Guidelines for Nighttime Visibility of Overhead Signs (2016) / Chapter Skim
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Pages 5-15
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From page 5... ...
5 Background Traffic control devices (TCDs) must be visible at an appro priate distance for drivers to respond to them properly.
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6The 2.3 cd/m2 luminance value that met the needs of 50 per cent of older drivers at a 40ft/in. index was adequate for approximately 80 percent of the drivers at a 30ft/in.
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7 reflective and the backgrounds that are not independently illuminated should be retroreflective. Additionally, it states that the illumination provided by lowbeam headlamps is relatively small.
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8Table 3 shows the recommended IESNA lighting levels, based on the same three ambient lighting classifications. Based on the MUTCD guidelines and those in Tables 2 and 3, there appears to be a general consensus that sign light ing is not needed in rural areas as long as the retroreflective sheeting meets the MUTCD minimum standards.
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9 interest among transportation agencies to determine when sign lighting is appropriate. As retroreflective sign sheeting materials have become more efficient in terms of returning headlamp illumination back to the driver, there has been a trend to turn off or remove most overhead guide sign lighting.
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10 and Florida with a policy for lit street name signs when pos sible. The other agencies do not have internally illuminated street name signs within their jurisdiction, though there is no prohibition against local municipalities lighting street name signs as long as they are responsible for the costs and maintenance.
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11 and appearance of various combinations of sign sheeting types used on legends and backgrounds (24)
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12 heat that did not have as great of an effect on sealed beam headlamps (30) .The evolution of headlamps has resulted in less illumination reaching traffic signs, whether a result of changes in the distribution of light or the construction that allows for degradation from the natural elements.
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13 Measurements presented by Adrian and Bhanji showed that much of the scattering also occurs in the vitreous humor (52)
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14 on the expected message of the sign. In some circumstances, however, unfamiliar drivers may read a sign without having initial clues regarding its message.
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15 sheeting type) that influence visibility, whether measured as recognition or legibility.
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