What indicates that a driver is under the influence of alcohol?

Difficulty maintaining lane position is a strong indicator that a driver may be under the influence of alcohol. Impairment from alcohol can affect a person's coordination, judgment, and reaction times, leading to swerving or drifting within their lane. These challenges in controlling the vehicle can be a clear sign of impaired driving.

In contrast, driving over the speed limit, while unsafe, is not exclusively indicative of alcohol impairment, as it can result from various factors including impatience or distraction. Turning on headlights is also a normal driving behavior that does not suggest impairment. Stopping at all traffic signals demonstrates compliant driving behavior, which does not correlate with being under the influence. This emphasizes the importance of observing lane discipline as a critical behavior for determining a driver's state while on the road.