Cognitive and automatic functions: Alcohol has a stronger influence on cognitive functions, which include motor skills and concentration in activities like steering, braking, signal detection, hazard perception, reaction time, and hand-eye coordination.
Marijuana affects automatic functions. These include the ability to stay in the lane of traffic or to keep speed constant. Marijuana also degrades the ability to make decisions quickly, thereby affecting the ability to react to external cues like changing traffic signals or the presence of an obstacle in the road.
Over-and-underestimation of driving ability. Marijuana makes drivers more likely to underestimate their driving abilities. Pot smokers tend as a result to become more cautious and to engage in compensatory behaviors like driving more slowly and keeping a longer distance between themselves and vehicles ahead of them. This cautiousness can lead many marijuana smokers to consider themselves impaired even when they actually are not.
Alcohol has the opposite effect: drinkers are more likely to overestimate their abilities. Drivers with a .04 blood alcohol content level, for example, tend to believe that they are not impaired when in reality they are. Alcohol-intoxicated drivers tend to drive faster than they would if they were sober, and are more likely to attempt to overtake another vehicle ahead of them than marijuana smokers.
Use of marijuana and alcohol in combination. Combining marijuana and alcohol tends to bring out the worst effects of each of them on driving behaviors. Both cognitive and automatic functions are impaired, while the compensatory behaviors that marijuana-influenced drivers would otherwise use are overtaken by the greater risk-taking and overestimation of ability that drunk drivers display.
Although it may be tempting to conclude that marijuana may be “safer” to use than alcohol when it comes to driving, neither is in fact safe to use by itself, and taken together they create a worst-of-both-worlds effect that greatly increases the risks of negligent or even reckless behaviors that can contribute to car accidents and their resultant injuries, property damage and even death.
Those injured in a car accident may want to consult an attorney to better understand their rights, whether the culprit was under the influence or not, victims may be entitled to compensation.