Prohibited Practices and Driver Distraction
Domain 5 tests the conduct rules that disqualify drivers fastest: phones, texting, alcohol and drugs, smoking, and unauthorized people aboard.
Phones and texting
Federal rules prohibit texting while driving a CMV (49 CFR 392.80) and handheld mobile-phone use while driving (392.82). Hands-free is allowed only with a single-button or voice-activated start, and the device must stay within reach without unbuckling. A red light is still driving. If you must talk or text, pull off the road legally first. Penalties reach thousands of dollars for the driver and the carrier, and repeat offenses bring disqualification.
Alcohol and drugs
The CMV limit is 0.04 BAC; any alcohol within four hours of coming on duty is prohibited, and refusing a test is treated as a positive. Marijuana - medical or recreational, even where state law allows it - and CBD products remain prohibited, as do impairing prescriptions.
Smoking and unauthorized riders
Smoking is prohibited aboard interstate passenger-carrying vehicles (49 CFR Part 252) and the carrier must post signs; state and local rules may be stricter, and there is no smoking during fueling. Only authorized people ride: no hitchhikers, no friends along for the trip, no one else at the wheel, and no passenger in the driver's area while you are moving.
Worked example
A driver's random test reads 0.03 - under the 0.04 limit, but still a violation because he drank two hours before duty. He is removed from safety-sensitive duty and the result is reported; under the limit is not a defense to the four-hour rule.
Traps
Believing hands-free means holding the phone on speaker; assuming state-legal marijuana is acceptable; thinking a short text at a red light is safe; allowing a rider to stand beside the driver.