Driver Drowsiness and Fatigue in the Safe Operation of Vehicles – Definition of Terms and Concepts
This Information Report provides definitions and discussions of key terms concerning driver drowsiness and fatigue, and basic information on measuring drowsiness and fatigue. It also includes information and concepts for driver drowsiness as they relate to safe operation of a vehicle. Examples of driver drowsiness and fatigue causal factors include those related to the following: (1) sleep quality and quantity, (2) time of day, (3) time on task (related to the task of driving), (4) task-related fatigue (arousal levels related to task underload and overload), and (5) combinations of these factors. Medical conditions, medication, alcohol or drugs exacerbate drowsiness; however, the discussion in this report is limited to fatigue concepts.
The Information Report has two primary sections: Section I provides definitions and discussions of key terms concerning driver drowsiness and fatigue; Section II provides basic information on measuring drowsiness and fatigue. This Information Report focuses on effects on the safe operation of a vehicle. These include the physiological and cognitive effects of driver drowsiness and fatigue on driving safety. Examples of effect of driver drowsiness and fatigue on driving safety include those related to vehicle control, vigilance, reaction times (object and event detection and response), situational awareness, physiological indicators, subjective assessments, and combinations thereof. For definitions of driving performance measures, see SAE J2944. This report applies to all worldwide motor vehicle passenger cars and light trucks; however, it can apply to heavy trucks, buses, motorcycles, and mopeds. The intended users of the document are practitioners and researchers in the automotive industry, academia, and other organizations with interest in driver drowsiness and fatigue, driving and driver performance assessment, and road safety.
Rationale: The terms “driver drowsiness” and “fatigue” are often used interchangeably; however, they are defined very differently. Drowsiness and fatigue are difficult to define and measure; therefore, it is difficult to assess and consequently regulate how to avoid driving while fatigued (National Academies of Science, Engineering, and Medicine, 2016). As fatigue is difficult to assess via post-crash reconstruction, estimates of the frequency and outcomes of fatigued driving are likely conservative (estimates are 10% to 20% of crashes). Drivers may be hesitant to disclose their level of drowsiness while driving, or the severity of the crash leaves the driver too incapacitated to report this information. Fatigued drivers are more likely to be involved in crashes and are more likely to be involved in higher severity crashes as drivers’ reaction times are often delayed and/or drivers have not initiated crash avoidance maneuvers (National Academies of Science, Engineering, and Medicine, 2016). Thus, there is a need for approaches that measure drowsiness and fatigue as it relates to the safe operation of a vehicle. This document provides a set of concepts and definitions of terms that can be used to measure drowsiness and fatigue.