Discretised link travel time models based on cumulative flows: Formulations and properties |
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Authors: | Jiancheng Long Ziyou Gao WY Szeto |
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Institution: | a School of Economics and Management, Beijing University of Aeronautics and Astronautics, Beijing 100191, China b School of Traffic and Transportation, Beijing Jiaotong University, Beijing 100044, China c Department of Civil Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China |
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Abstract: | In the research area of dynamic traffic assignment, link travel times can be derived from link cumulative inflow and outflow curves which are generated by dynamic network loading. In this paper, the profiles of cumulative flows are piecewise linearized. Both the step function (SF) and linear interpolation (LI) are used to approximate cumulative flows over time. New formulations of the SF-type and LI-type link travel time models are developed. We prove that these two types of link travel time models ensure first-in-first-out (FIFO) and continuity of travel times with respect to flows, and have other desirable properties. Since the LI-type link travel time model does not satisfy the causality property, a modified LI-type (MLI-type) link travel time model is proposed in this paper. We prove that the MLI-type link travel time model ensures causality, strong FIFO and travel time continuity, and that the MLI-type link travel time function is strictly monotone under the condition that the travel time of each vehicle on a link is greater than the free flow travel time on that link. Numerical examples are set up to illustrate the properties and accuracy of the three models. |
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Keywords: | Link travel time Cumulative flow Piecewise linearization FIFO Causality |
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