Guidelines for Nighttime Visibility of Overhead Signs (2016) / Chapter Skim
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16 Closed-Course Study As discussed in Chapter 2, recent trends indicate a movement away from lighting overhead guide signs toward relying on retro reflective sheeting and vehicle headlamps assumed to provide nighttime drivers with sufficient sign luminance for visibility. There are various guidelines suggesting how much illuminance or luminance should be provided, and the MUTCD provides minimum maintenance standards for retroreflectivity when sign lighting is not used.
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17 lighting. The two systems consisted of HPS and LED lights.
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18 Figure 5. Measures of illuminance and luminance (at 300 ft with Type XI green sheeting)
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19 The legends have mixed-case letters with a size corresponding to an uppercase letter height of 16 in. The typeface was Clearview 5WR font.
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20 Participants were assigned a secondary task in which they were asked to read aloud the speeds posted on a speed limit sign. The speeds shown were either 35 or 55 mph.
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21 rectangles covered four regions on the legend and four on the background. A Weber contrast value for each image was calculated from the average luminance of the legend and background, according to Equation 1: = − (Eq.1)
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22 Figure 11. Distribution of legend luminance measured at 640 ft under the closed-course factorial conditions.
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23 distance from one observation to another was analyzed with respect to the categorical variables from the factorial experiment (sign lighting type, lighting intensity level, use of overhead street lighting, and sign sheeting material) and the values of luminance and contrast at 640 ft that resulted from the experiment design.
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24 on either of the two measurements. Additionally, statistical analysis indicated that there was no relationship, even when considering a potential interaction.
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25 and standard deviations are shown in Figure 17. Based on visual inspection of each condition group in Figure 17, legibility distances were consistently longer for younger drivers and when roadway lighting was on.
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26 0 10 20 30 40 50 500 600 700 800 900 1,000 100% 50% 25% 100% 50% 25% 0% HPS LED NONE Lu m in an ce (c d/m 2 ) Le gi bi lity D ist an ce (ft )
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