On the third of April there was a low-speed collision between two passenger trains at Plymouth station. A local train from Cornwall ran into the back of a stationary London-bound express. Though nobody was killed, thirty-five people were injured, a couple of them seriously.
The preliminary report makes it sound like an archetypal “Swiss cheese” incident.
If you imagine safety represented by several layered slices of Emmental cheese; each hole in the cheese represent an opportunity for human error to creep in, but an accident can only get through when all the holes line up. The more layers of safety the better.
This was what seems to have happened at Plymouth.
The normal pattern of operation was disrupted due to scheduled maintenance on the lifts, causing trains to be diverted away from their regular platforms. The signaller wrongly estimated the amount of space in the platform behind the express, and thought the local train would fit in behind it. The driver of the local train wasn’t expecting the platform to be part-occupied by another train. And because the approach at the western end of the station is on a very sharp curve, the driver didn’t realise the express was on the same track until it was too late to stop.