flawed tests or observations). Perhaps you were over your limit on drinks, but your charge could be reduced (by entering an alternative disposition program). For any of these, you'll need a competent, experienced DUI lawyer's assistance. Besides a criminal charge, you also have to deal promptly with an administrative proceeding to get your license reinstated.