This paper describes a skill decay prediction model that was applied to a safety critical task conducted by rail workers. The tool is easy to use and promotes skill maintenance for operators in environments that have an increased risk of skill decay. A skill decay analysis tool called the User Decision Aid was adapted for use in a large, transportation organisation. The tool is an easy-to-use method that has proven useful in guiding training to prevent the degradation of skill and knowledge in various tasks. It produces skill decay curves, addressing questions such as how frequently should an operator receive training or undertake practice in an activity, to remain skilled and competent in that activity? The skill decay tool provides useful benefits to organisations as it allows the judicious allocation of training resourcing, and can guide the design of tasks.