Abstract
Road traffic injuries are among the leading causes of adolescent death worldwide. Within New Zealand, young drivers are disproportionately represented in crash statistics, contributing to a large portion of fatalities, while also engaging in higher rates of risky driving behaviours than older drivers. On-road risk taking among young drivers may be exacerbated by the poor sleep that this demographic experiences, and despite existing research suggesting that risk perception may influence this sleep-driving relationship, risk perception has not been explored as a mediating variable. The current thesis investigated the role of risk perception in the sleep-driving relationship among young New Zealand drivers, hypothesising that risk perception would function as a partial mediator. Seventy-seven young New Zealand drivers aged 16-20 years, who held at least a restricted license, completed a one-week observational study involving naturalistic sleep tracking using actigraphy and daily sleep diaries. Objective and subjective sleep duration, and self-reported sleep quality, were measured in the 24 hours prior to testing and averaged across one week. Participants completed video-based risk perception tasks, and a simulated drive – which measured objective speeding, tailgating, and brake and accelerator behaviours. Hayes mediation analyses found no evidence that risk perception mediated the relationship between sleep and risky driving at the level of a medium effect size; therefore, the main hypothesis was unsupported. However, lower perceived risk for speed and following distance consistently predicted greater levels of risky driving, across all models. This suggests that low risk perception among young New Zealand drivers may contribute to risky driving independent of sleep. It follows that risk perception could provide an avenue for future research and interventions aiming to reduce risky driving and crash rates among young New Zealand drivers.
An investigation of community perceptions of sleep and fatigued driving was embedded in the current study, as a replication of Paterson et al. (2016). Two outcomes were hypothesised: 1) less sleep in the prior 48 hours would be associated with the perception that fewer hours of sleep are required to drive safely, and; 2) that the young New Zealand drivers would report that less hours of sleep were needed to drive safely than the older Australian sample used in the original paper. Participants completed a questionnaire assessing sleep history in the past 48 hours, perceived sleep required to drive safely, tired driving, and falling asleep at the wheel. Cumulative Link Models showed that prior sleep did not predict perceptions of the minimum sleep required for safe driving, although the current study was underpowered to adequately detect the small effect sizes previously reported. Consistent with the second hypothesis, young New Zealand drivers reported that five to seven hours of sleep were sufficient to drive safely, representing a one-hour downward shift compared with the older Australian sample from the original study. A large portion of young New Zealand drivers also reported frequently operating a vehicle when too tired to drive safely. Together, these findings suggest that young New Zealand drivers underestimate the amount of sleep required to drive safely, and highlight the need for interventions which educate this population on the consequences of fatigued driving and crash risk.