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Citation |
Griffith MS, Paniati JF, Hanley RC. Transp. Res. Rec. 1993; 1421: 53-60. |
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Copyright |
(Copyright © 1993, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing) |
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DOI |
unavailable |
PMID |
unavailable |
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Abstract |
The primary objective of this study was to examine the validity of the maximum specification (30 degrees) for entrance angles of retroreflective traffic signs, which is considered to be the widest angle for signs. However, the 45-year-old specification is not substantiated by empirical data. Accurate data are necessary to evaluate the need for a new specification. The amount of light returned from a sign to a driver determines retroreflectivity; therefore, research was conducted from the driver's perspective. Measurements of sign entrance angles were made and their distribution was analyzed. A customized computer software program, SEAMS (Sign Entrance Angle Measurement System), was used to measure entrance angles for over 1,100 in-service traffic signs on several roadway types. After examination of previous research and consideration of other factors, it was decided to take sign entrance angle measurements at 30.5 and 61.0 m (100 and 200 ft). Using the 61.0-m (200-ft) distance for freeways and the 30.5-m (100-ft) distance for nonfreeways provided a conservative estimate of sign entrance angles. The empirical distributions show that approximately 95% of the sign entrance angles measured are less than 21 degrees and approximately 99% are less than 27 degrees. The study results indicate that the current 30-degree specification covers nearly all signs and provides a margin of safety to compensate for signs that are twisted, bent, or leaning out of plumb. However, the data also show that a lower specification (20 degrees) would cover 99% of the freeway signs and 96% of all signs measured. Language: en |