Does the Interaction between Vehicle Headlamps and Roadway Lighting Affect Visibility? A Study of Pedestrian and Object Contrast

Abstract

Vehicle headlamps and roadway lighting are the major sources of illumination at night. These sources affect contrastdefined as the luminance difference of an object from its backgroundwhich drives visibility at night. However, the combined effect of vehicle headlamps and intersection lighting on object contrast has not been reported previously. In this study, the interactive effects of vehicle headlamps and overhead lighting on object contrast were explored based on earlier work that examined drivers' visibility under three intersection lighting designs (illuminated approach, illuminated box, and illuminated approach + box). The goals of this study were to: 1) quantify object luminance and contrast as a function of a vehicle's headlamps and its distance to an intersection using the three lighting designs; and, 2) to assess whether contrast influences visual performance and perceived visibility in a highly dynamic intersection environment. Both luminance and contrast of roadway visibility targets and a pedestrian were measured with a calibrated photometer at a realistic intersection. Both target and pedestrian contrast and luminance were substantially affected by the intersection lighting configuration, illuminance level, location at the intersection, and vehicle distance from the intersection. Objects also underwent changes in contrast polarity (positive to negative or vice-versa) as the distance between the vehicle and object changed. During these polarity transitions, objects became invisible because the contrast was zero. Negative contrast on targets was associated with higher visual performance. Within a given contrast polarity (positive vs. negative), visual performance depended on the magnitude of contrast, with higher contrast associated with higher visual performance. The relationship between pedestrian contrast and perceived visibility was complex, since pedestrians were often rendered in multiple contrasts. These findings have important implications for the lighting design of intersections and the development of nighttime pedestrian detection systems that rely on computer vision

Influence of automotive headlamp systems on the visibility of targets under different road lighting conditions

“…In the worst cases, combined illumination by both systems rendered the targets invisible when background luminance and target luminance met. This camouflage effect has been observed previously by Bacelar, 28 Gibbons et al 30 and Bhagavathula et al 31 However, the road lighting plays a significant role in illuminating the road for other traffic participants such as pedestrians or cyclists and is therefore mandatory for urban scenarios.…”

“…There is previous research on this topic by Bacelar, 28 Ekrias et al , 29 Gibbons et al 30 and Bhagavathula et al 31 Bacelar measured the loss in visibility of square targets (200 mm wide, 20% reflectance) when using road lighting and headlamps. However, this used only one road lighting scenery with a high luminance (2.45 cd/m 2 ), the reflectance of the targets was fixed and only two distances (40 m and 90 m) were investigated.…”

Lighting Strategies to Increase Nighttime Pedestrian Visibility at Midblock Crosswalks

“…These results reinforce results of earlier studies [9,33], which argued that rendering a pedestrian in positive contrast will increase their visibility. Positive contrast lighting designs could aid in pedestrian visibility as these could provide vital clues about the direction of the pedestrians' travel by discerning features such as hands, face, etc., unlike negative contrast, which only renders the pedestrians as silhouettes, making the feature discrimination difficult [30,34]. These results indicate that a vertical illuminance of at least 10 lux on the pedestrian at the entrance of the crosswalk when the luminaire is located in front of the crosswalk will increase pedestrians' visibility to approaching drivers.…”

“…It should be noted that the representations in Figure 1 are not photometrically accurate and are merely illustrations to show the location of the luminaires with respect to the crosswalk. Further, in realistic roadway conditions, contrast is never constant and changes as a function of the distance between the observer's vehicle and the pedestrian at the crosswalk [30]. Thus, it would be very difficult to establish a contrast metric for pedestrians at crosswalks.…”

Required Visibility Level for Reliable Object Detection during Nighttime Road Traffic in Non-Urban Areas

“…Contrast polarity also affects the threshold luminance difference required for object detection [15,18,36]. Studies by Aulhorn [15] and Damasky [18] demonstrate that the threshold luminance difference for positive and negative contrast is of the same magnitude but lower for negative contrast than for positive contrast.…”