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1 This report establishes an approach practitioners can use to evaluate the performance tradeoffs of different project development and design decisions. The motivation for integrating performance- based analysis into project development and geometric design decisions is two-fold. 1. Roadway agencies have limited resources to invest and often are developing projects within a physically constrained environment (e.g., limited right-of-way in an urban area, minimizing impacts in environmentally sensitive areas). It is not always fiscally possible or reasonable to categorically construct roadways to meet design standards. Through initiatives such as context- sensitive solutions and practical design, as a profession, we have learned that in many circum- stances we must construct roadways using flexible design approaches to adapt to the unique needs of each contextual design environment. 2. The form of highways, streets, interchanges, and intersections has a direct impact on perfor- mance measures beyond average delay or travel time for an automobile. The form of our streets and highways directly affects peopleâs ability to comfortably travel by foot, bike, and transit. The form can influence safety performance or various users. It can have direct impact on a communityâs ability to attract new employers, manage air quality, meet the needs of lower- income households, and create a feeling of livability and vitality for residents, visitors, and employers. Our highways and streets have many more purposes and can bring great value to communities. Our streets and highways directly influence the quality and substance of how we live. In practice, we encounter projects that are motivated by a desire to reduce crashes, increase com- munity livability, improve air quality, revitalize corridors, and other related desires. Historically, we have sometimes used increased capacity or reduced vehicle delay as the surrogate performance measure to select street and highway design elements. This surrogate was meant to represent the needs of the various roadway users. Increasing capacity or providing flatter and faster designs may reduce vehicle delay through increased speeds. However, this could simply result in a change in the severity of crashes. This report presents an approach for understanding the desired outcomes of a project, selecting performance measures that align with those outcomes, evaluating the impact of alternative geo- metric design decisions on those performance measures, and arriving at solutions that achieve the overall desired project outcomes. Part A (Chapters 1 through 4) of this report presents the body of knowledge that forms the basis for performance-based analysis to inform geometric design decisions. Part B (Chapters 5 and 6) presents applications guidance to incorporate performance- based analysis into project development and geometric design decisions. S U M M A R Y Performance-Based Analysis of Geometric Design of Highways and Streets
