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Freeway Ramp Metering Based on Cell Transmission Model and Fuzzy Control

Aiming at the nonlinear and time variant characteristics of a ramp control system, a fuzzy control method is applied to freeway ramp metering in this paper. A cell transmission model (CTM) to describe the freeway flow process is firstly established. Based on the model and in conjunction with nonlinear feedback theory, fuzzy control based ramp controllers are then designed. The ramp metering rates are determined by fuzzy control according to density tracking errors and error increments. Triangle curves are used for the membership functions of the fuzzy variables. The rule base including 56 fuzzy rules is also established. Finally, the controllers are simulated in MATLAB software. The results show that this method can achieve a perfect density tracking performance and eliminate traffic congestion. This approach is quite effective to freeway ramp metering.