Impairment

Alcohol consumption, which can impair the performance of a wide range of motor and complex mental functions, is a leading factor in many accidents because it decreases the ability of the drinker to process information and perform psychomotor skills (actions requiring hand to eye coordination). It also lowers the driver's cognitive ability. The amount of mental or physical impairment is directly related to the amount of alcohol consumed or the blood alcohol concentration of the drinker.

Alcohol impairment becomes especially critical for any individual operating a motorized vehicle due to the skills needed to maintain a car in the proper lane, monitor all environmental hazards, watch for other drivers and pedestrians and follow all traffic signals. Due to a driver's inability to divide their attention between multiple driving tasks, alcohol impairment commonly requires drives to favor one task over The amount of the impairment will vary based on the complexity of the task, the level of the driver's BAC and the speed at which the alcohol is eliminated from the driver's body.

The degree of impairment for drivers with the same BAC level can vary. Differences may occur for a variety of reasons including: the drinker's tolerance, their age, their food intake, their weight, their metabolism, their sex and their hydration level.

Field sobriety testing is frequently used to determine if a driver is driving under the influence of alcohol. Standardized field sobriety tests include the walk-and-turn test, the horizontal gaze nystagmus test and the one-legged-stand test. The standardized field sobriety test can be used to establish evidence that driver is intoxicated and allow the police officer to ask the driver to submit to a breathalyzer test.

Due to increased awareness and safety concerns, the government has begun imposing increased DUI penalties. DUI laws for most states now include per se laws which make it illegal for any driver to drive with a blood alcohol concentration of 0.08% or higher, regardless if there is evidence that they are mentally or physically impaired. The state argues that if the driver's BAC is this high this factor alone is an indicator of impairment.