Combination of traffic-responsive and gating control in urban networks

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Recent findings regarding macroscopic relationships of urban traffic measures such as the Macroscopic or Network Fundamental Diagram (MFD or NFD) have led to the development of novel traffic control strategies that can be applied at a network-wide level. One pertinent example is perimeter flow control (also known as gating or metering), which limits the rate at which vehicles are allowed to enter an urban region. In general, these gating strategies seek to prevent a network from becoming congested and maximize network efficiency/productivity by maintaining an optimal accumulation of vehicles within the network. Several studies have found that NFDs are more well-defined (i.e., have less scatter and show better overall network performance) when adaptive traffic signals are installed that dynamically respond to local traffic conditions. A combined gating and adaptive traffic control scheme can leverage the more reproducible macroscopic traffic patterns achieved with adaptive signals to provide more robust and efficient gating control. The purpose of this paper is to explore the benefits of combining perimeter gating with locally adaptive traffic signals through micro-simulation of the Chania, Greece traffic network. Two adaptive traffic signal strategies are considered with the feedback-based gating strategy: (1) a simple volume-based strategy and (2) a modified version of the SCATS algorithm. The results of the combined gating/adaptive signal control scheme are compared to gating under fixed traffic signals and the implementation of adaptive signals only. Overall, the study finds that travel delays and congestion can be considerably reduced with the combined strategy. This is because the adaptive traffic signals allow the network to achieve higher network productivity while the gating control allows the network to maintain this higher efficiency for a longer period of time than if left uncontrolled. The results are promising for the implementation of perimeter gating strategies in practice