Common mental disorders (CMD) contribute to overall burden of disease. The current study aimed to describe the prevalence of CMD among a sample of bus drivers and fare collectors in Greater Metropolitan Belo Horizonte, Minas Gerais State, Brazil, and investigate whether traffic conditions and conditions inside buses were associated with the outcome. This non-probabilistic sample of 1,607 workers was estimated from the size of the effective workforce (n = 17,470). Face-to-face interviews used a digital questionnaire with online data processing. Overall prevalence of CMD was 23.6%. Bad traffic conditions lost statistical significance in the multivariate analysis, while higher income and adverse working conditions and inadequate safety remained associated with the outcome. Harmful behavior and vulnerable health situations were associated with CMD. This study of urban bus workers' health is a unique contribution that can provide backing for public policies targeting metropolitan populations.