The objective of this paper is to derive a preliminary traffic signal standard for round signals based on the extensive, worldwide scientific research addressing the visibility and conspicuity requirements of traffic signals. The literature was reviewed, analyzed, summarized, and critiqued by a group of experts in visibility and related sciences, and a preliminary standard was derived from these analyses. The preliminary standard includes specifications for color, peak daytime intensity, intensity distribution, nighttime intensity anddimming, use of backplates, effects of depreciation and phantom limits for both 8-in. (200-Mm) and 12-in. (300-Mm) red, green, and yellow signals. This paper appears in transportation research record no.1316, Visibility for roadways, airways, and seaways 1991: proceedings of a conference, july 25-26, 1990, washington, d.C.
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