How are drivers’ stress levels and emotions associated with the driving context? A naturalistic study

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IntroductionUnderstanding and mitigating drivers' negative emotions, and stress levels, is of high importance for enhancing road safety, and human well-being. While detecting drivers' stress and negative emotions can significantly help with this goal, understanding what might be associated with increases in drivers' negative emotions and high stress level, might better help with planning interventions, which has not been explored in detail. Methods: In this study, by using a naturalistic driving study database, we analyze the changes in drivers' heart rate and facial expressions with respect to the changes in the driving scene, including road objects and the dynamical relationship between the ego vehicle and the lead vehicle. Results: Our results indicate that different road objects might be associated with varying levels of increase in drivers' HR as well as different proportions of negative facial emotions detected through computer vision. Larger vehicles on the road, such as trucks and buses, are associated with the highest amount of increase in drivers' HR as well as negative emotions. Additionally, shorter distances and higher standard deviation in the distance to the lead vehicle are associated with a higher number of abrupt increases in drivers’ HR, depicting a possible increase in stress level. Our finding indicates more positive emotions, lower facial engagement, and a lower abrupt increase in HR in highway environments. Conclusion: This research collectively shows that certain road environments such as highways with less stress-inducing objects are much more suited to promote drivers well-being and should be considered in routing use cases.