What is a common indication that a driver may be under the influence of drugs or alcohol?

Erratic behavior, such as swerving or sudden stopping, is a common indication that a driver may be under the influence of drugs or alcohol because these actions suggest a lack of focus or impaired judgment, which are both typical effects of substance use. When a driver is impaired, their ability to maintain a safe and consistent path on the road diminishes, leading to unpredictable maneuvers like swerving between lanes or making abrupt stops that are not related to normal driving conditions.

While excessive speed and rapid lane changes can also be signs of reckless driving behavior, these can stem from other issues such as aggressive driving rather than specifically from impairment. Using turn signals excessively might indicate confusion or even overly cautious behavior, which does not align with typical impairment indicators. Lastly, driving with headlights off, while unsafe, does not necessarily point to impairment; it may simply be a result of forgetfulness or inattention. Therefore, swerving and sudden stops are more directly linked to the effects of drugs or alcohol on a driver’s ability to operate a vehicle safely.