Solid-State Roadway Lighting Design Guide: Volume 2: Research Overview (2020) / Chapter Skim
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38 According to the project plan, the tasks to be completed as part of this project included the execution of the research work plan (Smart Road testing) , development of the SSL Guide, and inclusion of a research and implementation roadmap of recommended future research and the approximate associated costs.
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Research and Testing Results 39 Experimental Design A repeated-measures experimental design was used to assess the effects of light SPD, light level, surround ratio, and uniformity ratio on driver visual performance. Driver visual performance was measured according to the distance at which participants detected objects as they drove through the test environment.
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40 Solid-State Roadway Lighting Design Surround Ratio. The surround ratio is the measure of how bright the roadway travel lanes are with respect to the adjacent areas of paved and unpaved shoulder.
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Research and Testing Results 41 that may be on or near the roadway and are just large enough that they may cause damage to a vehicle, and pedestrians were used because they are commonly encountered in many driving scenarios and can also represent the presence of wildlife. Each of these objects was presented in a different color and at a different offset distance from the roadway to simulate hazards on the roadways.
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42 Solid-State Roadway Lighting Design Light Type Pedestrian Offset Target Offset 2 ft Right 10 ft Right 2 ft Right 2 ft Left High Light Level 2100K HPS 19.9 14.9 17.5 21.1 3000K LED 21.5 15.1 18.5 21.9 4000K LED 20.1 15.9 17.8 22.7 5000K LED 22.3 16.7 18.3 22.5 Medium Light Level 2100K HPS 13.8 9.7 11.1 13.5 3000K LED 14.7 10.6 11.8 14.2 4000K LED 14.3 9.2 12.4 13.6 5000K LED 13.7 10.2 11.4 14.4 Low Light Level 2100K HPS 8.9 5.8 7.1 8.9 3000K LED 9.4 6.5 6.9 9.1 4000K LED 9.1 5.9 7.6 9.6 5000K LED 8.5 6.3 7.4 9.7 Note: HUR = high uniformity ratio; HSR = high surround ratio. Table 5.
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Research and Testing Results 43 includes 75 poles that each support three luminaires (Figure 18)
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44 Solid-State Roadway Lighting Design Figure 19. Custom shields: (a)
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Research and Testing Results 45 Pedestrians The pedestrians were on-road experimenters wearing colored surgical scrubs (Figure 22) , which allowed the pedestrian to have a consistent color contrast.
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46 Solid-State Roadway Lighting Design travel with two illuminance meters mounted at 5 ft (∼1.5 m) high and at the quarter-lane position.
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Research and Testing Results 47 Light Type Shield Light Level Uniformity Ratio (Average/Minimum Illuminance) 2100K HPS HSR-HUR Medium 7.5 5000K LED High 7.5 4000K LED 3.8 3000K LED 3.8 5000K LED Low 4.9 4000K LED 3.7 3000K LED 5.8 5000K LED Medium 6.1 4000K LED 4.6 3000K LED 6.8 4000K LED HUR-LSR High 4.1 Low 7.2 Medium 5.1 LUR-HSR High 6.7 Low 4.3 Medium 4.6 LUR-LSR High 3.5 Low 4.5 Medium 3.6 Table 9.
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48 Solid-State Roadway Lighting Design As participants drove through the laps, several objects were presented at designated stations. Participants were asked to verbally identify the type of object (pedestrian or target)
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Research and Testing Results 49 Detection Distance Analysis. In the first analysis, a linear mixed model (LMM)
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50 Solid-State Roadway Lighting Design Perception of Discomfort Glare Across LED and HPS Light Sources The goal of this analysis was to determine whether differences in the perception of discomfort glare occurred between LED light sources of different CCTs, a legacy HPS light source, and unlighted conditions. One LMM was used to assess the effects of the type of light source on the perception of discomfort glare.
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Research and Testing Results 51 pedestrians, polygons were traced around the pedestrian (Figure 25) and target, and the software calculated the mean luminance within the selected polygon.
