The Development Of A Visibility Tool To Support Sign And Signalling Work On The Railway

With sponsorship from Network Rail, Human Engineering Limited and the University of Bristol conducted a programme of work which aimed to assess the feasibility of, and subsequently develop, a visibility assessment tool to support Network Rail's sign and signal sighting work on the railway. This paper outlines the development of this visibility tool, the 'conspicuity camera', from its conception to the current time.In the first phase of this program, the distances at which a range of signs could be detected were determined through trials in a virtual simulator, at a range of linespeeds. From this, an angular subtense could be calculated for each sign; the smaller the angular subtense, the greater the visibility of the sign.In the second phase of the study, the application potential of using angular subtense to inform on visibility was explored. Specifically, this phase began to examine the feasibility of developing a tool, composed of a digital SLR camera and the "Cortex Model" of primate vision, in the prediction of railway signal/sign visibility. Signs from a virtual reality environment were photographed at a range of angular subtenses, and these were subsequently analysed in the related Cortex Model. Output from this phase demonstrated that the Cortex Model was able to predict the detection of signs in realistic settings. The most recent phase of work defined a baseline set of visibility measurements, i.e. a range of conspicuity thresholds, from the Cortex Model from signs and signals in the real environment, and validated the model output against subjective estimates from Subject Matter Experts (SMEs).It is envisaged that Network Rail could deploy the conspicuity camera in future to ensure that the signals and signs along a route are clearly visible to drivers.