HOF in SPADs

Introduction

Signals passed at danger (SPADs) are one of the highest profile risks in railway operations, and the immediate cause of SPADs is often an action or inaction by the individuals involved, usually the train driver but potentially also signallers or maintainers. However, the focus on these errors often disguises the fact that the vast majority of trains (and train drivers) do stop at red signals when they encounter them, and that there are always underlying systems factors influencing the rare errors. Looking beyond the error and understanding the underlying factors that contribute to the rare occasions when SPADs happen can help to reduce the risk by identifying mitigations for, or ideally designing out, those factors.

Relevance to rail

Some, though by no means all, of the factors which have been found to contribute to SPADs include:

• Cab layout – poor layouts of cab controls or visibility from cabs can increase SPAD risk
• Time pressure – late running can increase pressure to depart and reduce attention to signals
• Distractions or incorrect cues given at stations – distractions dealing with passengers, or incorrect departure cues from station staff can increase SPAD risk
• Poor sighting of signals – reduced time to see and react to signals reduces the opportunity for drivers to detect and correct their errors
• Congested networks – higher numbers of trains in an area increases the probability of encountering restrictive signal aspects and reduces drivers’ expectation of a stop signal reliability following a caution signal.