Human Factors Guidelines for Road Systems: Second Edition (2012) / Chapter Skim
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Pages 206-218
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Countermeasures for Mitigating Headlamp Glare .
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COUNTERMEASURES FOR MITIGATING HEADLAMP GLARE Introduction Countermeasures for mitigating headlamp glare refers to road design elements that are effective for reducing the discomforting and disabling effects on visibility of exposure to glare from oncoming headlamps. The combination of high-intensity headlamps and high mounting heights in the vehicle fleet can result in greater exposure to glare for motorists.
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Di scu ssi on Glare occurs when the intensity of a light source within the visual field is substantially greater than the visual adaptation level, causing physical discomfort or pain (dis comfort glare) and/or reduced visibility (disability glare)
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N IG HT TI ME D RI VI NG In tr od uc ti on Nighttime driving refers to particular challenges to motorists' visibility while driving in darkness on rural roads. The farthest distance at which drivers can see roadway features, objects in the roadway, or pedestrians ahead is li mi ted by the headlamp intensity, ambient lighting, and presence or absence of oncoming headlamp glare.
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Discussion Visibility during nighttime driving in rural environments can be challenging for drivers. Often there is little or no ambient lighting to enhance the illumination of the roadway or objects thereon.
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DAYTIME LIGHTING REQUIREMENTS FOR TUNNEL ENTRANCE LIGHTING Introduction This guideline provides recommendations for minimum lighting requirements at the entrances of tunnels under daylight conditions. Visibility of low-visual-contrast objects can be challenging for drivers due to glare, large differences in illumination, and visual adaptation issues associated with the tunnel entrance.
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Di scu ssi on Lighting of tunnel entrances requires special consideration because of how drivers' visual system s respond to the uni que light in g conditions that occur at these entrances. In particular, there are driver performance issues related to illu mi nation levels in tunnel entrances.
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COUNT ER ME AS UR ES FO R IMPRO VI NG PEDES TR IA N CONSP IC UI TY AT CROSSW AL KS In tr od uc ti on Countermeasures for improving pedestrian conspicuity at crosswalk s refers to treatments that use flashing lights and beacons at midblock and intersection crosswalks. These lighting treatments do not necessarily improve visibility of pedestrians; rather, they are used to alert drivers to the presence of pedestrians in the crosswalk.
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Di scu ssi on In-pavement flashing lights, sign-m ounted flashing beacons, and flashing LEDs mounted in "Pedestrian Crossing" warning signs (in-sign flashing lights) have been shown to improve the safety at pedestrian crosswalks.
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C HARACTERISTICS OF LIGHTING THAT ENHANCE PEDESTRIAN VISIBILITY Introduction This guideline addresses characteristics of luminaires at midblock and intersection crosswalks as well as for general street lighting that will enhance the visibility of pedestrians in or near th e roadway. Factors that affect visibility under street lighting include intensity and color spectrum of the light source; reflectivity and color of the pedestrian clothing; reflectivity of the road surface; and whether the pedestrian is seen with periphera l or foveal vision.
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Di scu ssi on The issues associated with visibility of pedestrians at ni ght under street lighting are complex. Drivers mu st detect pedestrians under me sopic lighting levels, at which both the rod and cone receptors in the retina support vision ( 6 )
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C HARACTERISTICS OF EFFECTIVE LIGHTING AT INTERSECTIONS Introduction Characteristics of effective lighting at intersectio ns refers to lighting characteristics that facilitate visibility at intersections while avoiding detrimental effects of glare from luminaires. Although vehicle head lamps provide some measure of illumination, additional fixed lighting is often required to provide light levels and contrast that are satisfactory for safe visibility at intersections.
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Di scu ssi on A minimu m level of illumination is required in the driving environment for drivers to visually detect pedestrians, obstructions, intersection features, and other vehicles in order to safely cross or turn at an intersection at night. Although vehicle headlamps provide some measure of illumination, additional fixed lighting is often required to provide light levels and contrast that are satisfactory for sa fe visibility at intersections.
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