Rajaram Bhagavathula

Role of Expectancy, Motion and Overhead Lighting on Nighttime Visibility

More than half of the pedestrian fatalities occur at night. It is important to understand the factors that lead to pedestrian detection for designing and implementing effective countermeasures in order to reduce pedes-trian fatalities. Research has shown that expectancy, motion and overhead lighting affect pedestrian visibil-ity. This goal of this study is to understand the combined effect of these three factors on nighttime visibil-ity. Twenty four participants were recruited to drive on a test track under different conditions of expectancy and overhead lighting. The participants were asked to identify static and moving objects. The results showed that as the level of expectancy increases the detection distances also increase. Moving objects were detected from farther than static objects and presence of overhead lighting also increased the detection dis-tances. Motion tends to draw more attention than expectancy when detecting new objects. These results have implications in the areas of pedestrian safety, novice driver training and work zone safety. They also reiterate the safety benefits of providing overhead lighting at high pedestrian-vehicle conflict areas.

Relationship Between Roadway Illuminance Level and Nighttime Rural Intersection Safety

Almost all existing research about intersection lighting indicates that the presence of lighting reduces nighttime crashes. This study aimed to quantify the effect of lighting level and lighting quality on the night-to-day (ND) crash ratios at rural intersections. Illuminance measurements were collected from 99 lighted and unlighted rural intersections in Virginia. The measurements were then combined with the crash data, obtained from the Virginia Department of Transportation, for each of the intersections. A negative binomial regression was used to model the crash and lighting data. Results indicated that lighting level (average horizontal illuminance) significantly affected the ND crash ratios at rural intersections. A 1 lux (lx) increase in the average horizontal illuminance at all rural intersections in Virginia corresponded to a 7% decrease in the ND crash ratio. For the lighted intersections, a 1 lx increase in average horizontal illuminance corresponded to a 9% decrease in the ND crash ratio. The largest decrease in the ND crash ratio was for unlighted intersections, where a 1 lx increase in the average horizontal illuminance corresponded to a 21% decrease. Stop-controlled intersections had smaller ND crash ratios than signalized intersections. Intersections with a posted speed limit of less than or equal to 40 mph had lower ND crash ratios than intersections with a posted speed limit of greater than 40 mph. Each of the results is discussed with respect to the impacts of the lighting measurements on nighttime driving safety and overall visibility.

Effects of Intersection Lighting Design on Nighttime Visual Performance of Drivers

ABSTRACT Nighttime crashes at intersections present a major traffic safety issue in the United States. Existing approaches to intersection lighting design do not account for a driver’s visual performance or the potential interactive effects of vehicle headlamps and roadway lighting. For effective design lighting at intersections, empirical research is required to evaluate the effects of lighting configuration (part of the intersection illuminated) and lighting levels on nighttime driver visual performance. The current study had two goals: First, to quantify visual performance in three lighting configurations (illuminating the intersection box, approach, or both) and second, to determine what lighting levels within each lighting configuration support the best visual performance. The study involved a target detection task completed at night on a realistic roadway intersection. Illuminating the intersection box led to superior visual performance, as indicated by longer target detection distances, fewer missed targets, and more targets identified within a safe stopping distance. For this lighting configuration, visual performance plateaued between 7 and 10 lx of mean intersection illuminance. These results have important implications for the design of intersection lighting at isolated/rural intersections, specifically that illuminating the intersection box is an effective strategy to increase nighttime visual performance for a wider range of driver ages and could also be an energy-efficient solution.

Effect of Work Zone Lighting on Drivers’ Visual Performance and Perceptions of Glare

Nighttime crashes at work zones are major concerns for construction workers and motorists. Although in a majority of the U.S. states, department of transportation specifications for work zone lighting mention that contractors should reduce glare for workers and drivers, only two states advocate detailed specifications like light positions, orientation, and light levels. Although some studies have examined the impact of glare from work zone lights on workers and others have calculated veiling luminance levels for drivers in the work zone, the effect of work zone lighting on drivers’ visual performance and glare perception has never been studied in a realistic setting. The goal of this study was to understand the impact of commercially available portable light towers (metal halide, LED, and balloon) and their orientation on drivers’ visual performance and their perceptions of glare. Participants drove through a realistic work zone simulated on the Virginia Smart Road. Visual performance was assessed by a detection task and perception of visibility and glare were assessed by questionnaires. Results indicated that the type of light tower and its orientation affect visual performance and perceptions of visibility and glare. Light towers aimed toward the driver resulted in lowering drivers’ visual performance, both objectively and subjectively. When the light towers were aimed away from or perpendicular to the driver, the visual performance was higher and the differences in visual performance between the types of light towers were minimal. These findings indicate that these orientations should be preferred for work zone light towers.

Effects of Mounting Height, Offset Distance, and Number of Light Towers on Drivers’ Visual Performance and Discomfort Glare in Work Zones

Portable light towers are a significant source of glare to motorists entering a work zone. Although existing research has evaluated the effect of light tower orientation on visibility and glare, the effects of factors like mounting height, offset distance from the roadway, and number of light towers in the work zone, on visual performance and discomfort glare is not known. Understanding these relationships can help in developing illuminating guidelines for work zones that can reduce glare for drivers. The goal of this paper is to understand the effect of mounting height, offset distance to the roadway, and number of light towers in the work zone on drivers’ visual performance and discomfort glare. Participants drove through a realistic work zone and evaluated portable light towers in varying mounting heights, offset distances, and number of light towers in the work zone. Results showed that the mounting height and offset distances play a critical role in affecting the driver’s visual performance and discomfort glare rating. Portable light towers, irrespective of wattage and lumen output, at lower than a mounting height of 20 ft and closer to the roadway result in decreasing driver visual performance and increasing their discomfort glare. Portable light towers should be mounted at a height of at least 20 ft and balloon light towers with higher wattage (4,000 W and greater) and lumen output (400,000 lumens and greater) should be located at an offset distance of at least 10 ft from the roadway.

The Reality of Virtual Reality: A Comparison of Pedestrian Behavior in Real and Virtual Environments

Virtual reality (VR) can be a very effective tool to evaluate built environment to support improvement of pedestrian and other vulnerable road user safety. However, in order to draw actionable conclusions from VR it is important to understand the degree to which pedestrians’ perceptions and behaviors match across real and virtual environments. In this study, participants experienced equivalent real and virtual environments and performed similar tasks in each. Tasks included pedestrian’ intention to cross, estimation of speed and distance of an approaching vehicle, and the perceived safety and risk of crossing a road. Pedestrians’ presence was also measured in all environments. Result showed that there were no differences between the real and virtual environments for most of the tasks. Significant differences between real and virtual environments were observed in the estimation of speed and measures of presence. These results have important implications for using VR as tool to evaluate pedestrian safety in built environments.