Per-Lane Variable Speed Limit and Lane Change Control for Congestion Management at Bottlenecks

The vast majority of Variable Speed Limit (VSL) control strategies developed in the literature are based on the well-known macroscopic Cell Transmission Model (CTM), where the traffic density can vary in the longitudinal direction, but it is assumed to be constant in the lateral direction. That is, all lateral flows between lanes due to lane changes are ignored. This assumption does not accurately reflect the traffic behavior since every lane behaves differently depending mainly on the intensity of lane changes, especially close to bottleneck locations. Treating a multi-lane roadway as a single lane by the VSL controllers may fail to utilize the full motorway capacity when the bottleneck is active. In this paper, every lane is treated as a separate stream using a multi-lane CTM, where the net lane-changing flow is modeled as an additional unknown term in the conservation equation. The unknown net flow is estimated in real-time, and its estimate at each time is used in calculating the VSL command for each lane. Then, a Lane Change (LC) controller is combined with the VSL to prevent creating a queue in the vicinity of the bottleneck. The stability properties of the closed-loop system are analyzed, where the integrated control scheme guarantees that the lane traffic density operates within the free-flow region of the fundamental diagram. Microscopic simulations based on the commercial software PTV Vissim are used to demonstrate the effectiveness of the proposed control scheme.