Driver's License Test Prep
Oregon Practice DUI & Impaired Driving

You've had a drink and used marijuana before driving in Oregon. According to the driver manual, what does combining the two substances do to your ability to drive?

  1. A.
    Driving is unaffected as long as your BAC stays under 0.08%.
  2. B.
    The combination can reduce your ability to drive safely. Correct
  3. C.
    Marijuana counteracts the alcohol, making driving safer than after drinking alone.
  4. D.
    Marijuana has little effect at the wheel because it metabolizes slowly, so the alcohol is the main concern.
The Why

The answer is "The combination can reduce your ability to drive safely."

The Impaired Driving section addresses the combination directly: the use of alcohol and marijuana together can reduce a person's ability to drive safely. Separately, the manual notes marijuana impairment has contributed to many collisions in Oregon, and that alcohol is the most common drug involved when drivers are impaired. Both substances impair driving on their own, and neither offsets nor cancels the other. The folk belief behind C, that one drug balances out another, gets no endorsement from the manual.

Why the others miss

The traps in the wrong answers

A. Driving is unaffected as long as your BAC stays under 0.08%.

The 0.08% threshold is the alcohol presumption of impairment, not a global "safe to drive" cutoff. The manual notes you can be arrested for DUII even with a BAC lower than 0.08%. This answer treats the BAC per-se number as a green light for any kind of impairment; the manual says you can still be arrested even if your BAC is lower than 0.08%.

C. Marijuana counteracts the alcohol, making driving safer than after drinking alone.

Neither substance offsets the other. The manual states the use of alcohol and marijuana together can reduce a person's ability to drive safely. This answer rests on the folk belief that one drug "balances out" another; the manual makes no such claim and instead warns that using the two together can reduce your ability to drive safely.

D. Marijuana has little effect at the wheel because it metabolizes slowly, so the alcohol is the main concern.

Marijuana actively impairs driving, and the manual says marijuana impairment has contributed to many collisions in Oregon. This answer confuses how long marijuana remains detectable in the body with how long it actively impairs; the manual treats marijuana as a real impairing drug, not an inert one.

The Rule

This question tests your knowledge of DUI & Impaired Driving in Oregon. Source: Oregon Driver Manual, "Impaired Driving," p.82..

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