On the fundamental diagram for freeway traffic: A novel calibration approach for single-regime models |
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Institution: | 1. Griffith School of Engineering, Griffith University, Gold Coast, QLD 4222, Australia;2. Strome College of Business, Old Dominion University, Norfolk, VA 23529, USA;1. IBM T.J. Watson Research Center, P.O. Box 218, Yorktown Heights, NY 10598, United States;2. Department of Civil Engineering, University of Minnesota, 500 Pillsbury Drive S.E., Minneapolis, MN 55455, United States |
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Abstract: | The speed-density or flow-density relationship has been considered as the foundation of traffic flow theory. Existing single-regime models calibrated by the least square method (LSM) could not fit the empirical data consistently well both in light-traffic/free-flow conditions and congested/jam conditions. In this paper, first, we point out that the inaccuracy of single-regime models is not caused solely by their functional forms, but also by the sample selection bias. Second, we apply a weighted least square method (WLSM) that addresses the sample selection bias problem. The calibration results for six well-known single-regime models using the WLSM fit the empirical data reasonably well both in light-traffic/free-flow conditions and congested/jam conditions. Third, we conduct a theoretical investigation that reveals the deficiency associated with the LSM is because the expected value of speed (or a function of it) is nonlinear with regard to the density (or a function of it). |
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Keywords: | Traffic volume Speed Density Fundamental diagram Traffic flow theory |
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