Integrated control of traffic flow

2018-11-19Highway congestion is detrimental to traffic mobility, safety and the environment. Numbers of studies have been conducted to avoid or relieve highway congestion with different traffic flow control strategies such as Variable Speed Limit (VSL), Ramp Metering (RM) and Lane Change (LC) recommendation and their combinations. While consistent improvement on traffic safety is reported under existing traffic flow control strategies in macroscopic and microscopic simulations, the results are rather controversial when it goes to the improvement on traffic mobility and the environmental impact, especially in microscopic simulations. Some researchers attribute the inconsistencies to the complexity of underlying reasons of the congestion and highly disordered and stochastic behavior at the bottleneck. Therefore, it is necessary to investigate the dynamical behavior of the open-loop traffic flow systems under all possible demand levels as well as initial densities in order to find out the reasons of the chaotic behavior at the bottleneck, and based on which find an integrated traffic flow controller which is able to provide consistent improvement in traffic mobility, safety and the environmental impact under different traffic scenarios. ❧ In this dissertation, we discover that one of the major reasons of the disordered behavior is the forced lane changes at vicinity of the bottleneck. A lane change controller is proposed which provides lane change recommendations to upstream vehicles in order to avoid the capacity drop. Two types of variable speed limit controllers are designed to improve the flow rate at highway bottleneck together with the lane change controller. The combined lane change and feedback linearization variable speed limit controller, which is build on the first order cell transmission model, can analytically guarantee the global exponential convergence to the desired equilibrium point at which maximum possible flow rate is achieved. Then the combined LC and VSL controller is extended to coordinate with ramp metering controllers. The coordinated VSL, RM and LC controller is able to improve system performance, maintain the queue length on ramps and keep the fairness between mainline and on-ramp flows. Microscopic simulations show consistent improvement under different traffic demand and scenarios. The proposed controller is compared to the widely used MPC control strategy. Both macroscopic and microscopic simulations show that the performance and robustness with respect to model parameter errors and measurement noise of our controller is better than that of the MPC controller. Furthermore, we modify the cell transmission model to include the effect of capacity drop and the decreasing discharging flow of the road section and rigorously investigate its stability properties under all possible traffic flow scenarios. The analysis is used to motivate the design of variable speed limit control to overcome capacity drop without lane change control and achieve the maximum possible flow under all feasible traffic situations. We also consider the case where the system disturbance is included and extend the VSL controller by adding the integral action in order to reject the disturbance while avoiding the capacity drop