Over 100 visual cues for spotting a drunk driver were compiled by the National Highway Traffic Safety Administration (NHTSA). This study was the result of extensive research and interviews of police officers making over 12,000 DUI (Driving Under the Influence) and DWI (Driving While Intoxicated) stops in the aggregate. Drivers can also use these cues to spot potentially dangerous drivers on the road who are likely to be driving while intoxicated. This can increase driver safety and also can be used as evidence in the event a car accident and personal injury occurs as a result of DUI / DWI.

Primary Signs of DUI / DWI / Drunk Driving

The signs of impairment contained in the NHTSA list help law enforcement predict whether a driver is likely to have a blood alcohol concentration (BAC) of 0.08% or greater through observation with the naked eye. At present, 0.08% BAC is the minimum BAC required to convict a driver of DUI / DWI in all states. The NHTSA breaks down the list of visual cues of DUI / DWI into are four major categories of driving behavior. Police officers believe that drivers who display these signs indicate at least a 35% chance of a motor vehicle operator being under the influence of alcohol.

• Problems maintaining proper lane position - failure to stay within one's driving lane on the road;
• Speed and braking difficulties - failure to maintain proper speed, sudden acceleration and braking;
• Vigilance problems - failure to pay attention to the surroundings and changing driving conditions;
• Judgment problems - inability to judge the road and proximity to objects, such as jerky or sharp turns, sudden movements and over-correction of steering.

Some individual factors, such as a driver weaving across the lanes on the road, indicate an increased probability of DUI or DWI to more than 50%. Combining most of these cues will usually indicate a likelihood of DUI or DWI to greater than 65%. There is an even greater chance of drunk driving when there are indications of swerving, sudden acceleration without cause and driving off of the road.

1. Problems Staying within a Driving Lane

Drivers who are intoxicated or otherwise impaired by the effects of alcohol experience difficulties with maintaining a consist and steady position within and moving between driving lanes. The most common DUI / DWI indicators include:

• Weaving through traffic and across traffic lane lines, perhaps even striking other vehicles or objects outside of the driving lane;
• Straddling the road side or center line (driving with one set of wheels on the wrong side of the line);
• Drifting towards one side of the road;
• Swerving, making abrupt turns in order to straighten out the vehicle;
• Making too wide a turn, drifting towards the outside of the turn radius.

2. Speed and Braking Difficulties

Impaired drivers usually have a difficult time with judging speed and distance while driving, including stopping properly. Common stopping problems that indicate DUI and DWI include:

• Coming to a stop at an odd angle
• Stopping the vehicle at a distance noticeably too far from the curb;
• Making stops too quickly, jerky and short stops;
• Stopping well before or beyond a limit line (such as a crosswalk).

Common acceleration related problems related to intoxication include:

• Sudden acceleration or deceleration without apparent reason;
• Varying levels of speed, consistently speeding up and slowing down, failure to maintain an even and consistent speed;
• Driving at a speed at least 10 or greater miles per hour below the speed limit.

3. Problems with Vigilance, Awareness of Driving Conditions

The failure to notice traffic conditions on the road, such as traffic control signals or the movement of other vehicles, is another good indicator of the presence of DUI or DWI. Drivers who display an overall lack of awareness that increase the likelihood of being impaired by alcohol include:

• Driving the wrong way or in the wrong direction;
• Slow responses to traffic control signals;
• Stopping or slowing down too quickly for no apparent reason;
• Using the wrong side turn signal when making turns or changing lanes;
• Driving in the dark without the headlights turned on.

4. Difficulties with Judgments While Driving

Driving a car, motorcycle, truck or other motor vehicle involves making a continuous set of judgments. A driver must be alert and able to properly gauge distance and speed. When under the influence of alcohol, drivers tend to be more flippant about taking risks. The following signs indicate an increased likelihood of DUI / DWI:

• Tailgating, following the vehicle in front too closely;
• Making illegal turns or driving in an improper lane;
• Unsafe or erratic lane changes (too slow or quick);
• Driving off of the road;
• Appearance of impairment, head drooping, falling to one side.

Visual Indicators of DUI / DWI After a Police Stop

The following are the most common signs of driver intoxication after being stopped by a police officer:

• Odor of alcohol, open containers of alcohol in the vehicle;
• Slurred speech,
• Slow response to questions, a need to repeat questions, failure to answer questions properly;
• Poor motor skills, fumbling with documents, difficulty getting out of the vehicle, leaning on objects;