National Surface Transportation Safety Center for Excellence Reports (NSTSCE, VTTI)

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Bicycle Visibility: Conspicuity of Bicycle Headlamps, Tail Lamps, and Retroreflective Garments in Nighttime Roadway Environments
Bhagavathula, Rajaram; Gibbons, Ronald B.; Williams, Brian M.; Connell, Caroline A. (National Surface Transportation Safety Center for Excellence, 2020-07-21)
Cyclist deaths are overrepresented among traffic fatalities, and increasing cyclist conspicuity to drivers could potentially reduce cyclist deaths, particularly at night. This report describes an experiment with various commercially available bicycle visibility-enhancement systems in terms of their conspicuity to drivers during the day and at night. Visibility enhancements included a headlamp, tail lamp, spoke lights, and retroreflective clothing, including garments that highlight biomotion. The results indicate that active visibility treatments, such as bicycle-mounted lights, make cyclists more conspicuous than passive systems like retroreflective vests and biomotion bands. Flashing headlamps and tail lamps were the most conspicuous treatments during both the day and at night; fast flashing headlamps (6.7 Hz) had higher detection distances and rates during the day, and moderately fast flashing headlamps (3.4 Hz) had higher detection distances and rates at night. Spoke lights and flashing tail lamps, along with retroreflective vests, also aided cyclist visibility during the day and at night, especially for vehicles approaching intersecting cyclists. Passive retroreflective visibility treatments were most effective at night, when the vehicle was passing the cyclist from behind. However, that approach also used reflectors, so the discrete effect of passive retroreflective treatments could not be determined. This study also found that biomotion markers alone do not significantly increase cyclist conspicuity in visually complex natural environments. For most approaches, flashing lights had greater detection distances than biomotion markers, which in turn had higher detection rates than headlamps and tail lamps.
Crosswalk Lighting Using Narrow Beam Illuminator
Palmer, Matthew; Bhagavathula, Rajaram; Kassing, Andrew (National Surface Transportation Safety Center for Excellence, 2022-12-09)
This project’s main objective was to collect and analyze preliminary data regarding the safety benefits of additional narrow beam crosswalk lighting in a naturalistic environment. Experiment participants operated vehicles while confederate pedestrians (child-sized mannequins) were staged at various positions with or without overhead lighting and crosswalk lighting that used a commercially available narrow beam LED (light emitting diode) luminaire. Salex loaned the crosswalk lighting illuminator (CWI) luminaires to the Virginia Tech Transportation Institute for the experiment. When used with overhead lighting, the CWI increased the detection distance of the confederate pedestrians in the crosswalk to 297 m while only increasing the power consumption by 5%. This was nearly double the 160-m detection distance for the highest illuminance overhead only baseline condition. The experiment showed no benefit to using the CWI lighting alone. The results reaffirm that the direction of lighting is significant, but it is only one factor. Merely increasing light levels may not increase visual performance, just as changing the direction may not increase performance. The difference in the location of the illuminators and the overhead lights results in the light coming from different directions and illuminating the pedestrians and the background (roadway) differently than either alone. The effect on pedestrian contrast should be investigated further before setting illuminance levels for CWI lighting. Even with that caveat, the addition of a narrow beam CWI improves driver visual performance at detecting pedestrians in a midblock crosswalk by 88%. This is a powerful finding that should be considered as a safety treatment for midblock crosswalks.
Development of a Nighttime Visual Performance Model by Examining Distributions of Detection Distances
Bhagavathula, Rajaram; Gibbons, Ronald B. (2023-12-22)
Modeling the visual performance of drivers at night is complex. In addition to factors like luminance, contrast, observer age, and object size, research has shown that the motion of the object and the expectancy of the observer play an important role in the observer’s ability to detect an object on the roadway at night. Thus, it is important for a visual performance model to account for these factors. However, accounting for these factors could result in highly complex models, as accurately measuring driver expectancy and attention is difficult. A probabilistic approach to modeling nighttime driver visual performance could offer promise. In a probabilistic modeling approach, the variable of interest is treated as a random variable and the probability distribution of this variable is studied as a response to different conditions. In the case of night driving, we propose to use the detection distance of an object (such as a pedestrian) as the variable of interest. Detection distance is a measure of the reaction time of the driver. By studying the distribution of detection distances of objects under different lighting conditions, we can accurately understand the change in the detection probability of an object as a driver approaches an object. The current report had two goals. The first goal was to test if the detection distance distributions are accurately defined by the Weibull distribution. The second goal was to understand how different light levels affect the detection distance distributions of a child-sized mannequin. This was accomplished by performing a distribution analysis involving fitting a Weibull distribution to the detection distance data. The distribution fit will indicate how parameters like shape and scale vary across different conditions and their practical impacts on driver visual performance. The results of the study showed that the Weibull distribution could be used to fit the detection distance data, and that changing the light level definitely influenced the parameters of the distribution. An increase in light level increased the scale parameter and caused the detection distance distribution to stretch out from the pedestrian’s location. The results of the study also showed that both the scale and shape parameters could be used to compare the effectiveness of different lighting systems or interventions. The survivor functions of the detection distance data from the fitted Weibull distribution could be used to compare the effectiveness of a lighting system or a countermeasure by calculating the percentage of the population that detected the pedestrian from a distance greater than the stopping sight distance.
