Abstract
A system of computer-controlled variable message signs (matrix signs), which was implemented several years ago on many sections of Dutch freeways, is described. The signs can display messages like speed limits and 'change lane'. The main conclusions from an evaluation study are that the system reduces the number of accidents considerably, but has less influence on traffic flow. Field trials to determine optimum display features are described. These trials provided relations between the most relevant photometric quantities: horizon luminance, message luminance, pixel intensity and inter-pixel distance. Practical examples of the control of the sign's light output as a function of varying ambient light level are given.
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