Alcohol, Drugs, and Driver Fitness
What the exam tests
Alcohol, Drugs, and Driver Fitness tests the CDL alcohol limit, drug prohibitions, and the driver's duty to avoid impairment from any source.
Core rules
- A CDL driver may not operate a commercial motor vehicle with an alcohol concentration of 0.04 or greater.
- Refusing a required alcohol or drug test is treated as a violation.
- Marijuana is prohibited under federal DOT rules, even if state law allows medical or recreational use.
- Prescription and over-the-counter drugs can impair driving; ask a doctor or pharmacist about effects and interactions.
- Fatigue, illness, and emotional stress also reduce fitness for duty.
Worked example
A driver has a 0.03 BAC after one drink and feels fine. The per-se CDL threshold is 0.04, but the driver should still not drive because alcohol can impair judgment and company policy may be stricter. The safe and defensible choice is to wait, arrange another driver, or stay off duty.
Traps that cost marks
Applying the 0.08 noncommercial limit, assuming state marijuana law controls, and ignoring a prescription drug warning. Another trap is thinking a refusal only matters if alcohol is found.
Key idea
Fitness for duty is judged before the wheels roll, not after a crash.