Commuting to work by car is a frequently occurring activity that poses a salient risk to worker safety. Although general stress perceptions have been linked to indicators of unsafe commuting in cross-sectional studies, little is known about whether and how day-to-day variability in stressor exposure and subjective and affective strain reactions covary with intraindividual variability in unsafe driving while commuting over time. A major contributor to this knowledge gap is the lack of a validated methodology to link subjective self-report variables to objective driving performance criteria in a naturalistic commuting environment. Data were collected from university staff employees (N = 50) over a 2-week sample of daily experiences and objective recordings of unsafe driving behaviors. We applied a multilevel methodology to evaluate a model in which exposure to daily hindering and challenging components of work stress, end-of-workday psychological distress, and end-of-workday negative affect influence objectively monitored unsafe driving behaviors in a naturalistic commuting environment. Results indicated that employees were less likely to drive unsafely during their postwork commute on days in which they encountered more challenge stressors at work (odds ratio = .63). However, employees who experienced heightened negative affective spillover were more likely to drive unsafely during their postwork commute (odds ratio = 1.96). We discuss the theoretical, practical, and methodological implications of our findings for research on employee commuting safety. (PsycINFO Database Record (c) 2019 APA, all rights reserved).