Analysis of Subjective Sleepiness Considering the Influences of Driving Workload, Duration between Stations, and Driving Duration in Railway Driving

Abstract: Railway drivers are required to maintain wakefulness while driving to confirm that the area in front of their vehicle is safe and to cope with extraordinary events. However, the driving environment, which includes being alone in the cab and performing monotonous tasks, tends to induce sleepiness. Therefore, in this study, we analyzed subjective sleepiness to investigate the relationship between drivers’ sleepiness and driving conditions. This study aimed to identify the influences that the driving workload, duration between stations, and driving duration have on drivers’ sleepiness.We used a railway driving simulator to conduct the experiment. Thirty males participated in our study. The participants drove in two ways: (1) the participants controlled the velocity of the simulated train, referred to as “high driving workload,” and (2) the system controlled the velocity of the simulated train, referred to as “low driving workload.” The durations between stations included the following three conditions: 1.5, 3.0, and 5.5 minutes. The duration of stopping at a station was 0.5 minutes. After practicing, the participants drove under six experimental conditions, consisting of a combination of two kinds of driving workload and three durations between stations. We randomized the order of the experimental conditions for each participant. The driving duration was 18 minutes per experimental condition. At every minute while driving, the participants were required to rate their subjective sleepiness using the Karolinska Sleepiness Scale, with the following grades: “Extremely alert” (score = 1) and “Extremely sleepy – fighting sleep” (score = 9).We conducted a multiple regression analysis in which the objective variable was the mean of the subjective sleepiness score, and the explanatory variables included the driving workload (high or low), the driving duration after stopping at a station (from 0 to 5 minutes), and the total driving duration (from 1 to 18 minutes).The results of the multiple regression analysis revealed that the score of subjective sleepiness was significantly associated with the driving workload, the driving duration after stopping at a station, and the total driving duration. The findings from the partial correlation coefficient indicated that with all other variables being constant, subjective sleepiness increased by 1.52 when the driving workload was low compared with when it was high. Subjective sleepiness also increased by 0.16 when the driving duration after stopping at a station increased by 1 minute. Furthermore, subjective sleepiness increased by 0.06 when the total driving duration increased by 1 minute. Additionally, the standardized partial regression coefficient showed that the driving workload had the largest influence among the three variables.With regard to the influence of driving workload, a previous study in the automobile industry showed that reducing driving workload caused “passive fatigue,” leading to sleepiness. Our results also showed that a low driving workload induced sleepiness. Furthermore, in terms of the effect of the driving duration after stopping at a station, another previous study in the automobile industry referenced “highway hypnosis,” whereby the monotony of the road environment tended to induce sleepiness. Our results showed that a long driving duration after stopping at a station was thought to be monotonous. Additionally, with regard to the total driving duration, the previous study indicated that the levels of sleepiness increased during driving. Our results also indicated that sleepiness increased with a longer driving durations.

Keywords: Subjective sleepiness, Railway driving simulator, Multiple regression analysis

DOI: 10.54941/ahfe1006536

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