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Any change to an operational system in the railway industry is met with rigorously engineered safety controls – whether it be a signalling system or a power distribution system, a strong emphasis is placed on engineering out risk: equipment should be designed and built with high resiliency, redundancy, availability, and so on. And yet even the most perfectly engineered signals, plant or rolling stock are still operated at some point by a human.

Humans are part of railway systems too, but humans cannot be engineered like a piece of physical infrastructure. Their propensity for “faults” (i.e., non-conformance behaviour) has to be built into the design, rather than built out of the design. Most safety-critical systems require human operators to make decisions based on the information on a computer screen, and yet the design of this Human-Machine Interface (HMI) is often overlooked in the rail industry as a significant risk factor. This is despite decades’ worth of examples from other industries that have implicated poor HMI design as a contributing factor in catastrophic failures of safety-critical systems.