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52 Solid-State Roadway Lighting Design Degrees of Freedom Source Numerator Denominator F-Value p-Value Age 1 33.3 30.2 <.0001 Surround ratio 1 34.2 18.8 0.000 Light level 2 2,082.5 26.2 <.0001 Speed 1 2,114.1 71.1 <.0001 Clothing color 3 2,082.2 61.7 <.0001 Offset 1 2,082.2 369.0 <.0001 Age surround ratio 1 34.3 5.8 0.022 Age speed 1 2,117.1 15.1 0.000 Age offset 1 2,082.2 29.9 <.0001 Surround ratio light level 2 2,082.5 4.2 0.015 Surround ratio clothing color 3 2,082.2 6.5 0.000 Type of light source speed 2 2,106.5 12.6 <.0001 Light level clothing color 6 2,082.2 14.8 <.0001 Speed clothing color 3 2,082.2 12.2 <.0001 Speed offset 1 2,082.2 15.7 <.0001 Clothing color offset 3 2,082.2 29.6 <.0001 Age surround ratio light level 2 2,082.5 6.8 0.001 Age surround ratio speed 1 2,117.9 15.7 <.0001 Age speed * clothing color 3 2,082.2 2.9 0.034 Uniformity ratio surround ratio speed 1 2,114.5 10.5 0.001 Surround ratio type of light source speed 2 2,106.8 3.6 0.028 Surround ratio type of light source offset 2 2,082.3 3.5 0.030 Surround ratio light level clothing color 6 2,082.2 9.1 <.0001 Surround ratio light level offset 2 2,082.3 9.7 <.0001 Surround ratio speed clothing color 3 2,082.2 8.7 <.0001 Light level speed offset 2 2,082.3 10.1 <.0001 Light level clothing color offset 6 2,082.3 14.9 <.0001 Speed clothing color offset 3 2,082.3 15.4 <.0001 Uniformity ratio surround ratio type of light source speed 2 2,106.6 3.2 0.041 Uniformity ratio surround ratio type of light source clothing color *
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Research and Testing Results 53 Interactive Effect of Type of Light Source, Surround Ratio, and Offset. The combined effects of type of light source, surround ratio, and offset on detection distance are summarized in this section.
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54 Solid-State Roadway Lighting Design Pedestrian at 2 ft Right Distance (ft) Distance (ft)
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Research and Testing Results 55 the 10-ft offset location were not as high as the differences at the 2-ft location, perhaps because the pedestrian at the 10-ft offset location was rendered in negative contrast under both surround ratio conditions (Figure 29)
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56 Solid-State Roadway Lighting Design Interactive Effect of Light Level, Surround Ratio, and Clothing Color. The combined effects of light level, surround ratio, and clothing color on detection distance are summarized in this section.
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Research and Testing Results 57 contrast when the negative contrast transitions to positive contrast) occurred (Figure 34)
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58 Solid-State Roadway Lighting Design contrast (more negative contrast) to be detected, as they were offset from the line of sight of the driver.
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Research and Testing Results 59 the high surround ratio than under the low surround ratio (Figure 36)
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60 Solid-State Roadway Lighting Design detecting a pedestrian. Higher surround ratios and higher uniformity ratios also increase the odds of detecting the pedestrian safely by 2.6 and 2.3 times, respectively.
