Alcohol Effects on Drivers' Speed Management: The Influence of Visual Performance and Road Complexity

The aim of this work is to assess how drivers adapt their driving speed as a self-regulation mechanism when driving under the influence of alcohol, and the influence of alcohol consumption, visual performance, road complexity, and personal traits.

Thirty-one volunteers took part in the study. All of them underwent three experimental sessions: baseline (no alcohol), Alcohol 1 (low-moderate dose), and Alcohol 2 (moderate-high dose). Vision was tested using contrast sensitivity and retinal straylight. Driving performance was assessed using a driving simulator. The difference between the driving speed and the speed limit was calculated in 10 road scenarios of different complexity.

Drivers adapted their driving speed less (i.e., drove faster) in the Alcohol 1 condition compared with Alcohol 2 (p = .007). This indicates that participants felt more confident under the influence of a low-moderate dose of alcohol. Participants with better contrast sensitivity drove faster (p = .021). The complexity of the road and other factors such as driving experience, sex, or driving under the influence of alcohol frequency also influenced speed choice.

Drivers under the influence of a low-moderate dose of alcohol seem to be less aware of the risk. Contrast sensitivity is a good predictor of the speed choice when driving under the influence of alcohol. A better understanding of drivers' behavior under the influence of substance use may be useful to adjust and improve traffic laws and driving regulations.