During which phase of DUI detection is the vehicle in motion observed?

The correct answer is the first phase of DUI detection. During this phase, law enforcement officers observe the vehicle while it is in motion. This initial observation is critical as it helps officers identify potential signs of impaired driving based on the vehicle's operation. For instance, they look for erratic behavior such as swerving, speeding, or slow response to traffic signals. These observations set the stage for subsequent phases of detection, where officers may focus more closely on the driver and their demeanor once the vehicle is stopped. This phase often informs the officer’s decision to initiate a traffic stop or further investigate suspected DUI behavior.