A Performance-Based Highway Geometric Design Process (2016) / Chapter Skim
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5 Highway engineering and design have evolved over the years in response to many factors, events, knowledge gained from both research and "trial and error," and public policy initiatives. The following is a summary timetable of the evolution of design policy in the U.S.
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6 a performance-Based highway Geometric Design process 2.2 The 1950s -- The Technology of Highway Planning and Design Addresses Burgeoning Mobility Needs and National Public Policy Advances The 1950s saw rapid economic and population growth in the U.S.; Many cities grew significantly. The automobile became the predominant transportation mode.
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the evolution of highway Design in the U.S. 7 2.4 The 1970s -- Environmental Initiatives Drive National Transportation Policy and Programs The 1970s saw the maturation of the Interstate system, an explosion in traffic, and the onset of developing societal problems and issues associated with construction and operation of the highway system.
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8 a performance-Based highway Geometric Design process In response to these trends the 1982 Surface Transportation Act mandated study of resurfacing, restoration, and rehabilitation (3R) projects.
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the evolution of highway Design in the U.S. 9 manner; designers were taught to understand flexibility that did exist within AASHTO policies, and the design process as one of making choices and trade-offs was codified.
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10 a performance-Based highway Geometric Design process In the view of most DOT leaders, funding limitations to meet program needs have become permanent. Part of the solution to this has been emergence of P3s (public/private partnerships)
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the evolution of highway Design in the U.S. 11 the highway agency and community on a level playing field, and considers all trade-offs in decision making.
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12 a performance-Based highway Geometric Design process Highway agency criteria for design of 3R projects on nonfreeway facilities and the AASHTO Guidelines for Geometric Design of Very Low-Volume Local Roads (ADT ≤ 400)
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the evolution of highway Design in the U.S. 13 Context sensitive solutions (CSS)
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14 a performance-Based highway Geometric Design process Highway agencies generally set LOS targets for each project. Table 2, based on the Green Book Table 2-5, suggests specific LOS targets for projects by functional class and terrain.
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the evolution of highway Design in the U.S. 15 CMF1x = Crash modification factors specific to site type x and specific geometric design and traffic control features y; and Cx = Calibration factor to adjust SPF for local conditions for site type x.
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16 a performance-Based highway Geometric Design process A performance-based design process with goals based on safety targets (i.e., specific crash frequencies either for expected total crashes or expected crashes by severity level) is now feasible, although it does not appear that such a process has yet been adopted.
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the evolution of highway Design in the U.S. 17 MoDOT is not the only state DOT faced with many demands -- such as maintenance, expanding infrastructure, and improving safety -- and having to meet these demands with limited financial resources.
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18 a performance-Based highway Geometric Design process • 40 km/h (25 mph) for fixed-object crashes, and • 30 km/h (20 mph)
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the evolution of highway Design in the U.S. 19 Given this approach, VE can be seen as a variation of performance-based design and practical design.
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20 a performance-Based highway Geometric Design process then current state of knowledge on lane width, shoulder width, and shoulder type (Zegeer and Deacon 1987) ; bridge width (Mak 1987)
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the evolution of highway Design in the U.S. 21 With the above in mind, development of the AASHTO VLVLR guidelines presented geometric design criteria for many specific design elements, applicable to new construction or reconstruction projects that are less restrictive, and thus less costly to implement, than the design criteria applicable to higher-volume roads, as presented in the Green Book.
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22 a performance-Based highway Geometric Design process • Performance (operational, safety) is important, • Performance may have many dimensions, • Safety performance should focus on elimination or mitigation of severe crashes, • Speed and crash severity are closely linked, • Existing roads with known problems are different from new roads, • Traditional design approaches are believed by professionals to yield suboptimal results, • Focusing on identifying and addressing the problem(s)
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the evolution of highway Design in the U.S. 23 problem that DOTs undertook with little outside involvement.
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24 a performance-Based highway Geometric Design process remain many criteria that were developed to address the practical issues associated with hand calculations, a need that is long gone. • The direct input of what may be referred to as "external" influences such as environmental effects remains outside the direct application of design criteria to the design process.
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