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2 Background The question of whether and to what extent roadway lighting improves traffic safety has been studied extensively in recent decades. In general, the consensus is that, when used appropriately, roadway lighting results in reductions in the frequency and severity of nighttime crashes (Rea etÂ al. 2009). On the other hand, there is a growing recognition that outdoor lighting can have some nega- tive consequences for the natural environment and possibly for human health as well (McColgan 2003). Nor are these negative consequences limited to urban areas where the concentration of lighting tends to be greatest. When adjusted on a per capita basis, light pollution in rural areas is revealed to be as significant an issue as it is in urban locations (Poon 2020). Consequently, it is impor- tant to use roadway lighting when and where it can be most effective; this is especially true when public budgets for roadway safety are stretched thin. The present synthesis report addresses one specific roadway lighting applicationâthe illumina- tion of isolated rural intersections. To help transportation agencies understand the benefits of and to develop practices for isolated rural intersection lighting that optimize safety benefits against its costs and potential negative impacts, this report is a compilation of existing practices and relevant research. The synthesis also identifies gaps in collective information so that future research activi- ties related to lighting for isolated rural intersections can be complementary and not redundant with existing knowledge. The glossary (AppendixÂ A) lists technical terms used throughout to help the reader understand basic lighting terminology. Sometimes, more than one term can be used to express a concept, and the glossary contains entries to help agencies that may use one term understand what is meant when other terms are used by other agencies or researchers. Method Two primary methods were used to develop this synthesisâa literature search and a survey of state transportation agencies regarding their experiences with lighting for isolated rural intersections. Literature Search The literature survey focused on three primary sources of information. Research reports and studies of lightingâs impacts and effects, particularly along rural/isolated intersections, were located through sources such as the Transportation Research International Documentation (TRID) data- base, as well as academic search tools like Google Scholar and Scopus, and the websites of major academic publishers. State and local transportation agency policies and guidelines for roadway C H A P T E R 1 Introduction
Introduction 3Â Â lighting were searched online. Finally, databases such as Google News and Gale News and Refer- ence were searched for news stories discussing projects involving lighting at isolated rural inter- sections. Although news stories might only contain partial information about the effectiveness of safety treatments such as lighting, such stories are often useful for gathering information about initial costs and the underlying reasons for considering lighting and alternatives to lighting. The primary source of information in the literature review was from reports and practices published by state departments of transportation. When relevant, information from local munici- palities (defined in this report as counties, cities, towns, or villages) has been included. Survey Questionnaire A questionnaire asking state transportation agencies for input about their experience with lighting for isolated rural intersections, practices, and criteria used in the design of lighting for these facilities was developed (see AppendixÂ B). The survey was implemented in the online survey website SurveyGizmo. Individuals from AASHTO who participate on the Joint Technical Committee on Roadway Lighting or the joint committeeâs parent committees (the Committee on Design and the Committee on Traffic) were contacted to ask if they would be willing to take the online survey. After agreeing to participate, a few individuals reported that they could not access the survey because of network restrictions within their agencies. A second copy of the survey was implemented on the website eSurveysPro; some participants used this website to respond to the questionnaire. Some individuals were unable to respond on either website and used a Microsoft Word document with the questionnaire to provide their responses. Representatives from 51 state/district transportation departments were invited to participate in the survey. In total, 44 completed survey responses were received, a response rate of 86%. AppendixÂ C lists the agencies participating in the survey. Report Content The subsequent chapters of this report present the following topics: â¢ Warranting Issues: This chapter provides a synopsis of policies and decision-making approaches used to determine where and when rural intersection lighting should be installed. These policies and approaches are based on factors such as roadway geometry, facility type, traffic volume, crash history, and pedestrian use. â¢ Design Factors and Criteria: This chapter focuses on the design-related factors and criteria used to develop lighting designs and to evaluate the performance of lighting for isolated rural intersections. â¢ Impacts: This chapter discusses the impacts of isolated rural intersection lighting as experi- enced by transportation agencies, including impacts on safety and potential negative impacts such as light pollution. â¢ Installation, Operations, and Maintenance: This chapter describes factors related to the implementation of isolated rural intersection lighting, providing transportation agencies with information to help them anticipate issues as agencies deploy these systems. â¢ Economics: This chapter discusses the economic impacts of isolated rural intersection lighting, initial costs for equipment and installation, and energy and maintenance costs. â¢ Conclusions, Knowledge Gaps, and Research Needs: This chapter highlights the primary find- ings of this synthesis report, including an overview of knowledge gaps and areas where further research might be performed. â¢ Case Examples: This chapter presents several examples from state transportation agencies of isolated rural intersection lighting installations as well as alternatives to lighting.