Effects of coffee on driving performance during prolonged simulated highway driving

RATIONALE: Coffee is often consumed to counteract driver sleepiness. There is limited information on the effects of a single low dose of coffee on prolonged highway driving in non-sleep deprived individuals. OBJECTIVES: The aim of this study was to examine the effects of a single cup of coffee (80 mg caffeine) on simulated highway driving performance. METHODS: Non-sleep deprived healthy volunteers (n = 24) participated in a double-blind, placebo-controlled, crossover study. After 2 h of monotonous highway driving, subjects received caffeinated or decaffeinated coffee during a 15-min break before continuing driving for another 2 h. The primary outcome measure was the standard deviation of lateral position (SDLP), reflecting the weaving of the car. Secondary outcome measures were speed variability, subjective sleepiness, and subjective driving performance. RESULTS: The results showed that caffeinated coffee significantly reduced SDLP as compared to decaffeinated coffee, both in the first (p = 0.024) and second hour (p = 0.019) after the break. Similarly, the standard deviation of speed (p = 0.024; p = 0.001), mental effort (p = 0.003; p = 0.023), and subjective sleepiness (p = 0.001; p = 0.002) were reduced in both the first and second hour after consuming caffeinated coffee. Subjective driving quality was significantly improved in the first hour after consuming caffeinated coffee (p = 0.004). CONCLUSIONS: These findings demonstrate a positive effect of one cup of caffeinated coffee on driving performance and subjective sleepiness during monotonous simulated highway driving.