2 Freeway Ramp Metering Control Made Easy and Efficient (original) (raw)
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2006
Critical density of a freeway link is subject to changes over time due to circumstances such as environmental conditions (snow, rain, etc.), traffic incidents. Because of its impacts on the performance of some ramp metering strategies that make use of critical density as a threshold value for control action, it is necessary to trace the real value of the critical density. Hence, methodologies for the on-line estimation of critical density using Extended Kalman Filtering (EKF) and Kalman Filtering (KF) were proposed in this paper. Basically, critical density was chosen as the state variable to be determined using system output, measurement of traffic flow on the downstream freeway link. Then, these methods are evaluated using microscopic simulation environment, PARAMICS. The results indicate that both methods (using KF and EKF) provide better performance in terms of tracing time-dependent changes of real critical occupancy effectively for all the scenarios tested compared with the ca...
Switched Observer-based Ramp Metering Controllers for Freeway Systems
This paper proposes local ramp metering controllers to be applied in freeways in which there are not sensors measuring the traffic density close to the on-ramps. Since the ramp metering control laws to be applied are based on the value of the traffic densities upstream or downstream the on-ramps and since these densities cannot be measured, the density estimates provided by distributed consensus-based switched observers developed in a previous work are used. In particular, on the basis of the observability properties of the considered freeway system, which is modeled as a piecewise-affine state-dependent system, a switched ramp metering controller based on a distributed observer is proposed. According to the present mode of the freeway system, the local controller of each on-ramp switches between a feedback controller based on the downstream density, a feedforward controller based on the upstream density and a pre-computed control law.