This report summarises the on-road research trials, which were conducted to investigate the effect of dew formation on retro-reflective sign face materials. This included an assessment of the loss of conspicuity and legibility with the presence of dew on the sign face. A luminance camera was used to obtain objective luminance measurements of a series of traffic signs. Digital images were also taken and used as part of a subjective paired comparison of sign faces, with and without the presence of dew. The results of this work showed a mean reduction in sign luminance values and a reduction in contrast ratios with the presence of dew on a sign face. The results of this research provided recommendations on the use of dew resistant overlay films on traffic signs, sign mounting methods and sign maintenance.

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