An increasing amount of highway repair and construction work is being performed during the off-peak nighttime hours. Nighttime construction is advocated as a way to mitigate the impact of construction operations on the traveling public, shorten the duration of construction operations, and reduce the potential for work zone accidents. However, the utilization and placement of lighting equipment to illuminate the work zone may cause harmful levels of glare for the traveling public. This type of nighttime glare needs to be controlled and minimized to ensure safety for the traveling public and construction workers. This research study focused on studying the veiling luminance ratio (glare) experienced by drive-by motorists in lanes adjacent to nighttime work zones.The major objectives of this study are to: (1) provide an in-depth comprehensive review of the latest literature on the causes of glare and the existing practices that can be used to quantify and control glare during nighttime highway construction; (2) identify practical factors that affect the measurement of veiling luminance ratio (glare) in and around nighttime work zones; (3) analyze and compare the levels of glare and lighting performance generated by typical lighting arrangements in nighttime highway construction; (4) evaluate the impact of lighting design parameters on glare and provide practical recommendations to reduce and control lighting glare in and around nighttime work zones; (5) develop a practical model that can be utilized by resident engineers and contractors to measure and quantify veiling luminance ratio (glare) experienced by drive-by motorists near nighttime highway construction sites; and (6) investigate and analyze existing recommendations on the maximum allowable levels of veiling luminance ratio (glare) that can be tolerated by nighttime drivers from similar lighting sources. In order to achieve these objectives, the study was conducted in four major tasks that focused on: (1) conducting a comprehensive literature review; (2) visiting and studying a number of nighttime highway construction projects; (3) conducting field studies to evaluate the performance of selected lighting arrangements; and (4) developing practical models to measure and control the levels of glare experienced by drive-by motorists in lanes adjacent to nighttime work zones.In the first task of the project, a comprehensive literature review was conducted to study the latest research and developments on veiling luminance ratio (glare) and its effects on drivers and construction workers during nighttime highway construction work. Sources of information included publications from professional societies, journal articles, on-line databases, and contacts from DOT???s. The review of the literature focused on: (1) lighting requirements for nighttime highway construction; (2) causes and sources of glare in nighttime work zones, including fixed roadway lighting, vehicles headlamps, and nighttime lighting equipment in the work zone; (3) the main types of glare which can be classified based on its source as either direct or reflected glare; and based on its impact as discomfort, disabling, or blinding glare; (4) available procedures to measure and quantify discomfort and disabling glare; (5) existing methods to quantify pavement/adaptation luminance which is essential in measuring discomfort and disabling glare; (6) available recommendations by State DOTs and professional organizations to control glare; and (7) existing guidelines and hardware for glare control.The second task involved site visits to a number of nighttime work zones to identify practical factors that affect the measurement of the veiling luminance ratio in nighttime construction sites. The site visits were conducted over a five-month period in order to gather data on the type of construction operations that are typically performed during nighttime hours, the type of lighting equipment used to illuminate the work area, and the levels of glare experienced by workers and motorists in and around the work zone. One of the main findings of these site visits was identifying a number of challenges and practical factors that significantly affect the measurement and quantification of the veiling luminance ratio (glare) in nighttime work zones. These practical factors were carefully considered during the development of the glare measurement model in this study to ensure its practicality and ease of use in nighttime work zones by resident engineers and contractors alike. Another important finding of the site visits was the observation that improper utilization and setup of construction lighting equipment may cause significant levels of glare for construction workers and drive-by motorists.In the third task, field experiments were conducted to study and evaluate the levels of lighting glare caused by commonly used lighting equipment in nighttime work zones. During these experiments, a total of 25 different lighting arrangements were tested over a period of 33 days from May 10, 2007 to June 12, 2007 at the Illinois Center for Transportation (ICT) in the University of Illinois at Urbana-Champaign. The objectives of these experiments were to: (1) analyze and compare the levels of glare and lighting performance generated by typical lighting arrangements in nighttime highway construction; and (2) provide practical recommendations for lighting arrangements to reduce and control lighting glare in and around nighttime work zones. The field tests were designed to evaluate the levels of glare and lighting performance generated by commonly used construction lighting equipment, including one balloon light, two balloon lights, three balloon lights, one light tower and one Nite Lite. The tests were also designed to study the impact of tested lighting parameters (i.e., type of light, height of light, aiming and rotation angles of light towers, and height of vehicle/observer) on the veiling luminance ratio experienced by drive-by motorists as well as their impact on the average horizontal illuminance and lighting uniformity ratio in the work area. Based on the findings from these tests, a number of practical recommendations were provided to control and reduce veiling luminance ratio/glare in and around nighttime work zones.The final (fourth) task of this study focused on the development of a practical model to measure and quantify veiling luminance ratio (glare) experienced by drive-by motorists in lanes adjacent to nighttime work zones. The model was designed to consider the practical factors that were identified during the site visits, including the need to provide a robust balance between practicality and accuracy to ensure that it can be efficiently and effectively used by resident engineers on nighttime highway construction sites. To ensure practicality, the model enables resident engineers to measure the required vertical illuminance data in safe locations inside the work zone while allowing the traffic in adjacent lanes to flow uninterrupted. These measurements can then be analyzed by newly developed regression models to accurately calculate the vertical illuminance values experienced by drivers from which the veiling luminance ratio (glare) can be derived. This task also analyzed existing recommendations on the maximum allowable levels of veiling luminance ratio (glare) that can be tolerated by nighttime drivers from various lighting sources, including roadway lighting, headlights of opposite traffic vehicles, and lighting equipment in nighttime work zones.The main research development of this study contribute to the advancement of current practice in highway construction and can lead to an increase in the safety of construction workers and the traveling public in and around the nighttime work zones. The outcome of this study will help in: (1) identifying practical factors and challenges that affect the measurements of glare in and around nighttime work zones; (2) evaluating and comparing the lighting performance and glare levels of typical construction lighting equipment that are commonly used in nighttime highway construction projects; (3) recommending practical lighting arrangements that generate acceptable levels of lighting glare for motorists and adequate levels of lighting performance for construction workers inside the work zone; (4) developing practical and safe model for measuring and quantifying the veiling luminance ratio experienced by drive-by motorists near nighttime highway construction sites; and (5) providing a baseline for Departments of Transportation (DOTs) to develop specifications and standards on how to control and quantify the levels of glare in nighttime highway construction projects.
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