Evaluating the Impact of Whole-Body Vibration (WBV) on Fatigue and the Implications for Driver Safety

Abstract

Driver fatigue is a significant contributor to motor vehicle accidents and fatalities, although the exact share of those events attributable to fatigue is still uncertain. In 2013, accidents involving heavy trucks killed more than 3,944 people in the United States, with over 80 percent of those killed not in the truck. Numerous factors contribute to driver fatigue among commercial drivers, including shiftwork schedules; high prevalence of alcohol and substance use; extended hours; comorbid medical conditions, such as pain; and high prevalence of sleep disorders. Many of these factors have been studied extensively in the trucking industry. Whole-body vibration (WBV) is another potential factor that may contribute to driver fatigue, but it has received little attention. Beginning in January 2015, Bose Corporation and AIG commissioned the RAND Corporation to study the link between WBV and driver fatigue. This article summarizes the findings from RAND's systematic review of the literature on WBV and fatigue as well as considers appropriate study designs and methodology that will inform new areas of research focused on improving the safety of truckers and those who share the road with them. The literature review identified 24 studies examining the impact of WBV on fatigue or sleepiness. The majority of studies (n = 18) found a significant association between WBV and fatigue or sleepiness; however, there are several limitations of the existing literature that preclude definitive conclusions regarding the impact of WBV on these outcomes. This research concludes with recommendations for future studies to strengthen the evidence base.

Driver fatigue is a significant contributor to motor vehicle crashes and fatalities, although the exact share of those events attributable to fatigue is still uncertain. We do know that, in 2012, crashes involving heavy trucks killed over 3,944 people in the United States, over 80 percent of who were not in the truck (National Highway Traffic Safety Administration, 2015). Thus, fatigue is a critical issue not only for driver safety, but for public safety in general. There are numerous factors that contribute to driver fatigue among commercial drivers, including shiftwork schedules; high prevalence of alcohol and substance use; extended hours; comorbid medical conditions, such as pain; and high prevalence of sleep disorders (Filiatrault et al., 1999; Lal and Craig, 2001; Sieber et al., 2014; and Teran-Santos et al., 1999). Many of these factors have been studied extensively in the trucking industry (Crum and Morrow, 2002, and Adams-Guppy and Guppy, 2003). Another potential factor that may contribute to driver fatigue that has received little attention is WBV. Given the importance of identifying practicable efforts to mitigate driver fatigue in order to reduce accidents and injuries, a critical next step is to develop a more rigorous evidence base to examine possible causal links between WBV and fatigue. The development of such an evidence base would then lead to the next logical step, which would be to examine whether a device designed to reduce driver fatigue could have a measurable impact on truck-related crashes and fatalities.

This article summarizes the findings of a study conducted by the RAND Corporation that was commissioned jointly by AIG and Bose Corporation and had three primary aims: (1) to review and evaluate the literature on WBV and fatigue, (2) to provide modeling estimates of the association between WBV and fatigue and ultimately accident risk, and (3) to highlight future research directions in order to strengthen the evidence base concerning a causal role of WBV on fatigue and driver safety. A brief summary of findings pertinent to each aim is summarized herein.

The results of the literature review elucidated a number of important findings and limitations. Overall, the studies suggest that there is an association between exposure to WBV and increased fatigue or sleepiness; however, methodological limitations in the existing literature preclude definitive conclusions concerning the impact of WBV on driver fatigue/sleepiness. Out of 24 studies reviewed for this research, 18 show that exposure to WBV results in decrements in psychomotor performance or increases in sleepiness or fatigue. There were several important methodological limitations, however, that limit the generalizability of findings to real-world truck-driving conditions and that temper conclusions regarding a causal association between WBV and fatigue/sleepiness. In general, the reviewed literature is also limited by duration of WBV exposure; small participant samples that may not be representative of commercial truck drivers; and failure to consider other moderating influences that may potentiate the effects of WBV on fatigue, such as the presence of sleep disorders or pain. Furthermore, the reviewed studies primarily focused on performance metrics, rather than fatigue/sleepiness indicators specifically. Although these measures are clearly related, future research is needed that incorporates performance measures as well as subjective measures of fatigue/sleepiness and ideally objective measures of sleepiness as well, as these measures are ostensibly most closely linked with driver accidents.

Our efforts at modeling the relationship between WBV and fatigue-related vehicle crashes were somewhat limited, based on lack of existing data that connects WBV with crashes. Nevertheless, based on the available data and specific modeling assumptions (e.g., performance declines from fatigue induced by high acceleration WBV scale in time such as low acceleration WBV), model estimates suggest that the performance decrements associated with WBV exposure may be comparable to 22 hours of sleep restriction. In turn, prior work has shown that under sleep-deprived conditions, participants show performance decrements that are equivalent to being legally impaired, based on a blood-alcohol content exceeding the legal limit. Importantly, this latter observation is extremely tentative, given its reliance on several modeling assumptions and limited data to inform the models, and it merits additional study.

Finally, to address limitations in the existing literature, we also provide several suggestions for future research studies, including a laboratory design as well as a field-study design that could strengthen the evidence base. There are clearly advantages and disadvantages of both types of studies, including the trade-offs between generalizability of the findings (i.e., in a field study) versus experimental control to rule out confounding factors in a laboratory study. Pragmatic factors, including cost and duration of the study, are also crucial to consider.

In summary, although there was some inconsistency in the reviewed results and several methodological limitations in the existing literature, the results of this review and the preliminary (though suggestive) modeling estimates suggest that reducing WBV among commercial truck drivers is a modifiable target that may reduce fatigue and ultimately reduce the public-health burden and societal costs of trucking accidents. More methodologically rigorous examinations of the impact of WBV on fatigue/sleepiness, however, are needed to establish a causal relationship.