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Copyright
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(Copyright © 1995, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing) |
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Abstract
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An FHWA study was recently completed as part of its retroreflectivity research program; the goal was to determine minimum retroreflectivity requirements for traffic signs.
RESULTS were summarized in tables providing recommended minimum R sub a values for warning, regulatory, and guide signs, with the tables designed to provide a framework of minimum retroreflectivity requirements for field implementation. However, the level of accommodation could only be estimated in the range of 75 to 85%. The study measured luminance threshold for traffic signs. Subjects in a darkened laboratory viewed a series of scaled traffic signs. Simulated viewing distance was the "minimum required visibility distance", that is, the minimum distance that would allow a driver sufficient time to respond safely to the sign. Sign luminance was increased in steps until the subject was able to correctly recognize it. Data scatter plots showed an increased need for sign luminance with subject age. To specify the percent accommodated for the driving population, laboratory data were extrapolated statistically. For each sign, the mean and variance for the subjects tested were used to generate model data points, and percentiles were determined using U.S. driving population age distribution data. Analysis showed that 85% or more of all drivers (98 to 100% for most signs) would be accommodated by the level of retroreflectivity recommended for nearly all signs tested.
RESULTS indicate that minimum retroreflectivity table values are fairly conservative, allowing a margin for safety.
Record URL:
http://onlinepubs.trb.org/Onlinepubs/trr/1995/1495/1495-008.pdf
Language: en |