S&TEngineer wrote:The overall mode of operation is no different to any other UWC. No signal interlocking is provided for the gates, only for the Miniature Red/Green lights.
Yes, I understood that conceptually having a motor open the gates is no different to the user opening the gates by hand, and was intended to avoid having the gates left open.
But can you not see that there is an important psychological difference to the road user?
In the traditional UWC the user has to manually open the gates. It is very clear to them that opening the gates says nothing about whether a train is approaching.
With POGO, the system itself opens the gate after a request from the user. Many users would take this as authorisation to cross; after all this is the common experience of gates and doors. You ask for permission to enter, the gate or door is opened to allow you to enter (or it remains closed to deny you permission). Indeed, countering another instance of this experience/expectation is exactly what POGO was intended to address: users coming to the crossing, finding the gates open, and assuming this means they can cross without any further check.
Yes, there are lights, and signs explaining the expected behaviour. It's well known in user interface design that instructions are the very worst way of conveying information to users. Some users won't take the instructions in, or will misinterpret the instructions. Some users will attempt to follow the instructions, but get confused when the behaviour of the crossing conflicts with their expectations (I checked the green light is showing, I pushed the button to open the gate, the gate is now open but the light is red. Does this mean it's safe or not safe?)
In fact, the conflict with users' experience of gates and doors is so strong that I would expect that even users that have been instructed what to do could get trapped if they are tired or distracted.
I'll re-iterate: I think this is a stupid, dangerous, design. I think it came about because the designers focused on one aspect of the problem (gates being left open) and failed to think about how the users would experience the resulting interface. The designers' blind spots are even clearer when you consider the report's comments about the lack of any risk analysis during design, or even pilot use. It becomes glaringly obvious when you consider that the risk was clearly identified twice, and at least once dismissed as 'cosmetic'. Certainly nothing was done to address the risk.