RAILWAY AGE, MARCH 2021 ISSUE (expanded version): Exploring train control system Human Machine Interface requirements. Requirements for safety-relevant Human Machine Interfaces (HMIs) for train operators are becoming more common around the world. The evolution toward safety-relevant HMIs for train control is already well under way in Europe and Asia, most notably as part of the widespread adoption of the European Train Control System (ETCS), with more than 50,000 miles of the worldwide rail network equipped or contracted to be equipped with ETCS (8). While HMI safety requirements have not yet become widespread in North American rail applications, the anticipated re-emergence of HMI safety requirements could soon be an example of history repeating itself.