Cell Transmission Model Based Variable Speed Limit Control for Freeway

摘要

The use of variable speed limit (VSL) control along freeways in an effort to improve bottlenecktraffic flow is a technique that has been around for some time. In this paper, the authors proposea simple yet very efficient VSL control model using the cell transmission model (CTM). Twomodifications of the fundamental diagram (FD) of the CTM are proposed. The first permits oneto model active bottleneck cell in which there is a capacity drop once feeding flow exceeds itscapacity. The second modification permits variable free flow speeds for the cells operated withVSL control. In order to allow these modifications, the local demand-supply approach is adoptedto change the boundary condition of the CTM, and then the traffic density is predicted in thefreeway cells. Speed dynamics is derived from a piecewise linear FD. As part of the VSL controlalgorithm, the modified CTM is implemented in the freeway corridor Whitemud Drive,Edmonton with the model predictive control (MPC) approach. In order to update the storagecapacity of freeway cells, the authors have developed and implemented a time-space discretequeue estimation model during VSL control. The analysis is carried out in a micro-simulationmodel, VISSIM, within a scenario in which shock waves are present. This simulation studyreveals that, in terms of traffic mobility, VSL is mostly effective during congestion periods.Specifically, for the studied corridor, improvements to Total Travel Time (TTT), Total TravelDistance (TTD), and flow were around 15.0%, 6.0%, and 7.0%, respectively.