For a Colorado driver aged 21 or over, which blood alcohol concentration is the legal limit for driving?

Why A is correct

Colorado treats 0.08% as the per se limit for drivers aged 21 and over: at or above that concentration the driver is impaired as a matter of law, and the state does not have to prove sloppy driving separately. The number is lower for other groups — commercial drivers are held to 0.04%, and drivers under 21 fall under a far stricter zero-tolerance standard, so a single drink can put a teenage driver over the line. Alcohol absorption also continues after the last drink, which means a driver can be under the limit when they leave and over it twenty minutes later, and that is why there is no reliable way to drink to a number.

Why the other options are wrong

B. 0.04%

0.04% is the limit that applies to commercial drivers operating a commercial vehicle, not to someone driving an ordinary passenger car. Applying the commercial figure to a standard licence would make the limit twice as strict as the law actually requires.

C. 0.05%

0.05% is not Colorado's limit for any driver category. Picking it usually means remembering a figure from another state or another country; the adult per se limit in Colorado is 0.08%.

D. 0.02%

0.02% sits far below the adult limit. It is much closer to the zero-tolerance standard applied to drivers under 21, which is deliberately strict because any measurable alcohol in a young driver is treated as a serious violation.

On the road

A driver has two beers with dinner, feels completely fine, and drives home. On the knowledge test the question is not how the driver feels — it is whether the concentration has reached 0.08%. Because impairment begins well before that point, the only reliable plan is a rideshare, a sober driver, or waiting it out.

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