The Braess's Paradox in Dynamic Traffic

The Braess's Paradox (BP) is the observation that adding one or more roads to the existing road network will counter-intuitively increase traffic congestion and slow down the overall traffic flow. Previously, the existence of the BP is modeled using the static traffic assignment model, which solves for the user equilibrium subject to network flow conservation to find the equilibrium state and distributes all vehicles instantaneously. Such approach neglects the dynamic nature of real-world traffic, including vehicle behaviors and the interaction between vehicles and the infrastructure. As such, this article proposes a dynamic traffic network model and empirically validates the existence of the BP under dynamic traffic. In particular, we use microsimulation environment to study the impacts of an added path on a 2-by-3 all stop-controlled grid network. We explore how the network flow, vehicle travel time, and network capacity respond, as well as when the BP will occur. We find that adding a path to the network does not increase the overall network output flow and worsens it when the added path is more attractive. We observe that traffic flow on the added path increases first, but decreases after the demand level reaches an inflection point. The added path worsens the average travel time of all vehicles and does not provide additional operational capacity to the network.