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Characteristics of speed dispersion and its relationship to fundamental traffic flow parameters
Authors:Chih-Lin Chung  Will W Recker
Institution:1. Department of Transportation Management, Tamkang University, No.151, Yingzhuan Road, Tamsui District, New Taipei City 25137, Taiwan (Republic of China)cchung@mail.tku.edu.tw;3. Institute of Transportation Studies, University of California, 4000 Anteater Instruction and Research Building (AIRB), 92697-3600, Irvine, CA, USA
Abstract:Speed dispersion is essential for transportation research but inaccessible to certain sensors that simply record density, mean speed, and/or flow. An alternative is to relate speed dispersion with these available parameters. This paper is compiled from nearly a quarter million observations on an urban freeway and a resulting data-set with two speed dispersion measures and the three fundamental parameters. Data are examined individually by lane and aggregately by direction. The first dispersion measure, coefficient of variation of speed, is found to be exponential with density, negative exponential with mean speed, and two-phase linear to flow. These empirical relationships are proven to be general for a variety of coefficient ranges under the above function forms. The second measure, standard deviation of speed, does not present any simple relationships to the fundamental parameters, and its maximum occurs at around a half to two-thirds of the free flow speed. Speed dispersion may be significantly different by lane.
Keywords:speed dispersion  coefficient of variation of speed  standard deviation of speed  macroscopic traffic flow model
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