Effectiveness of Lighted Work Zone Apparel: Effects on Visibility
Bhagavathula, Rajaram; Kassing, Andrew; Gibbons, Ronald B.; Medina, Alejandra (National Surface Transportation Safety Center for Excellence, 2022-11-11)
In United States, collisions between vehicles and workers in a work zone are a major problem. In 2020, there were 157 worker fatalities in work zone in the United States. Increasing worker conspicuity has the potential to reduce to fatalities by making them more visible to motorists. Retroreflective vests (Class 3) and trousers (Class E) worn by workers in a nighttime work zone are passive in nature; i.e., they require light from oncoming vehicle headlamps to work. The advancement of LED technology has made it easy to install them on retroreflective vests and hard hats to increase their conspicuity. Multiple configurations of LEDs and flash patterns installed on vests and hard hats could be used to increase worker conspicuity. Further, equipment manufacturers are now offering work zone apparel and head protection which incorporate lights into portions of the retroreflective material, or adds light to a specific piece of equipment (hard hats). One of the major benefits is that these do not require external light sources for activation whereas retroreflective material relies on an eternal light source. According to manufacturers, the new apparel and equipment improve visibility, and the pieces are washable. There is also the potential for lighted apparel that uses colors or operating features (such as flash patterns) to further increase worker conspicuity. However, a typical work zone is a visually cluttered with flashing lights on work vehicles. Therefore, it is important that the selected configuration of lights on workers apparel are not masked by the visual clutter in the work zone. The conspicuity of passive (retroreflective material only) and active (both retroreflective and LEDs) apparel in a work zone will help in determining the apparel that would increase the conspicuity of the workers in the work zone. The goal of the current study is to evaluate effectiveness of lighted work zone apparel under realistic conditions. More specifically, the goal is to compare the effectiveness of various kinds of lighted worker apparel (colors, flash patterns, lighted hard hat, etc.) to that of standard retroreflective material under varying visually cluttered conditions. In the current study, the effects of worker apparel and scene clutter on driver visual performance were evaluated under realistic work zone conditions. Driver visual performance was measured indirectly using the detection distance of work-zone workers as indicated by participants as they drove through the simulated work-zone environment. The results of the current study show that lighted worker vests and helmet-mounted lights plays a critical role in increasing the conspicuity of workers in active nighttime work-zone environments with visually cluttered environments. Lighted work-zone vests with white-colored LEDs paired with helmet-mounted LEDs (also white colored), either in flashing or in a steady-on condition, had the longest detection distances. Standard Class 3 retroreflective vests had the lowest detection distances among all the garments evaluated. When workers wore the lighted apparel with red and white LEDs without the lighted helmet, the detection distances were shorter than with the lighted helmet but longer than with the retroreflective vest alone. Based on these results, a combination of lighted garments along with a lighted helmet, preferably in a flashing pattern or steady-on, are recommended to increase the conspicuity of workers in active nighttime work-zone environments.
Identification of factors related to violation propensity: mining the data of the Franklin intersections
Doerzaph, Zachary R.; Bhagavathula, Rajaram (National Surface Transportation Safety Center for Excellence, 2011-02-04)
This report describes an investigation of factors related to the prevalence of red-light violations at signalized intersections. A sample of 3,000 violators were compared to a matched set of compliant vehicle approaches using a logistic regression model. The focus was on identifying and exploring causal factors with the aim of assisting efforts to discover potential strategies for mitigation.
Initial Investigation of Intersection Lighting
Bhagavathula, Rajaram; Gibbons, Ronald B. (National Surface Transportation Safety Center for Excellence, 2022-10-31)
Nighttime crashes at intersections are a major traffic safety concern in the United States. Although providing lighting at intersections has proved to be a successful intervention against night crashes, current approaches to designing lighting at intersections are relatively simplistic, based on recommending light levels. These light levels stem from research that evaluated the effect of intersection lighting on night crashes, which does not account for the role of a driver’s visual performance or the effects of vehicle headlamps. For effective lighting design at intersections, empirical research is required to evaluate the effects of intersection lighting design on a driver’s visual performance as well as perceived visibility and glare. The current study had two goals. The first was to quantify visual performance in three lighting configurations (illuminating the intersection box, approach, or both). The second was 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. Twenty-four participants completed the study, with equal numbers of younger (18–35 years) and older (65+) individuals. 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 an illuminance level of 8 and 12 lux. Visual performance was inferior in lighting configurations in which only the approach to the intersection or both the approach to the intersection and the intersection box were illuminated, and there was not consistent plateauing of visual performance in either condition. Increased performance with box lighting was likely due largely to the rendering of targets involved. Visual performance was reduced among older participants, though age-related differences were consistent across lighting configurations. These results have important implications for the design of intersection lighting at isolated or rural intersections. Specifically, results indicated 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.
