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.