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Traffic flow control on motorways for throughput maximization

Iordanidou Georgia-Roumpini

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Summary

Traffic congestion on motorways is one of the most serious problems of modern societies that leads to a significant reduction in motorway infrastructure capacity. This reduction regularly occurs during peak periods, causing degradation in terms of travel times, traffic safety, fuel consumption, and environmental pollution. So far, several traffic control measures have been proposed to alleviate traffic congestion. However, some of them face limitations; e.g., ramp metering (RM) efficiency is limited by the available storage space at on-ramps, whereas route guidance is most valuable under non-recurrent traffic congestion. Mainstream traffic flow control (MTFC) enabled via variable speed limits (VSLs) has been investigated in previous studies, utilizing various control strategies. In this thesis, an extended feedback control strategy is proposed for MTFC enabled via VSLs, considering multiple-bottleneck locations. The evaluation of the proposed control strategy, using a second order macroscopic traffic flow simulator, and its comparison with an optimal control approach, for a real network, demonstrates its efficiency. The feedback concept is approaching the performance of optimal control, is more robust (no model or demand predictions are needed), and can be immediately implemented in the field as it considers practical and safety constraints.The development and deployment of simple, yet efficient, coordinated and integrated control tools for motorway traffic control remains a challenge. In this thesis, a generic integrated feedback-based motorway traffic flow control concept is proposed. It is based on the combination and suitable extension of control algorithms and tools proposed or deployed in other studies, such as RM or VSL-enabled cascade-feedback mainstream traffic flow control, and allows for consideration of multiple bottlenecks. The new controller enables coordination of RM actions at a series of on-ramps, as well as integration with VSL control actions, towards a common control goal, which is bottleneck throughput maximization. While doing this, the approach considers a pre-specified (desired) balancing of the incurred delays upstream of the employed actuators, via a suitably designed knapsack problem. Despite the multitude of the offered configurations, options and possibilities, the generic control algorithm remains simple, efficient and suitable for field implementation. The control algorithm is demonstrated and evaluated using a validated macroscopic traffic flow model for a real infrastructure and has been compared to other control structures. The integrated controller is shown to be superior as it takes advantage of all the available storage capacity required for queueing upstream of the bottlenecks. The feedback controller is robust as there is no need, neither for any predictions of the demand nor for any model calibration or parameter identification.

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