Session: 14-04-01: Reliability and Safety in Transportation Systems

Paper Number: 71215

Start Time: Tuesday, 10:35 AM

71215 - A Systematic Study of Pedestrian Contrast and Detection From Vehicle Headlights 

An important factor in evaluating the visibility of pedestrians at night is the contrast they offer an observer. This paper investigates and quantifies the influence of various parameters on contrast. For a pedestrian to be visible or detectable under nighttime conditions, the contrast between the illuminated pedestrian and their background must be sufficient. Models are available to quantify contrast and visibility levels and include theoretical models or computer-based models. The goal of these models is to calculate contrast from luminance data, size, distance, observation time, and other parameters to predict visibility levels on the basis of contrast thresholds, age, and other factors. The luminance measurements for a given reflectance and illumination as well as visibility level calculations for a given background can be carried out with discriminating accuracy if the three-dimensional characteristics of the headlight illuminance, the luminance at the location of interest on the pedestrian’s body as well as the lateral and longitudinal position of the pedestrian are available.

An experiment was conducted using pedestrians or surrogate human models positioned along a grid in relation to the illuminated headlights of vehicles positioned on a dry asphalt roadway with no additional overhead lighting. As part of this experiment, headlight illuminance was mapped, and pedestrian luminance data were comprehensively collected to provide parametric data necessary to evaluate patterns affecting contrast. Luminance and illuminance data are presented in the form of three-dimensional plots and further related to visibility levels using the Adrian model.

The results of this study highlight and quantify important factors to understand visibility of pedestrians at night. These include position of the pedestrian both longitudinally and laterally, reflectivity of the clothing, vertical variations in luminance and illuminance, the background, and headlamp characteristics. They emphasize that three-dimensional modeling of headlight illuminance and pedestrian luminance enhances the understanding of pedestrian contrast and visibility.

The use of a photometer and a detailed analysis of the headlight data allowed this study to gain specific insights. The photometer records the combined effect of headlight illuminance levels and the reflectance of the clothing thus allowing a realistic, as opposed to theoretical, understanding of a given contrast configuration of a pedestrian against a given background. The methodology also allows accounting for the three-dimensional aspects of humans as it relates to body curvatures and the way they reflect light. While this study is limited to two headlight systems it is apparent that the headlight beams are not continuous, symmetrical, or well-behaved functions when viewed in three dimensions. More work with more headlight systems could be envisioned to better conclude systematically on their effect on pedestrian VL but this study outlines the complexity of headlight beam configurations on VL. This study was also limited to a single dark background and it is evident that multiple options of a lit background, overhead streetlights, or other situations including glare sources would add to the variations in VL. But the methodology presented here remains useful as it lays out a model for pedestrian analysis where all factors can be accounted for with a greater level of detail and differentiation.

Presenting Author: Fawzi P. Bayan SEA, Ltd.

Authors:

Fawzi P. Bayan SEA, Ltd.
Thomas A. Timbario SEA, Ltd.
Jonathan D. Nelson SEA, Ltd.
Stuart Sheldon II SEA, Ltd.
Ronny E. Wahba SEA, Ltd.
Brandon Keys SEA, Ltd.