No abstract

Abstract-When freeway traffic is dense, shock waves may appear. These shock waves result in longer travel times and in sudden large variations in the speeds of the vehicles, which could lead to unsafe situations. Dynamic speed limits can be used to eliminate or at least to reduce the effects of shock waves. However, coordination of the variable speed limits is necessary in order to prevent the occurrence of new shock waves and/or a negative impact on the traffic flows in other locations. In this paper, we present a model predictive control approach to optimally coordinate variable speed limits for freeway traffic with the aim of suppressing shock waves. First, we optimize continuous valued speed limits, such that the total travel time is minimal. Next, we include a safety constraint that prevents drivers from encountering speed limit drops larger than, e.g., 10 km/h. Furthermore, to get a better correspondence between the computed and applied control signals, we also consider discrete speed limits. We illustrate our approach with a benchmark problem.Index Terms-Coordinated control, model predictive control (MPC), safe speed limits, shock waves, traffic control, variable speed limits.

This paper formulates the problem of real-time estimation of traffic state in freeway networks by means of particle filtering framework. A particle filter (PF) is developed based on a recently proposed speed-extended cell-transmission model of freeway traffic. The freeway is considered as a network of components representing different freeway stretches called segments. The evolution of the traffic in a segment is modelled as a dynamic stochastic system, influenced by states of neighbour segments. Measurements are received only at boundaries between some segments and averaged within possibly irregular time intervals. This limits the measurement update in the PF to only these time instants when a new measurement arrives, with possibly many state updates in between consecutive measurement updates. The PF performance is validated and evaluated using synthetic and real traffic data from a Belgian freeway. An Unscented Kalman filter is also presented. A comparison of the particle filter with the Unscented Kalman filter is performed with respect to accuracy and complexity.

In literature there are several approaches to eliminate shock waves on freeways by means of dynamic speed limits. Most of them incorporate control systems that have a high computational complexity or that contain parameters without direct physical interpretation, which may make the application in real life difficult. Here we present an approach called SPECIALIST that is based on shock wave theory, and that has parameters with clear physical meaning. The clear interpretation of the parameters leads to an intuitive and insightful formulation of the tuning guidelines. One of the most important features related to the parameter tuning is that the stability of the traffic flow can be ensured by selecting a proper maximum density that is allowed to occur in the speedcontrolled area. In addition, other parameters can be tuned for more robust behavior of the algorithm.We first present the theory of shock wave resolution, and next we develop a practical control algorithm based on this theory. A unique feature of the algorithm is that it first judges the solvability of a shock wave and only starts controlling the speed limits if the shock wave is classified as solvable.The algorithm is demonstrated with a simulation example, and it is shown that its performance is similar to existing approaches.

Abstract-When freeway traffic is dense, shock waves may appear. These shock waves result in longer travel times and in sudden large variations in the speeds of the vehicles, which could lead to unsafe situations. Dynamic speed limits can be used to eliminate or at least to reduce the effects of shock waves. However, coordination of the variable speed limits is necessary in order to prevent the occurrence of new shock waves and/or a negative impact on the traffic flows in other locations. In this paper, we present a model predictive control approach to optimally coordinate variable speed limits for freeway traffic with the aim of suppressing shock waves. First, we optimize continuous valued speed limits, such that the total travel time is minimal. Next, we include a safety constraint that prevents drivers from encountering speed limit drops larger than, e.g., 10 km/h. Furthermore, to get a better correspondence between the computed and applied control signals, we also consider discrete speed limits. We illustrate our approach with a benchmark problem.Index Terms-Coordinated control, model predictive control (MPC), safe speed limits, shock waves, traffic control, variable speed limits.

Abstract-We present the real-world test of the SPECIALIST algorithm in which dynamic speed limits were used to resolve shock waves on freeways. The real-world test was performed in the period September 2009-February 2010 on a 14 km long stretch on the Dutch A12 freeway.For the evaluation of the algorithm various performance measures were determined for each activation of the speed limits. The results show that the SPECIALIST algorithm can resolve shock waves in nearly 80% of the cases when the algorithm activated for shock waves. However, in approximately 50% of the activations the algorithm activated for jam types other than shock waves, in which case the effectivity was 40-50%. Due to the tuning the stability of the traffic flow could be significantly improved, and the number of average activations per day was increased from 1.5 to 2.9 activations per day.The SPECIALIST algorithm was not only evaluated for traffic performance, but also for the correctness of the algorithm for real traffic in terms of expected qualitative behavior. Although the general operation of the algorithm is according to the theoretical expectations, some points for further improvements are identified during the test.

No abstract

Abstract-When freeway traffic is dense, shock waves may appear. These shock waves result in longer travel times and in sudden large variations in the speeds of the vehicles, which could lead to unsafe situations. Dynamic speed limits can be used to eliminate or at least to reduce the effects of shock waves. However, coordination of the variable speed limits is necessary in order to prevent the occurrence of new shock waves and/or a negative impact on the traffic flows in other locations. In this paper, we present a model predictive control approach to optimally coordinate variable speed limits for freeway traffic with the aim of suppressing shock waves. First, we optimize continuous valued speed limits, such that the total travel time is minimal. Next, we include a safety constraint that prevents drivers from encountering speed limit drops larger than, e.g., 10 km/h. Furthermore, to get a better correspondence between the computed and applied control signals, we also consider discrete speed limits. We illustrate our approach with a benchmark problem.Index Terms-Coordinated control, model predictive control (MPC), safe speed limits, shock waves, traffic control, variable speed limits.