In part because of the potential for high levels of glare from work zone illumination, recommendations for light levels from work zone illumination systems are substantially higher than for levels used along roadways in non–work zone locations. In a two-part study, requirements for work zone illumination light levels were assessed. First, levels for workers varying in age from 20 to 60 years were evaluated with the relative visual performance model, with and without the presence of visibility-reducing glare. Except for the smallest, lowest-contrast tasks performed by the older workers, an illuminance of 10 lx resulted in visibility well above the threshold even in the presence of glare, and an illuminance of 30 lx resulted in suprathreshold visibility for these conditions as well. The results of these computational analyses were largely confirmed in a full-scale, outdoor field demonstration attended by transportation agency engineers and highway contractors. Together, the findings suggest that when lighting systems provide sufficient glare control, light levels do not always need to be especially high to ensure adequate visibility for workers.
Reducing the potential for crashes involving front line service workers and passing vehicles is important for increasing worker safety in work zones and similar locations. Flashing yellow warning beacons are often used to protect, delineate, and provide visual information to drivers within and approaching work zones. A nighttime field study using simulated workers, with and without reflective vests, present outside trucks was conducted to evaluate the effects of different warning beacon intensities and flash frequencies. Interactions between intensity and flash frequency were also analyzed. This study determined that intensitiesof 25/2.5 cd and 150/15 cd (peak/trough intensity) provided the farthest detection distances of the simulated worker. Mean detection distances in response to a flash frequency of 1 Hz were not statistically different from those in response to 4 Hz flashing. Simulated workers wearing reflective vests were seen the farthest distances away from the trucks for all combinations of intensity and flash frequency.
Recent developments in solid-state lighting, sensor, and control technologies make new configurations for vehicle forward lighting feasible. Adaptive driving beam (ADB) systems build on systems that automatically switch from high- to low-beam headlights in the presence of oncoming vehicles. ADB systems can detect oncoming headlights and preceding taillights and reduce their intensity only in the direction of the other lights, while they maintain higher levels of illumination throughout the remainder of the field of view. The nominal benefit of ADB systems is the provision of high-beam levels of illumination in the forward scene, while glare is reduced to oncoming and preceding drivers, who perceive low-beam illumination levels. In this study, two dynamic field experiments were conducted: one experiment measured the ability of observers to identify the walking direction of roadside pedestrian targets with and without the use of the ADB system; the other experiment evaluated the discomfort glare elicited by the ADB system compared with the glare from conventional low- and high-beam headlights. The findings from both experiments were consistent with previous analytical and static field tests and suggested that ADB systems can offer safety benefits beyond those offered by conventional headlight systems.
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