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Research and Testing Results 61 * Degrees of Freedom Source Numerator Denominator F-Value p-Value Age 1 33 34.6 Light level 2 1,368.1 46.2 Speed 1 1,395 26.6 Target color 2 1,367.5 13.5 Offset 1 1,368.1 19.0 Age light level 2 1,367.9 5.9 Age target color 2 1,367.5 4.7 Age offset 1 1,367.7 7.2 Uniformity ratio target color 2 1,367.2 10.0 Uniformity ratio offset 1 1,367.9 16.4 Surround ratio target color 2 1,367.4 10.4 Type of light source light level 4 1,367.9 2.5 Type of light source speed 2 1,385.3 11.5 Light level speed 2 1,367.6 16.2 Light level target color 4 1,367.4 29.9 Light level offset 2 1,367.5 7.4 Clothing color offset 2 1,367.2 12.3 Age uniformity ratio target color 2 1,367.2 3.2 Age uniformity ratio offset 1 1,367.5 13.2 Age type of light source speed 2 1,397.8 3.7 Age speed target color 2 1,367.3 3.5 Uniformity ratio surround ratio offset 1 1,367.1 7.3 Uniformity ratio type of light source light level 4 1,367.6 3.0 Uniformity ratio type of light source target color 4 1,367.1 2.5 Uniformity ratio type of light source offset 2 1,367.3 4.5 Uniformity ratio target color 2 1,366.9 5.3 Surround ratio type of light source light level 4 1,367.5 2.7 Type of light source target color offset 4 1,367 3.7 Light level speed target color 4 1,367.6 35.6 Light level speed offset 2 1,367.3 4.6 Light level target color offset 4 1,367.3 20.1 Speed target color *
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62 Solid-State Roadway Lighting Design different. An increase in light levels across all types of light sources and uniformity ratios resulted in longer detection distances (Figure 38)
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Research and Testing Results 63 LED 3000K LED 4000K LED 5000K LED 3000K LED 4000K LED 5000K Note: Values are means of detection distances and error bars represent standard errors. Figure 39.
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64 Solid-State Roadway Lighting Design blue-colored targets were longer than those for gray- and red-colored targets (Figure 43)
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Research and Testing Results 65 0 50 100 150 200 250 300 Blue Gray Red D et ec tio n D is ta nc e (f t) Target Color LED 3000K LED 4000K LED 5000K Note: Values are means of detection distances and error bars represent standard error.
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66 Solid-State Roadway Lighting Design in higher negative contrast could have resulted in a longer detection distance than that of the gray target, which was rendered in positive contrast. Further, the contrast of the blue target was higher in magnitude than that of the red target (Figure 45)
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Research and Testing Results 67 The odds ratio estimates of each of the significant factors and the 95% confidence intervals are shown in Table 16. As with the pedestrian detection task, the odds of detecting the targets from a safe distance were 1.6 times higher under the high light level as compared with the medium and low light levels.
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68 Solid-State Roadway Lighting Design Independent Variable Level Reference Level Odds Ratio 95% Confidence Limits Light level High Medium 1.6 1.1–2.3 High Low 1.6 1.1–2.3 Age Younger Older 3.8 2.1–6.8 Offset 2 ft left 2 ft right 1.4 1.0–1.9 Speed 35 mph 55 mph 20.2 12.5–32.8 Table 16. Odds ratios of significant factors in MMLR analysis of detection of pedestrians.
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Research and Testing Results 69 Pedestrian Detection Task -- Safe Stop Analysis. All significant MMLR results are summarized in Table 18.
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70 Solid-State Roadway Lighting Design Of all the light sources, 3000K LED had the lowest detection distance, and the differences between 3000K and 4000K LED were statistically significant (Figure 49)
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Research and Testing Results 71 between high and low light levels, the high light level having a higher glare rating than the low light level (Figure 50)
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72 Solid-State Roadway Lighting Design to detect the pedestrians or targets from a safe distance. The only statistically significant differences in the visual performance of pedestrian and target detection were those between the lighted and unlighted conditions.
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Research and Testing Results 73 Effect of Surround Ratio Surround ratios significantly affected driver visual performance. Increases in the surround ratio increased visual performance, as evidenced by longer detection distances and increased odds of detection from a safe distance.
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74 Solid-State Roadway Lighting Design lowest odds of being detected from a safe distance. These results also indicate that pedestrians should refrain from wearing black-colored clothing in nighttime roadway environments to increase their visibility.
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Research and Testing Results 75 Research Roadmap The following areas of research should be considered to better understand the impacts and benefits of SSL. Areas of funding include NCHRP and FHWA.
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76 Solid-State Roadway Lighting Design integrated asset management program and can serve as a starting point for exploring real-time management of lighting systems within the ITS framework. Future research will be needed to address integration with Smart city systems and connected and autonomous vehicle systems.
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