Update of Highway Capacity Manual: Merge, Diverge, and Weaving Methodologies (2023) / Chapter Skim
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Pages 107-114
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From page 107... ...
107 Overview This chapter presents the recommended speed and capacity models for merge, diverge, and weaving segments developed through this research along with the recommended value of density at capacity for these segment types and compares the recommended models to the HCM 6th Edition models. The recommended implementation of these models in the HCM, the project's primary deliverable, is presented in four draft HCM chapters.
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From page 108... ...
108 Update of Highway Capacity Manual : Merge, Diverge, and Weaving Methodologies where So = average speed of the weaving segment (mph) , Sb = average speed of an equivalent freeway basic segment (per the HCM)
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From page 109... ...
Conclusions and Suggested Research 109 Recommended Density at Capacity The field data collected by this project revealed that the capacity of freeway weaving, merge, and diverge segments occurs around 35 pc/mi/ln, a value considerably lower than the HCM's current values of 43 pc/mi/ln for weaving segments and 45 pc/mi/ln for merge and diverge segments. In accordance with the fundamental theory of traffic flow, a lower value of density at capacity results in a lower value of segment capacity.
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From page 110... ...
110 Update of Highway Capacity Manual : Merge, Diverge, and Weaving Methodologies where CW = weaving segment capacity (pc/h/ln) ; a, b, c = intermediate calculation parameters; W = weaving segment intensity; B = basic segment term; BP = basic segment breakpoint, from HCM Exhibit 12-6 (pc/h/ln)
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From page 111... ...
Conclusions and Suggested Research 111 where CM = merge segment capacity (pc/h/ln) , A, B, C = intermediate calculation parameters, vR = demand flow rate for ramp movement (pc/h)
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From page 112... ...
112 Update of Highway Capacity Manual : Merge, Diverge, and Weaving Methodologies the HCM 6th Edition models and provides support for why they are recommended to replace the HCM 6th Edition models. • General advantages of the recommended models: – The recommended models are consistent with the fundamental speed–flow–capacity relationship, unlike the HCM 6th Edition models.
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From page 113... ...
Conclusions and Suggested Research 113 • Diverges – The recommended speed model has a better RMSE than the HCM 6th Edition for simple diverges (4.04 mph versus 6.12 mph)
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From page 114... ...
114 Update of Highway Capacity Manual : Merge, Diverge, and Weaving Methodologies different sets of ramps)
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