Nikolaos Geroliminis

Empirical Observations of Congestion Propagation and Dynamic Partitioning with Probe Data for Large-Scale Systems

Research on congestion propagation in large urban networks has been based mainly on microsimulations of link-level traffic dynamics. However, both the unpredictability of travel behavior and the complexity of accurate physical modeling present challenges, and simulation results may be time-consuming and unrealistic. This paper explores empirical data from large-scale urban networks to identify hidden information in the process of congestion formation. Specifically, the spatiotemporal relation of congested links is studied, congestion propagation is observed from a macroscopic perspective, and critical congestion regimes are identified to aid in the design of peripheral control strategies. To achieve these goals, the maximum connected component of congested links is used to capture congestion propagation in the city. A data set of 20,000 taxis with global positioning system (GPS) data from Shenzhen, China, is used. Empirical macroscopic fundamental diagrams of congested regions observed during propagation are presented, and the critical congestion regimes are quantified. The findings show that the proposed methodology can effectively distinguish congestion pockets from the rest of the network and efficiently track congestion evolution in linear time 0(n).

Robust control of bi-modal multi-region urban networks: An LMI optimisation approach

This work concerns the integration of a Three-Dimensional Macroscopic Fundamental Diagram (3D-MFD) modelling for mixed bi-modal traffic (consisting of cars and buses sharing the same infrastructure) in a control framework for congested urban regions. The 3D-MFD relates the accumulation of cars and buses and the outflow (or circulating flow) in a traffic network. A Linear Parameter Varying (LPV) model with uncertain parameters for vehicle composition approximates the original nonlinear system of aggregated dynamics when it is near the equilibrium point for single- and multiple-region cities governed by 3D-MFDs. This model aims at designing a Proportional-Integral (PI) perimeter flow controller that guarantees robust regulation and stability, given that vehicle composition is a slow time-varying parameter. The control gain of the PI regulator is calculated off-line using Linear Matrix Inequality (LMI) optimisation. A simulation-based comparison of the proposed PI control with a pre-timed control plan for an area of San Francisco is carried out. Results show significant improvements in terms of travel delays for cars and buses and schedule reliability of bus services.

A link partitioning approach for real-time control of queue spillbacks on congested arterials

ABSTRACT In oversaturated urban traffic conditions when traffic demand exceeds capacity at signalised intersections, queues fail to clear during the allocated green times. Once a queue reaches the upstream intersection in an arterial, a queue spillback occurs that reduces the upstream link capacity. To mitigate the negative impacts of spillbacks, this article introduces a real-time adaptive traffic signal control method for global management of spillbacks along signalised arterials. The key idea of the proposed method is to implement a real-time partitioning of the arterial to detect critical cluster(s) of consecutive links with oversaturated traffic conditions. The partitioning approach enables to develop locally smaller-sized decentralised signal control strategies operating on the most upstream and downstream intersections of each cluster. Micro-simulation investigations on a real-world arterial site demonstrate the benefits of the proposed approach compared to an existing pre-timed signal control strategy and a classical decentralised green extension strategy. Utilising an advanced queue length detection method and specific focus on queue spillbacks prevention, the control strategy leads to significant reduction of congestion, and arterial total delay.

On the Consistency of Freeway Macroscopic Merging Models

Many first-order macroscopic models for freeway traffic have been developed since the seminal work on the well-known Lighthill–Whitham–Richards, or LWR, continuous model. The asymmetric cell transmission model (ACTM) is a widely accepted macroscopic model integrated into a variety of freeway traffic control frameworks. The model is based on the original cell transmission model; modified merge equations make it computationally tractable for optimization of ramp metering. However, when the common simplistic calibration of the model is used, an infeasible merging behavior is observed at uncontrolled merges, and the resulting queue lengths are not accurately estimated. This paper proposes an elegant analytical relationship, based on traffic flow theory, for calibrating the two parameters involved in the ACTM merge model. The method ensures the physical consistency of the dynamics involved in queue processes in the proximity of a noncontrolled merge junction. This method should be an essential feature of any freeway traffic model.

Model predictive control of large-scale urban networks via perimeter control and route guidance actuation

We design model predictive control (MPC) schemes to improve urban mobility in heterogeneously congested large-scale traffic networks, the modeling and control of which remains a challenge. The multi-region urban network is modeled using the macroscopic fundamental diagram (MFD) of urban traffic, with each region having a well-defined MFD. For more realistic simulations of urban networks with route guidance actuation based control, we propose a new model with cyclic behavior prohibition. Furthermore, we extend upon earlier work on perimeter control based MPC schemes with MFD modeling by integrating route guidance type actuation, which distributes flows exiting a region over its neighboring regions. Performance of the proposed schemes are evaluated via simulations of a congested scenario with noise in demand estimation and measurement errors. Results show the possibility of substantial improvements in urban network performance.