Question

why does a target bac help identify drunk driving?
it is easy to objectively measure target bac.
it is easy to objectively test loss of judgment.
it is easy to subjectively test loss of judgment.
it is easy to subjectively measure target bac.

Explanation:

BAC (Blood - Alcohol Concentration) is a measurable quantity. Measuring BAC is an objective process (using breathalyzers, blood tests etc.). Testing loss of judgment is more subjective (e.g., field sobriety tests which can be influenced by many factors like a person's physical condition, anxiety etc.). And BAC is measured objectively, not subjectively.

Answer:

It is easy to objectively measure target BAC.