Citation

Elstad JO, Fitzpatrick JT, Woltman HL. Highw. Res. Board bull. 1962; 336: 51-60.

Copyright

(Copyright © 1962, National Research Council (U.S.A.), Highway Research Board)

DOI

unavailable

PMID

unavailable

Abstract

Signing on urban and rural roadways exhibits a complex of sign positions and ambient illumination levels suggesting need for determining optimum characteristics for retro- reflective materials under these conditions. Other studies have evaluated available reflective materials for individual effectiveness. This study is designed to establish reflective characteristics required for any installation and suggests a brightness range for typical sign environments. Ideally, consistent luminance would be maintained through approach distances for all sign positions. Iso-illuminance and iso-divergence data indicate varying illuminance and retro-reflective efficiency throughout the approach. However inverse relationship at generally useful distances indicates little modification of the classic divergence curve is necessary for materials considered. Ambient illumination of sign surfaces commonly ranges from 0.4 foot-candles in illuminated areas to less than 0.1 in rural locales. Current reflective materials provide good high beam performance and adequate low beam performance where ambient illumination incident on the sign surface does not exceed 0.4 foot- candles. In excess of 0.4 foot-candles, stream traffic provides additional useful luminance. Sufficiency values for sign luminance are presented for dark and illuminated locales.