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

Objective: 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.

Method: 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.

Results: Drivers adapted their driving speed less (i.e., drove faster) in the Alcohol 1 condition compared with Alcohol 2 ( = .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 ( = .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.

Conclusions: 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.