Alcohol, Drugs, and Distracted Driving
What this domain covers
Alcohol, drugs, and distracted driving questions test legal limits, implied consent, and the driving behaviors that raise crash risk. Missouri treats driving as a consent-based privilege: by driving, you agree to submit to a chemical test when an officer has reasonable grounds to believe you are impaired.
Core rules
For drivers 21 and older, the legal BAC limit is 0.08%. For commercial drivers it is 0.04%, and for drivers under 21 Missouri's zero-tolerance limit is 0.02%. A DWI can be proved by impaired driving even below 0.08% if drugs, alcohol, or a combination makes you unable to drive safely. Refusing a chemical test can lead to revocation of your license for at least one year, even if you are not convicted of DWI. Open containers of alcohol are prohibited in the passenger area of a moving vehicle. Prescription and over-the-counter drugs can support a DWI if they impair you. Missouri's hands-free law bars physically holding or supporting a phone and texting while driving; voice-operated or hands-free use is allowed. Fatigue and emotional distraction are also dangerous and are not cured by rolling down a window.
Worked example
A 20-year-old driver is stopped with a BAC of 0.03%. The reasoning: the adult limit is 0.08%, but the under-21 limit is 0.02%, so 0.03% is over the zero-tolerance threshold. The driver faces an under-21 alcohol violation even though an older driver at the same BAC would not be over the adult limit.
Traps
Thinking coffee, a cold shower, or fresh air sobers you up; assuming a prescription drug is safe to drive with; and believing a refusal to test avoids consequences. Also, holding a phone at a red light can violate the hands-free law.