United States Department of Transportation
i
Development and Tech Transfer of an Integrated Robust Traffic State and Parameter Estimation and Adaptive Ramp Metering Control System
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2021-03-01
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[PDF-3.22 MB]
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Abstract:Real-time updating of traffic state and traffic flow parameters is important for effective real-time traffic control. Because of its simplicity, the Cell Transmission Model (CTM) has been widely used as the underlying traffic flow model based on which traffic state estimation algorithms were designed. A prominent feature of CTM is that for any given road cell, CTM switches between two modes: the free-flow mode and the congestion mode. The switching from the free-flow mode to the congested mode, and from the congested mode to the free-flow mode, respectively, occur once the traffic density of the given cell reaches and drops below the critical density, respectively. Consequently, CTM-based observers, including the CTM-KF observer which can only estimate traffic state in real time, and the more advanced CTM-EKF which can jointly estimate traffic state and traffic flow parameters in real time, both switch between two working modes – the free-flow mode and the congested mode. The observer’s decision on switching its working mode for a given cell is made based on comparing the estimated traffic density of that cell against the pre-known, fixed-valued critical density (for the CTM-KF observer), or against the estimated critical density (for the CTM-EKF observer).
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