Injuries are not accidents, so in public health we search for their causes to improve prevention. The best of these efforts seek to identify root causes, avoiding the more limited approach that stops at the level of "the human" responsible for "the error." Attention is directed to the variety of systems-related determinants that permit or promote human error--a root cause analysis resulting in a robust understanding of injury causality. As these root cause analyses move further upstream past a focus on individuals into systems, cultures, and societies, we have learned that the prevention of the majority of injuries depends much more on understanding organizational rather than individual factors. The importance of the interaction between the environment and the individual at risk in injury prevention is clear, particularly in the work environment. Advances in understanding and prevention of occupational injuries have resulted in a reduction in reported workplace injuries over the last 20 years in the United States. This suggests that intervention efforts have made a difference, although uncertainties in injury counting, underreporting, transformation to a service-based economy, and increased forms of poorly monitored contract and contingent work affect confidence in true progress. Although much has been gained by classifying and studying injuries according to the proximate location or event associated with the injury (motor vehicle, home, leisure time, workplace), this focus may limit inquiries too narrowly. Rigid classification forces a possibly misguided effort to identify only driver or road causes for motor vehicle accidents, or only home environment or family stressor causes for home-based injuries. This narrow view may inappropriately focus attention on work injury causes exclusively to workplace factors. Workers, healthy or injured, live and function in a broader environment than the workplace. Exposures and conditions at work can have a profound effect on out-of-work injury; similarly, home and community factors may increase or reduce the risk of injury at work. One example is provided by attention to prevention of road traffic injuries (RTIs). Hyder et al. (p. 1061) report that "RTIs will be 1 of the 3 leading contributors to the global burden of disease . . . over the next 2 decades." Efforts to address this problem are commendable. However, in the United States, RTIs are rarely considered occupational in origin, yet commuting time should be tied to work, and RTIs associated with commuting should be seen in light of increasing commuting time. Patterns of affordable housing distant from employment opportunities in many urban areas directly influence commute time (Lipman BJ. A Heavy Load: The Combined Housing and Transportation Burdens of Working Families. Washington, DC: Center for Housing Policy; 2006), increasing exposure to RTI risk. In addition, long work hours, double-shifts and two jobs are associated with a higher level of fatigue that results in less attentive driving under any circumstances (Akerstedt T, Philip P, Capelli A, Kecklund G. Sleep loss and accidents: work hours, life style, and sleep pathology. Prog Brain Res. 2011;190:169-188). Furthermore, some work-related stress could be leading to increased alcohol consumption (Frone MR. Work stress and alcohol use. Alcohol Res Health. 1999;23:284-291; Dawson DA, Grant BF, Ruan J. The association between stress and drinking: modifying effects of gender and vulnerability. Alcohol Alcohol. 2005;40:453-460) to "relieve" stress that, in turn, is associated with RTI risk. Elements of work-related fatigue, stress-relieving alcohol consumption, and poor public transportation alternatives all need to be incorporated in any systems view of RTI prevention. But if we don't begin by considering commuting a part of "work" then attention to work-associated mutable elements of the risk equation will continue to be ignored. Beyond RTIs we should consider what, if anything, is gained by drawing a line between work and nonwork injuries. Is an injury associated with an accident at home a home injury or a work injury, if analysis of the injury circumstances identifies work stress or work-related fatigue as the cause? Is an injury at work a work injury or a home injury if analysis of the injury circumstances identifies distraction due to a sick child as a contributing cause of the injury? Although in the United States workers' compensation systems force a determination as to whether an injury is occupational, this artificial creation of a bright line between work and out-of-work should not be allowed to interfere with good research and effective preventive interventions. Ultimately, a comprehensive, integrated approach to investigation of injury causation will result in more complete knowledge, the identification of promising areas for intervention, andmore effective prevention.