Variable-message signs (VMS) are used for a number of applications. Whatever the application, road users must be able to see, read, and understand these signs. An experiment using observers and singleletters of the alphabet, determined contrast and luminance criteria that are now incorporated as requirements in French specifications. They apply to all types of pattern and to all of these technologies. A specific measuring method for day and night visibility, based on luminance contrast for day and character luminance for night visibility, has been developed in the photometric laboratory. "Intelligibility" is the third property used to qualify a sign. It concerns the last stage in the perception of a signal. Here understanding the sign depends on recognizing the usual symbol. A laboratory study of the understanding of six types of matrix sign pictograms was conducted using transparencies produced by the EDGAR graphic software developed for the purpose. The signs were presented to observers for a limited time. The influences of the number of points in the matrix and ofthe shape of the symbol were investigated. This study raises the problem of specifying matrix symbols. It should be continued in an attempt to arrive at simple recommendations for the main symbols.
Abstract