On IFT-Based Alinea Control For Freeway Traffic On-Ramp Metering

The increase of traffic flow on freeway has become a serious phenomenon, which can lead to congestion, reduce the traffic run efficiency and the run security. Recently, on-ramp metering becomes the most effective control strategy for improving the situation of freeway traffic. It aims at making traffic flow run in the most optimal state by tuning the number of vehicles to be entering the freeway mainline. The PID technology based ALINEA controller has been verified as a intensively applied control method for ramp metering. It is very simple and can be achieve a good control performance.While, there exist two limits on how to select ALINEA controller's parameters. First, when there is no any priori of the controlled system, we usually adopt the trial-by-trial method to select the controller parameters. Clearly, this method is blind in some cases. Second, when the external disturbance becomes very large, we have to retune the controller parameters to adapt this big change.Aiming to solve this two problems analyzed above, an iterative feedback tuning(IFT) method has been introduced into the local ALINEA ramp metering scheme to tune the controller parameters automatically. The main contributions and innovation- s can be summed as follows:(1) A new ALINEA controller is designed for the local ramp metering by incorporating the iterative feedback tuning strategy (IFT-ALINEA). IFT-ALINEA is model-free in nature, and the controller design and the parameters tuning depend on the real-time input and output (I/O) data of the controlled closed-loop system.,The control gain of ALINEA can be tuned iteratively in terms of the optimal performance index. Apparently, the presented method can overcome the blindness in selecting the proper parameter. The simulation results show that the proposed IFT-ALINEA can achieve a better control performance compared with the pure ALINEA method.(2) In the practice, when some section is lack of downstream detector, the downstream occupancy is needed to be detected by the upstream occupancy of actual measurement. So, we also explore the IFT-ALINEA method based on the upstream occupancy. The downstream occupancy can be estimated by the real-time data of upstream occupancy, and then the parameter tuning can be attained by the estimated occupancy iteratively and automatically. As a result, the occupancy of controlled section can converge to the desired value, asymptotically.(3) In some cases, it is so complex to convert the major occupancy into density. So, it is clear we can just regard the traffic flow as the control variableto make the control target more clear and the control problem more simple. Thus, the IFT-ALINEA scheme based on the traffic flow is explored in this work. The parameter can be tuned iteratively and automatically according to real-time data of traffic flow. The simulation results show the valibity of this method and the traffic flow can converge to the desired value well and the traffic speed of the mainline is improve, as a result the traffic congestion may be avoided.