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SUMMARY Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections NCHRP Report 613: Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections ("the Guidelines") assists roadway planners, designers, and operators as they consider and select appropriate speed reduction treatments at intersections located in high- speed environments. The Guidelines are not a new standard for implementing treatments. Rather, they are informational, describing good practices for selecting treatments. These Guidelines were produced as a part of NCHRP Project 3-74, which studied speed reduction treatments for high-speed intersections. This project focused on physical treat- ments (geometry, signing, striping), rather than on enforcement. For the purposes of this report, high-speed intersections are defined as intersections where the posted speed limit is 45 mph or greater on one or more approaches. In some cases, speeds through the intersection proper may be greater than 45 mph (e.g., major street approaches at two-way, stop-controlled intersections). In other cases, speeds at the intersection may be closer to zero (e.g., signalized intersections approached on red). The driver workload and desired response vary with these conditions along with a vari- ety of other roadway and environmental features. To help Guidelines users select an appro- priate treatment, the Guidelines focus on providing an understanding of all the elements that may affect conditions at a high-speed intersection. Very little research has focused on speed at intersections, and most data relate to roadway segments. Furthermore, while much is surmised about the relationship between speed and safety, little data exist to clearly define this relationship. Finally, little data exist that isolate the effects of speed on overall intersection performance (safety, operations, and serving all modes). A wide variety of treatments is presented in the Guidelines. As part of this research effort, some of the treatments were tested to determine how effectively they reduce speeds. The results of these tests, as well as the results of other studies, are presented in the Guidelines. In most cases, the body of research is limited and the available data may be useful to roughly indicate the promise of a particular treatment, but are generally not sufficient to predict effectiveness in potential applications. Because of the lack of published data on this topic, the Guidelines focus on the principles affecting speed at intersections. The guidance provided to analyze the conditions that may affect driver behavior or may make a specific intersection particularly sensitive to speed are expected to be as useful as the data provided on each of the treatment types. The Guidelines are not intended as a new standard for implementing speed reduction treatments, but
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2 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections instead are presented as a reference guide that may be used in conjunction with local knowl- edge and professional judgment. Section 1 introduces the Guidelines and presents their purpose, scope, and applicability. Section 2 discusses the fundamentals of speed. Section 3 leads users through the process of considering and implementing speed reduction treatments on intersection approaches. Sec- tion 4 describes the speed reduction treatments in detail. Appendices A through D provide a treatment implementation process framework, scenario-based case studies, testing data and results from the testing plan, and references to other relevant studies, respectively.