A Metric for Sustainable Roadway Lighting Design Configuration

Road lighting standards are developed to improve night-time visibility and to assist drivers in their visual tasks. Most countries use the ANSI/IESNA recommended practice RP-8-14 or CIE Publication 115. These standards aim at illuminating road pavements by specifying targets of horizontal illuminance or luminance values at the pavement level. However, a sustainable road lighting standard should encompass all of what could be important for drivers to see. This includes the pavement and any obstacles on the road or in close proximity to the road. The objective of this manuscript is to investigate how to improve the configurations of the design variables in the current road lighting standards aiming at providing a sustainable visual environment for drivers during nighttime. The study used several techniques such as data collection, data analysis, and computer simulation. The tested metric was the contrast. The location and distribution of targets depended on the possible location of obstacles. We developed a new metric that we named “mean contrast”. The analysis discussed in this paper includes four possible target heights, three pole spacings, five lateral target locations, and sixteen longitudinal locations of measuring points. Results showed that targets at low height (0.05 m and 0.5 m) exhibited negative contrast, while those at 1.0 m and above showed positive contrast. The negative mean contrast did get affected by pole spacing, while the positive mean contrast at 1.5 m became lower as the spacing increased. The positive and negative uniformity also dropped with larger pole spacings. We conclude that the mean contrast metric has merit and could be used to provide a better visual environment for drivers during night-time.