Nighttime Expert Panel and Photometric Evaluations of Unlighted Overhead Guide Signs

Abstract

A nighttime field evaluation of four different retroreflective overhead-sign sheeting combinations (ASTM D4956 beaded Type III legend on beaded Type III background, Type IX legend on beaded Type III background, Type IX legend on Type IX background, and Type VII legend on beaded Type III background) was conducted on a section of US-30 near Mansfield, Ohio. The test-material combinations were compared when lighted and unlighted (illuminated by low-beam headlights only). Twelve Ohio Department of Transportation engineers and technicians served as evaluators, riding the test loops in 2002 Dodge Caravans. The white Type IX legend on green-beaded Type III background sheeting combination received the highest evaluation scores for appearance, conspicuity, and legibility. The scores for the Type VII legend on beaded Type III background signs were only slightly lower in all three categories. The Type IX legend on Type IX background combination received slightly lower evaluation scores, and the beaded Type III legend on beaded Type III background combination received the lowest evaluation scores. The same signing material combinations were also photometrically (luminance and luminance contrast ratio) evaluated under low-beam illumination at selected approach distances from 200 to 1,000 ft (61 to 305 m) using a 1984 Peterbilt truck, a 2002 Chrysler Town and Country minivan, and a 2002 Toyota Camry sedan, both when lighted and unlighted (low beams). Unlighted overhead signs made with either the white Type VII or the Type IX legends on green-beaded Type III backgrounds provide nighttime motorists with adequate appearance, conspicuity, and legibility.

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