摘要：We conducted a systematic review and meta-analysis of the literature examining the relationship between driving performance and engaging in secondary tasks. We extracted data from abstracts of 206 empirical articles published between 1968 and 2012 and developed a logistic regression model to identify correlates of a detrimental relationship between secondary tasks and driving performance. Of 350 analyses, 80% reported finding a detrimental relationship. Studies using experimental designs were 37% less likely to report a detrimental relationship ( P = .014). Studies examining mobile phone use while driving were 16% more likely to find such a relationship ( P = .009). Quasi-experiments can better determine the effects of secondary tasks on driving performance and consequently serve to inform policymakers interested in reducing distracted driving and increasing roadway safety. DISTRACTED DRIVING HAS emerged as a growing road safety concern, both in the United States and in other parts of the world. 1–3 The US National Highway Traffic Safety Administration reported that in 2009, almost 450 000 people were injured and 5500 died in motor vehicle crashes in which distracted driving was a factor. 4 People engage in distracted driving when they simultaneously operate a vehicle and participate in a nondriving activity that could divert attention away from the primary task of driving. 5,6 These nondriving activities are also referred to as secondary tasks . 7–10 In recent years, the use of mobile phones while driving has been a major concern. 11,12 Along with the exponential growth of mobile phone use in general, there has also been a steady increase in the proportion of people who engage in mobile phone use while driving 13 and a simultaneous increase in the number of motor vehicle crashes that have resulted from this behavior. 4 Thus, policymakers at the federal, state, and local levels have proposed and enacted legislation banning texting and talking on mobile phones while driving. 14,15 Although the focus on the use of mobile phones as a secondary task is warranted, many other activities, such as cigarette smoking, 16,17 eating, 18,19 listening to music, 20,21 talking to passengers, 22,23 and interacting with in-vehicle information systems 7,24 are also considered secondary tasks. Though many studies have reported a detrimental relationship between these secondary tasks and driving performance, some studies have found that engaging in certain secondary tasks is associated with a protective effect on driving performance. 25–28 For example, Engström et al. 26 found that the presence of passengers was protective in terms of crash risk for novice drivers, and Hing et al. 28 found that passengers were protective for older drivers. There is also conflicting evidence that engaging in secondary tasks has more of a detrimental association with driving performance among novice drivers. 29,30 Moreover, researchers operationalize driving performance in several different ways (e.g., lane deviation, following distance, braking time) 24,31–36 and perform driving assessments in different settings (e.g., real-world or naturalistic, simulated). 37–39 Additionally, the ways in which driving performance data are collected also varies. Some studies use self-reported measures of driving performance, 40,41 and others use technologically measured assessments of driving performance. 36,42 Given this heterogeneity in riskiness of secondary tasks, the different ways and settings in which driving performance is measured, and the wide array of scientific journals in which these studies are published, it is difficult for policymakers and researchers to keep up to date on current findings, to be aware of gaps, and to ascertain the level of evidence in this body of literature. The purpose of this study was to systematically review and meta-analyze the literature on the relationship between secondary tasks and driving performance. We specifically focused on articles that had both a secondary task component and a driving performance outcome component. Our work supplements previous reviews of the literature that focused narrowly on the use of mobile phones as the secondary task, 43–45 injuries as the driving performance outcome, 46 and the state of the literature published in 1 particular journal. 47 These previous reviews have provided detailed summaries of individual studies captured in their reviews. For example, McCartt et al. 43 provided substantive information on studies that examined the effects of phone use on simulated driving tasks and, separately, studies that examined the effects of phone use on real-world driving. Likewise, Collet et al. 44 provided detailed synopses on the effects of phone use on different driving outcomes, such as lane keeping, vehicle speed, and headway. None of the previous literature reviews examined the outcomes of various secondary tasks in concert and thus could not identify, for example, whether 1 secondary task could be tagged as more detrimental than the others. In our study, we were generally interested in the prevalence of studies reporting a detrimental relationship between various secondary tasks and various driving outcomes. Moreover, we were interested in determining whether studies examining cell phone use as a secondary task produced dissimilar findings relative to studies examining other secondary tasks. Also, given the general belief that younger drivers are more inclined to engage in secondary tasks, we were interested in determining whether studies that focused on adolescents were more likely to find a detrimental relationship between driving performance and secondary tasks. Overall, our study aids in identifying gaps in the literature and provides a more comprehensive synopsis for policymakers, researchers, and other stakeholders interested in reducing the occurrence of distracted driving and its detrimental consequences.
