Ronald B Gibbons

Relationship of Vertical Illuminance to Pedestrian Visibility in Crosswalks

Twenty-six participants evaluated a series of crosswalk lighting designs by visually detecting objects at each crosswalk location while traveling in a moving vehicle. The research was performed on a closed test track under nighttime conditions while the participants were driving an SUV with regular halogen headlamps. The conditions included several vertical illuminance levels (6, 10, 20, and 30 lux), varied luminaire types [high-pressure sodium (HPS) and metal halide (MH)], and various target object types (pedestrian and surrogate objects). Only one age group of participants (66 years and older) was used for the study, with equal representation of males and females. The participants were asked to detect objects at each crosswalk location when they were confident an object was present. The results indicated that object detection distances changed on the basis of vertical illuminance level, luminaire type, and object type. Object detection distance for HPS was greatest at 30 vertical lux and for MH at 20 vertical lux. However, these results were moderated by the clothing color of the target object. When object color was considered, pedestrians in white clothing were identified earlier under the HPS lighting condition at 20 lux. Under the MH configuration, denim-clothed objects were detected earlier than black-clothed objects, especially at the 20-lux lighting level. The results suggest that a vertical illuminance level of 20 lux at crosswalk locations provides adequate levels for target object detection. In addition to benefiting from vertical illuminance, target objects that wore white clothing had detection distances superior to other object types of different clothing colors. Recommendations for crosswalk lighting configurations are further discussed.

Wet Night Visibility of Pavement Markings: A Static Experiment

Fifty-three participants evaluated the visibility of four different pavement marking materials under a simulated rain system operating at 0.8 in. (20 mm) of rain per hour at night while driving a vehicle on a closed test track. The conditions tested include a variable lighting condition, glare, pavement types, and two different vehicle types. The evaluation consisted of determining the detection distance of a start or an end point of a white 4-in. edge line. Results showed that lighting improved visibility and mitigated the effects of glare. Results also showed that the wet retroreflective tape provided the longest visibility distance, followed by equivalent performance of profile thermoplastic; large glass beads with standard paint provided the shortest visibility distance. The detection distance was compared with the retroreflective performance of the pavement marking technology. It was found that a log-linear relationship exists between the retroreflectivity and the detection distance. It was also found that the level of retroreflectivity provided by the materials tested did not provide adequate visibility distance for a sedan with a 2-s visibility time at speeds greater than 45 mph.

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.

Influence of Vertical Illuminance on Pedestrian Visibility in Crosswalks

This project investigated the lighting levels required for crosswalk illumination. The current European methods for lighting suggest a crosswalk lighting level of 40 vertical lux for ensured safety. Two major questions were studied: the required vertical illuminance level for adequate pedestrian visibility and the selection of an object that could act as a surrogate for the pedestrian. The vertical illuminance was determined from an experiment that measured the visibility of pedestrians at lighting levels of 5, 20, 40, and 60 vertical lux. During the experiment, a crosswalk scene was presented to the participants and the time taken for identification of an object was measured. In addition to the lighting level, the conditions used in the experiment were lamp type (metal halide versus high-pressure sodium), the presence of glare, the use of overhead lighting, and the type of pedestrian clothing (white, black, and denim). The study found that a lighting design level of 20 vertical lux is likely adequate for...

Selection and Application of Warning Lights on Roadway Operations Equipment

This report presents recommended guidelines for the selection and application of warning lights on roadway operations equipment. The recommended guidelines address the physical, functional, and performance requirements of the lighting system, recognize that the lighting system on these vehicles must be designed and laid out with consideration to the planned or expected vehicle usage, and provide technical information for use in developing procurement specifications for specific applications. The content of the report will be of immediate interest to maintenance professionals and others involved in specifying warning lights on roadway operations equipment.

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.

Evaluation of Impact of Modern Headlamp Technology on Design Criteria for Sag Vertical Curves

This paper includes a review of the current methodologies used in the design of sag vertical curves, a review of the changes in headlamp technologies, the results of a survey of practitioners and two visibility experiments, and conclusions. The review of the headlamp technology shows that, over time, headlamp technologies have increasingly limited the amount of light emitted above the horizontal axis of the headlamp. In addition to the regulatory impact, headlamp technologies such as visually optically aligned systems also limit the upward divergence of the light beam from the longitudinal axis of the vehicle (uplight). The practitioner survey found that very few deviations from AASHTO design methodologies were used. On the basis of the practitioner review, the potential to modify current methodologies is limited to the manipulation of the vehicle speed, deceleration, and change in angle of curvature. The results of the visibility experiments showed that participants detected objects at distances that were significantly shorter than the stopping sight distance (SSD), not only in sag vertical curves but also on flat roadway. This finding indicated that even if sag vertical curves were redesigned, visibility distance would still be shorter than SSD because the headlamps would be the limiting factor. A review of the potential modifications to the design of sag vertical curves (which were suggested in the responses to the practitioner survey) found that these changes would be inadequate to make up the difference between visibility distance and SSD.

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.

Guidelines for Nighttime Visibility of Overhead Signs

This report presents proposed guidelines for nighttime overhead sign visibility, formatted as a potential replacement for the current Chapter 10, Roadway Sign Lighting, in the 2005 AASHTO Roadway Lighting Design Guide. The research for the project was conducted in two phases. In the first phase, a closed-course study was conducted at the Virginia Smart Road at the Virginia Tech Transportation Institute. The goal of this study was to determine legibility distances for drivers in controlled conditions for three different sign legend and background configurations lit by either high pressure sodium or light emitting diode systems or they were unlit. In the second phase, an open-road study was conducted by the Texas AM San Antonio, Texas; and Orlando, Florida. The goal of the open-road study was to determine the effects of sign luminance and visual complexity on the distance at which a driver can read overhead signs and street signs. Both studies employed cohorts of recruited drivers evenly split in terms of gender and age. The closed-course study found that sign lighting does not significantly impact legibility distance of signs in rural and dark areas, suggesting that sufficient illumination for visibility was provided by headlamps. Using software developed for the open-road study, digital images were analyzed to quantitatively measure visual complexity in urban and suburban areas. Visual complexity of sign surroundings was found to reduce the distance at which a driver can correctly recognize information from signs, however, this effect can be countered by increases in the legend luminance. This report fully documents the research and includes four appendixes: Incremental Effects of Light Sources and Sign Sheeting on Legend Luminance for Overhead Guide Signs; Assessment of Background Complexity Using Digital Images of Roadway Scenes by Image Processing; Open-Road Study Details; and Guidelines for Nighttime Overhead Sign Visibility.