Sign luminance requirements for various background complexities
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Sign luminance requirements for various background complexities

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    The Federal standards (FP-79) for luminance of retroreflective materials for traffic signs are acceptance standards; they provide no differentiation based on driver need. Driver needs for sign luminance are of 3 types -- luminance for sign comprehension, luminance levels that define sign legibility, and luminance levels for sign conspicuity. This study was directed toward establishing, for different levels of scene complexity, luminance levels for conspicuity of yellow diamond warning signs at night. A procedure based upon rating sign locations on 4 scales was useful for identifying low complexity and high complexity scenes. A field study demonstrated that at low complexity sites, Type I I signs degraded to 36 percent of Federal standard provided adequate luminance (.14 candelas/ft2) (1.51 candelas/m2) for sign recognition beyond 500 ft (150 m). At high complexity sites, new Type II signs in excess of the federal standard of provided luminance (.40 candelas/ft ) (4.3 candelas/ m ) that was inadequate for sign recognition at 500 feet (150 m). At speeds below 35 mi/h, the required recognition distance is less and signs degraded to 72 percent providing a luminance of .25 candelas/ft2 (2.69 candelas/m2) were adequate. The results clearly support earlier research in demonstrating that the visual complexity of a scene is a very important factor in determining nighttime sign luminance requirements.
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