Capacity Analysis of Interchange Ramp Terminals Final Report (1997) / Chapter Skim
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CHAPTER 1 Introduction and Research Approach
CHAPTER 1 Introduction and Research Approach
Pages 1-6
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Within freeway/arsenal and arterial/arterial interchanges, signalized ramp terminals connecting to the arterial cross street are often the key operational geometric element. Unfortunately, the interchange facility, which is a very costly link in the highway network, often performs poorly, having numerous conflict points, high traffic demands, large changes in speeds required by motorists, and high-volume horning movements often exceeding four times the normal average observed at conventional intersections.
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A wide range of service interchange configurations that include one or more traffic signals at the ramp terminals should be specifically addressed. This statement of scope includes conventional diamonds, compressed diamonds, tight urban diamonds, single-point interchanges, and three partial cloverleafs (parclos)
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A total of 350 returned questionnaires were deemed completely responsive and valid. The first-stage survey results revealed that engineers analyze traffic operations of interchanges quite often, and that most service interchanges are diamonds (either compressed or tight urban)
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In addition, thirty-five interchanges located around the country were suggested as candidate study sites for subsequent model development, testing and validation. 1.3.2 Traffic Models Following a detailed literature review of intersection and interchange capacity models, analysis methods and recent research, the development of a targeted set of traffic models was initiated toward satisfying the specific operational needs identified in the field survey and project objectives.
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In particular, the PDX Model required extensive software coding to get the related complex algrorithms described to perform efficiently for a wide range of traffic conditions. A prototype software design for service interchange database management' named INTERCHANGE' was also developed to demonstrate an efficient database architecture for processing all types of two-level signalized service interchanges for subsequent capacity and operational analyses.
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