Why is the walk and turn test employed in a DWI assessment?

The walk and turn test is primarily employed in a DWI assessment to evaluate physical coordination and balance. This test requires the individual to walk heel-to-toe along a straight line, turn in a specific manner, and return to the starting point. These actions demand a degree of physical coordination and balance, which can be significantly impaired by alcohol consumption. Observing how well a person can execute this test provides law enforcement officers with valuable insight into the individual's level of impairment.

In contrast, factors cited in the other options, such as measuring a driver's speed, evaluating mental clarity, or checking for proper driving posture, do not capture the specific intent of the walk and turn test. Speed is more relevant to traffic violations and not the focus of sobriety testing. While mental clarity is assessed through other cognitive-based tasks, physical coordination and balance are what this particular test is designed to measure, reinforcing its role in assessing the effects of alcohol on motor skills.