Driver fatigue and highway driving: A simulator study

Abstract

Long duration of driving is a significant cause of fatigue-related accidents on motorways or major roadways. The fatigue caused by driving for extended periods acutely impairs driver alertness and performance and can compromise transportation safety. This study quantitatively measured the progression of driver fatigue and identified the conservative safe duration of continuous highway driving. Thirty young male subjects were analyzed during 90 min of laboratory-simulated highway driving. Sleepiness ratings (SSS) and reaction time (RT) tests were used to assess impairment of driver alertness and vigilance. Additionally, various measures of driving performance recorded throughout the experiment were used to measure temporal deterioration of driver performance from alert to fatigued using principal component analysis (PCA). The analytical results revealed that SSS scores, reaction times (RTs) and unstable driving performance significantly increased over time, indicating that excessive driving time is a significant fatigue factor and potential cause of fatigue-related accidents. Moreover, the analytical results indicated that 80 min was the safe limit for monotonous highway driving. Based on the experimental findings of this study, public awareness of the adverse affects of driver fatigue during long-distance driving should be enhanced. This study provides explicit information of fatigue development that can be used to prevent fatigue-related accidents.

Introduction

Driving is a vital daily activity throughout the world [1], [2]. However, driving at highway speeds requires significant cognitive and motor skills such as visual–spatial ability, memory, information processing and rapid reaction, all of which require mental alertness [3]. Driver fatigue is known to occur when driving requires sustained attention over long periods [4] and markedly impacts driver psychophysiology while driving. The deteriorating driver performance associated with driver fatigue presents a serious safety risk. Therefore, identifying significant indicators of fatigue is critical for improving driver safety on highways. Moreover, an explicit knowledge of fatigue limits can determine the intervals at which drivers should be advised to rest.

Methodological approaches for assessing the progression of fatigue are extremely varied. Fatigue has numerous causes, each with a specific incidence and relationship to traffic accidents. The factors most commonly associated with driver fatigue are monotonous environments, duration of driving, sleep deprivation, chronic sleepiness and drug and alcohol use [5], [6], [7], [8]. However, under typical driving conditions, time-on-task is a well-known fatigue factor adversely affecting driver safety. Many studies have demonstrated the association between time-on-task and fatigue progression using various subjective and objective methodologies [9], [10], [11], [12], [13], [14], [15], [16]. For instance, Kecklund and Åkerstedt [9] determined that subjective sleepiness level and electroencephalogram (EEG) spectral power (alpha and theta waves) increase significantly with driving time. Ranney et al. [11] in an analysis of subjects using a driving simulator, demonstrated that excessive driving time increases driver sleepiness and vehicle speed and decreases driver awareness of pedestrians. Van der Hulst et al. [13] determined that sleepiness scores (SSS) and standard deviation of the lateral position varied markedly during driving. Otmani et al. [16] also observed that frequency of right edge-line crossings significantly increase as driving time increases.

The risk of accidents significantly increases during prolonged driving; however, safe limits for continued driving are widely debated. According to prior descriptive analysis of highway accidents from police databases, various ecological factors are closely associated with the progression of fatigue and increase the incidence of fatigue-related accidents [17], [18], [19], [20], [21], [22], [23]. For instance, O'Hanlon and Kelly [24] considered driving in a monotonous environment is a vigilance task. The impaired performance caused by decreased vigilance may contribute significantly to vehicular accidents [25]. A high proportion of accidents occur on straight roads with homogeneous scenery [23], [24], [25], [26], [27]; long periods of monotony negatively impact driver alertness, vigilance and driving performance. Moreover, disruption of 24-h circadian rhythms or time of day also contributes to fatigue [28], [29]. Pack et al. [22] noted that a significant proportion of sleep-related accidents occur during the early morning (2:00–6:00) and afternoon (14:00–16:00). Due to circadian and homeostatic influences, human activity in the mid-afternoon and early morning significantly reduces alertness [14], [16], [17], [23], [30], [31]. Other studies indicate that young drivers (< 30 years) also account for a significant proportion of fatigue-related accidents [19], [22]. Due to their minimal experience and dynamic driving styles, young drivers, particularly males, are at a higher risk for accidents than more older and experienced drivers [16], [20], [21], [23].

Fatigue has been implicated as a primary cause of many accidents. The potential for fatigue-related accidents significantly increases during prolonged and monotonous driving [14], [18], [19], [23], [32], [33], [34]. Driver fatigue and its associated damage are important public safety issues [23], [24] and should be a focus of public education regarding the safe duration of highway driving; however, this area has been relatively neglected. To date, the only published study is Nilsson et al. [6], which utilized a subjective fatigue checklist for a 2.5-h simulated driving task and identified a nonlinear relationship between self-reported fatigue and driving time. Moreover, recent studies have noted that drivers typically underestimate the impact of driver fatigue, ignore feelings of drowsiness and continue driving when they become sleepy (Reyner and Horne [52]; Horne and Baulk [34]). Thus, this study utilized multi-objective and subjective measurements to quantify the progression of driver fatigue and identify a reasonable and safe limit for duration of highway driving.