Over the last two decades, an increasing number of highway construction and maintenance projects in the United States have been completed at night to avoid or alleviate traffic congestion delays. Working at night entails several advantages, including lower traffic volumes, less impact on local businesses, cooler temperatures for equipment and material, and fewer overall crashes. Although nighttime roadway operations may minimize traffic disruptions, there are several safety concerns about passing motorists and workers in the nighttime work zone. For instance, improper lighting arrangements or excessive lighting levels at the job site could cause harmful levels of glare for the traveling public and workers, which can lead to an increased level of hazards and crashes in the vicinity of the work zone.

To address the issue of glare, the current report focuses on determining and evaluating disability glare on nighttime work zones in order to develop appropriate strategies for improving the safety of workers and motorists during nighttime highway construction and maintenance projects. Disability glare is the glare that impairs our vision of objects without necessarily causing discomfort, and it can be evaluated using the veiling luminance ratio (VL ratio). In this study, disability glare values were determined by using lighting data (vertical illuminance and pavement luminance measurements) from the testing of 49 lighting arrangements. Two LED balloon lights, a metal-halide light tower, and an LED light tower were utilized for the field lighting experiments. The glare assessment analyzed the effects of the lighting system setup’s parameters, such as the mounting height, power output, rotation angle, and aiming angle of luminaires on the veiling luminance ratio values (which is a criterion for limiting disability glare).

The study revealed the following key findings: (1) an increase in mounting heights of both balloon lights and light towers resulted in lower disability glare levels; (2) compared to the "perpendicular" and "away" orientations, orienting the light towers "towards" the traffic (45 degrees) significantly increases the disability glare levels of the lighting arrangement; and (3) increasing the tilt angles of portable light tower luminaries resulted in an increase in disability glare levels.

Report Number



daytime construction, nighttime construction, work zone safety, lighting, illuminance, pavement luminance, glare, veiling luminance, rolling slowdown, pacing operation, probe data, traffic simulation, traffic safety

SPR Number

4542 Volume 1

Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, IN

Date of this Version