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30 Pedestrian Detection Distance 7 The LEDs also had the shortest pedestrian detection distance due to the high effective intensity of the light 6 Attention-Getting Rating washing out the view of the pedestrian (Figure 17). 5 LED The other (non-LED) warning lights had similar per- Low Beacon Strobe formances to each other with regard to pedestrian detec- 4 High Beacon tion distance; however, the low-mounted beacons had the highest mean distance. This result may be because the 3 lights and the illuminated tailgate provided a contrasting background for the pedestrian's silhouette. 2 Confidence Rating The LEDs provided the highest confidence ratings due to 1 0 500 1000 1500 2000 2500 higher effective intensity; however, from an application Form Factor Method standpoint, the performance of every light was very high. The low-mounted beacons provided higher confidence Figure 18. Daytime attention-getting rating by the ratings than the high-mounted beacons of the same effec- light source effective intensity (17 scale). tive intensity. This result was because the high-mounted beacons were more affected by "daylighting" during the uphill conditions. The low-mounted beacons had a higher discomfort glare Attention-Getting Rating rating than the high-mounted beacons with the same The high effective intensity of the LEDs provided the effective intensity, probably because the light reflecting highest attention-getting ratings (Figure 18). off the tailgate added an additional source of glare. The low-mounted beacons provided higher attention- Urgency getting ratings than the high-mounted beacons (of the Higher effective intensity did not provide an additional same effective intensity) and the strobes (which had a urgency benefit. higher effective intensity). The added light reflection The rotating beacons and strobes yielded a higher rat- from the tailgate may have increased the low-mounted ing with a less intense light because the flash patterns beacons' visibility over the strobes. For the high-mounted appeared faster than the LEDs. beacons, low contrast as a result of being viewed against the sky is still a significant factor in the results. Discussion Discomfort Glare As expected, the LEDs (which have the highest effec- The experiment has shown that many of the factors in- tive intensity) resulted in the highest discomfort glare volved in the design and layout of a vehicle's warning-light ratings (Figure 19). system influence the response of the driver to that vehicle. 350 9 Pedestrian Detection Distance (ft) 300 Low Beacon 8 High Beacon Discomfort Glare Rating Strobe 250 7 6 200 LED 5 150 LED 4 Low Beacon Strobe 100 High Beacon 3 50 2 0 1 0 500 1000 1500 2000 2500 0 500 1000 1500 2000 2500 Form Factor Method Form Factor Method Figure 17. Pedestrian detection distance by the light Figure 19. Discomfort glare rating by the light source source effective intensity (Form Factor method). effective intensity (19 scale).

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31 The purpose of the dynamic experiment was to further re- Lighting Characteristics fine the requirements of the warning-light system in a driv- The effective intensity of the sources influenced the de- ing environment with the addition of adverse weather con- tection of the pedestrian and the assessment of the light ditions. The aspects of the warning-light system that must source glare. The higher effective intensity reduced the be considered are the lighting layout, adverse weather in- ability of the driver to see the pedestrian and also resulted fluences, further refinements of the lighting characteristics, in a higher discomfort glare rating. and influence of other environmental factors such as ap- The vehicle detection distance was reduced for the LEDs proaching vehicle glare. because of the system's longer flash duration. The double flash of the strobes and the effective intensity changes of Lighting System Layout the rotating beacon seem to have provided an additional Separation of the warning-light system from the tail clue to the nature of the lighting system. lights of the vehicle aided in the identification of the The urgency rating was also reduced for the LEDs. The vehicle. Many participants indicated that tail lights urgency of the lighting system also seems to be more were the important cue for the vehicle identification closely related to the apparent speed of the flashing. distance. Use of a double flash or a beacon seems to improve the One of the difficulties with placing the warning-light driver's response. system high on the vehicle is that the lights may appear against the sky. The lighting should be placed either such The use of a 360 light source close to the line of sight of that the vehicle is behind the source or such that a back- the driver increased the experienced glare; it should be ground is located behind the light in order to control avoided. the contrast. Other Environmental Factors Adverse Weather The presence of the opposing vehicle on the roadway re- The influence of the rain and fog conditions did not seem duced the pedestrian detection distance by increasing to significantly influence the participants' subjective the disability glare. ratings of lighting system performance. The opposing vehicle also reduced the discomfort glare The rain and fog significantly reduced the vehicle identi- ratings, because the warning-light systems are not as sig- fication and pedestrian detection distances for all the light nificant a source of glare as the opposing headlamps. sources and seemed to moderate the differences between The presence of the opposing vehicle did not affect the the systems except for the LEDs. vehicle identification distance. The LEDs resulted in much lower pedestrian detection The presence of other lighting systems, such as the road- distances than the other systems. The LED system had way lighting experienced during the surprise trial, greatly the highest effective intensity, which resulted in a larger reduced the discomfort glare rating of the warning-light amount of light scatter observed by the approaching systems but did not change the urgency rating. driver in rain and fog conditions. A higher effective-intensity light source may be required It is expected that the effective intensity of the light would in the presence of roadway lighting, or in daylight con- have to be limited to avoid the impact of light scatter ditions, as suggested by the lane-change distance results under adverse weather. from the surprise trial.