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Suggested Citation:"Section 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2008. Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections. Washington, DC: The National Academies Press. doi: 10.17226/14162.
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Suggested Citation:"Section 1 - Introduction." National Academies of Sciences, Engineering, and Medicine. 2008. Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections. Washington, DC: The National Academies Press. doi: 10.17226/14162.
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Page 4

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Drivers generally choose a reasonable travel speed based on their perception of safety and comfort; a variety of conditions and circumstances, however, can lead a driver to misinterpret what is safe and comfortable and result in speeds that are undesirably high for the conditions present at a specific intersection approach. Some of these circumstances are human factors that may be unique to the individual driver and his or her behavior, and others are physical. Physi- cal changes to the roadway and surrounding environment may influence driver behavior, which can indirectly reduce speed and/or enhance environmental quality. These Guidelines provide relevant information about the effects of speed, the conditions that may contribute to undesirably high speeds at intersection approaches, and the state of the practice related to speed reduction treatments used in the United States and abroad—including their effec- tiveness and implementation considerations. The Guidelines also provide insights into the relationship between speed and facility operations. There are many popular beliefs about the rela- tionship between speed and safety, and it is common for people to assume a direct relationship between the two. In fact, there is little published data to actually link speed with safety performance. This report does not discuss whether speed reduction is appropriate for a condition or what amount of reduction is necessary. This document assumes that the user already desires reduced speeds. The Guidelines provide users with information about speed, speed considerations at intersections, and the potential application of treatments to affect speed. Additional research is needed to fully understand the effects that speed reduction treatments and reduced speed may have on safety. 1.1 Intended Users The Guidelines are designed to be useful to engineers, planners, students, and researchers. 1.2 Purpose of Guidelines The Guidelines provide information to help users select speed reduction treatments at inter- section approaches. Although the application of these treatments most often pertains to existing intersections that experience undesirably high speeds, the information also is relevant to new intersection designs. 1.3 Scope of Guidelines The Guidelines apply to intersections with approach speeds of 45 mph or greater. Stop- controlled, yield-controlled, and uncontrolled approaches to signalized and unsignalized inter- sections are addressed. Because speeds tend to be lower in urban areas, the Guidelines primarily 3 S E C T I O N 1 Introduction

apply to suburban and rural roadways. Speeds on roadway segments outside the influence area of an intersection are not addressed; however, the relationship between segment speed and speed within the intersection influence area is addressed. Although this document focuses on public roadway intersections, many principles also apply to private driveways that include public road- way-like features. Intersections are discrete features of roadway or corridor segments. They frequently occur in urban conditions, but are found more sporadically in rural and suburban areas. Some of the visual cues, physical features, and perceptible qualities that influence operating speeds on road- way segments are different from those that influence operating speed at intersections. The Guidelines focus on speed reduction treatments within an intersection’s geometric and operational influence areas and do not specifically address speed reduction in roadway segments. It is necessary to define the influence area of an intersection to differentiate between reducing speeds on the segment rather than the intersection. The influence area of an intersection includes the area within which the typical section of the roadway segment is modified and that is influ- enced by traffic operations (i.e., queuing and deceleration) related to the intersection. This is shown schematically in Exhibit 1-1. 1.4 Report Organization 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 con- sidering and implementing speed reduction treatments on intersection approaches. Section 4 describes 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. 4 Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections Exhibit 1-1. Roadway segment and intersection area.

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TRB's National Cooperative Highway Research Program (NCHRP) Report 613: Guidelines for Selection of Speed Reduction Treatments at High-Speed Intersections explores the effectiveness of geometric design features as well as signage and pavement markings to reduce vehicle speeds at high-speed intersections. A final report documenting the entire research effort is available online as NCHRP Web-Only Document 124.

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