Alcohol, Drugs, and Impaired Driving
Impaired-driving questions are heavily weighted because the consequences are severe. Kentucky uses per se limits, implied consent, and zero tolerance for young drivers.
Limits and consequences
For drivers 21 and older, a blood alcohol concentration (BAC) of 0.08 or higher is DUI per se. For drivers under 21, the limit is 0.02 - effectively zero tolerance. Commercial drivers are at 0.04. Kentucky's implied consent law means that by driving, you agree to a chemical test; refusing can lead to license suspension even if you are not convicted of DUI. DUI applies to alcohol, drugs, and any combination that impairs driving, including prescription medication.
What impairment does
Alcohol reduces judgment and reaction time before you feel drunk. It also causes tunnel vision and poor speed perception. Coffee, cold showers, and food do not speed elimination; only time does.
Worked example
A 20-year-old driver is stopped with a BAC of 0.03. Reasoning: the adult limit is 0.08, but the under-21 limit is 0.02. At 0.03 the driver is over the zero-tolerance threshold and can be charged with DUI even though an adult at the same BAC would not be per se impaired.
Traps
Believing one drink is always safe; assuming a prescription drug is legal to drive on; refusing the test to avoid a DUI - refusal has its own suspension; and thinking a night's sleep always clears alcohol. Kentucky also restricts open containers in the passenger area.