Fatigue, as a persistent and serious occupational hazard, plays an important role in traffic accidents by reducing the driver's ability to maneuver with the vehicle and increasing the likelihood of falling asleep at the wheel. The purpose of this study was to identify the individual contextual factors, sleep condition, lifestyle, job characteristics, environmental, and economic conditions that affect the fatigue and alertness of Iranian suburban bus drivers. A questionnaire-based cross-sectional survey was used for this study. Non-probability sampling was used to study 401 suburban bus drivers from Tehran province, Iran, ranging in age from 24 to 67 years. The SPSS22 statistical software V27 was used for the analysis. Approximately half of the participants (50.5%) had experienced fatigue while driving in the previous six months. According to a logistic regression analysis, the contextual factors were all independently related to falling asleep and fatigue while driving. This study provides a thorough understanding of the contextual factors related to drowsy driving and emphasizes the importance of taking these things into consideration when developing interventions aimed at improving the driver's wellbeing and health and lowering the risk of errors and accidents.