Background: Bystanders can play a key role in preventing railway suicides by taking direct action or by raising an alarm. Aims: The study investigated in this context: (1) the prevalence of preventative actions by bystanders; (2) the relationship, if any, between first-hand preventions by bystanders and the degree of ambiguity around the imminence of danger; and (3) the nature of first-hand preventions by bystanders. Method: Data were obtained from a security reporting database at Sydney Trains for 2011-2019 for accident and suicide-related incidents (N = 1,278). Results: In 635 cases of suicide prevention, bystanders were identified as first responders in 11% of cases and as raising the alarm in 11% of cases. Bystanders as first responders intervened proportionally more where the ambiguity of danger is low (jumping) compared with high (sitting, standing, wandering). Of the 69 cases of bystander preventions, 77% involved physical interaction (e.g., holding back) and 49% involved more than one bystander. Limitations: The data source could be biased because of incompleteness or nonstandard reporting. Conclusion: Rail policy-makers should consider education and support for bystanders and staff: for example, by making known the prevalence of helping, the importance of intervening, and what types of intervention are most helpful.