Pedestrian Visibility in Roundabouts: Naturalistic Study of Driver Eye-Glance Behavior
Bhagavathula, Rajaram; Williams, Brian M.; Gibbons, Ronald B. (National Surface Transportation Safety Center for Excellence, 2019-04-16)
Roundabouts increase safety, but their safety effects on vulnerable road users are not as great as the safety effects for motor-vehicle drivers. Additionally, many motorists fail to yield to pedestrians at intersections and roundabouts, possibly because drivers do not see the pedestrians, crosswalk signage, and/or pavement markings. Eye-tracking technology has been used to quantify driver eye-glance behavior in a variety of driving contexts, but has yet to be applied to drivers in roundabouts with pedestrians. The exploratory research performed for this project attempted to shed light on driver visual behavior at roundabouts, and to examine the extent that drivers looked at pedestrians, with the ultimate goal of increasing pedestrian safety at roundabouts. A quasi-naturalistic experimental study was conducted and drivers’ mean fixation durations toward pedestrians located at crosswalks were measured at two different roundabouts while making three kinds of turn maneuvers (straight through, left turn, and right turn) under day and nighttime conditions. Three important findings were evident. First, the results show that the position of the vehicle within the roundabout (approach, entry, and exit) had a significant impact on drivers’ visual behavior toward pedestrians. Drivers looked at pedestrians longer when they (drivers) were at the approach portion of the roundabout and less at the entry and exit portions of the roundabout. Second, the number of lanes at the roundabout did not significantly affect the drivers’ fixation durations toward the pedestrians. Finally, the age of the drivers and time of day did not significantly influence fixation durations toward the pedestrians at the roundabouts.
Rural Intersection Lighting Safety Analysis
Bhagavathula, Rajaram; Gibbons, Ronald B.; Terry, Travis N.; Edwards, Christopher J. (National Surface Transportation Safety Center for Excellence, 2017-08-03)
Under the sponsorship of the National Surface Transportation Safety Center for Excellence (NSTSCE), this research studied the relationship between lighting level and the night-to-day (ND) crash ratio at rural intersections in the state of Virginia. Most existing research on intersection lighting indicates that the presence of lighting reduces night crashes. This study aimed to quantify the effect of lighting level and lighting quality on ND crash ratios at rural intersections. Lighting data were collected from 131 rural intersections in Virginia, and crash data for the intersections were obtained from the Virginia Department of Transportation (VDOT). Lighting data were collected using a Roadway Lighting Mobile Measurement System (RLMMS). Out of the 131 intersections, data from 99 intersections were used for the comparative analysis. Data from 32 intersections could not be used because of issues with lighting data (e.g., Global Positioning System, illuminance data dropouts). Negative binomial regression was used to model the crash and lighting data. The results showed that increasing the average horizontal illuminance at all the intersections (both lighted and unlighted) by one unit (1 lux) decreased the ND crash ratio by 7%. For the lighted intersections, the same increase in average horizontal illuminance decreased the ND crash ratio by 9%. The largest decrease in the ND crash ratio was for unlighted intersections, where a 1-lux increase in the average horizontal illuminance decreased the ND crash ratio by 21%. The average roadway luminance also had negative parameter estimates, indicating that an increase in average roadway luminance results in a lower ND crash ratio. Stop-controlled intersections had smaller ND crash ratios compared to signalized intersections. Intersections with a posted speed limit of less than or equal to 40 mph had lower ND crash ratios compared to intersections with a posted speed limit higher than 40 mph. Results also showed that most lighting levels at most rural intersections did not meet the standards recommended by the Illuminating Engineering Society of North America (IESNA).
Virtual Reality as a Tool to Evaluate Pedestrian Safety
Bhagavathula, Rajaram; Williams, Brian M.; Owens, Justin M.; Gibbons, Ronald B. (National Surface Transportation Safety Center for Excellence, 2020-06-25)
Virtual reality (VR) promises to be an effective tool to evaluate changes to the built environment that could improve safety for pedestrians. 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 the intention to cross an intersection, the estimation of the speed and distance of an approaching vehicle, and the perceived safety and risk of crossing a road. Results showed no statistical difference between the real and virtual environments for participants’ intention to cross, estimation of distances, and perceptions of safety and risk. Statistically significant differences between real and virtual environments were observed in the estimation of speed and measures of presence. These results indicate that at lower vehicle speeds (25 mph and lower) VR can be used as tool to evaluate pedestrian safety in built environments.
Work Zone Lighting’s Effect on Driver Visibility
Bhagavathula, Rajaram; Gibbons, Ronald B. (National Surface Transportation Safety Center for Excellence, 2019-06-05)
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 are not known. Understanding these relationships can help to develop illumination guidelines for work zones that can reduce glare for drivers. The goal of this project was 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 with varying mounting heights, offset distances, and number of light towers. 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 feet and closer to the roadway (in travel lanes than in the shoulder) result in decreasing drivers’ visual performance and increasing their discomfort glare. Portable light towers should be mounted at a height of at least 20 feet, and balloon light towers with higher wattage (4,000 watts and greater) and lumen output (400,000 lumens and greater) should be located at an offset distance of at least 10 feet from the roadway.

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