Driving while impaired by alcohol or drugs - a charge that almost always runs as two separate cases at once, one criminal and one over the licence.
The names differ by state - driving under the influence, driving while intoxicated, operating while impaired - but the charge generally has two independent routes to a conviction. One is a measured blood-alcohol concentration at or above the legal limit, which requires no proof that the driving was actually affected. The other is impairment in fact, which can be established without any chemical test at all, and which is how drug-impairment cases are usually brought since there is no equivalent of a breath test for most substances.
The feature that surprises people most is that there are typically two proceedings, not one. The criminal case runs in court. A separate administrative case, run by the state licensing agency, deals with the driving privilege and is often triggered by the arrest or by refusing a chemical test rather than by any conviction. It moves on its own much shorter timetable, and the deadline to contest it can expire while the criminal case is still at its first hearing.
Refusing a test is not a neutral option. Every state operates an implied-consent scheme under which the licence itself is conditioned on agreeing to testing, so a refusal usually carries its own penalty - sometimes a longer suspension than a failed test would have produced - and the refusal can be used as evidence.
The administrative licence deadline is the reason this is time-sensitive rather than merely serious: it is frequently measured in days from the arrest, it runs whether or not anyone has been to court, and missing it forfeits the licence hearing regardless of how the criminal case later turns out. The technical questions - whether the stop was lawful, whether the testing device was properly maintained and operated - are also the kind that are difficult to raise without counsel.
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