Perimeter and boundary flow control in multi-reservoir heterogeneous networks

In this paper, we macroscopically describe the traffic dynamics in heterogeneous transportation urban networks by utilizing the Macroscopic Fundamental Diagram (MFD), a widely observed relation between network-wide space-mean flow and density of vehicles. A generic mathematical model for multi-reservoir networks with well-defined MFDs for each reservoir is presented first. Then, two modeling variations lead to two alternative optimal control methodologies for the design of perimeter and boundary flow control strategies that aim at distributing the accumulation in each reservoir as homogeneously as possible, and maintaining the rate of vehicles that are allowed to enter each reservoir around a desired point, while the system's throughput is maximized. Based on the two control methodologies, perimeter and boundary control actions may be computed in real-time through a linear multivariable feedback regulator or a linear multivariable integral feedback regulator. Perimeter control occurs at the periphery of the network while boundary control occurs at the inter-transfers between neighborhood reservoirs. To this end, the heterogeneous network of San Francisco is partitioned into three homogeneous reservoirs and the proposed feedback regulators are compared with a pre-timed signal plan and a single-reservoir perimeter control strategy. Finally, the impact of the perimeter and boundary control actions is demonstrated via simulation by the use of the corresponding MFDs and other performance measures. A key advantage of the proposed approach is that it does not require high computational effort and future demand data if the current state of each reservoir can be observed with loop detector data. (C) 2013 Elsevier Ltd. All rights reserved

A three-dimensional macroscopic fundamental diagram for mixed bi-modal urban networks

Recent research has studied the existence and the properties of a macroscopic fundamental diagram (MFD) for large urban networks. The MFD should not be universally expected as high scatter or hysteresis might appear for some type of networks, like heterogeneous networks or freeways. In this paper, we investigate if aggregated relationships can describe the performance of urban bi-modal networks with buses and cars sharing the same road infrastructure and identify how this performance is influenced by the interactions between modes and the effect of bus stops. Based on simulation data, we develop a three-dimensional vehicle MFD (3D-vMFD) relating the accumulation of cars and buses, and the total circulating vehicle flow in the network. This relation experiences low scatter and can be approximated by an exponential-family function. We also propose a parsimonious model to estimate a three-dimensional passenger MFD (3D-pMFD), which provides a different perspective of the flow characteristics in bi-modal networks, by considering that buses carry more passengers. We also show that a constant Bus-Car Unit (BCU) equivalent value cannot describe the influence of buses in the system as congestion develops. We then integrate a partitioning algorithm to cluster the network into a small number of regions with similar mode composition and level of congestion. Our results show that partitioning unveils important traffic properties of flow heterogeneity in the studied network. Interactions between buses and cars are different in the partitioned regions due to higher density of buses. Building on these results, various traffic management strategies in bi-modal multi-region urban networks can then be integrated, such as redistribution of urban space among different modes, perimeter signal control with preferential treatment of buses and bus priority

A multivariable regulator approach to traffic-responsive network-wide signal control

The paper presents the design approach, the objectives, the development, the advantages, and some application results of the traffic-responsive urban control (TUC) strategy. Based on a store-and-forward modelling of the urban network traffic and using the linear-quadratic regulator theory, the design of TUC leads to a multivariable regulator for traffic-responsive co-ordinated network-wide signal control that is particularly suitable also for saturated traffic conditions. Simulation investigations demonstrate the efficiency of the proposed approach. Results of TUC's first field implementation and evaluation are also presented. Finally, summarising conclusions are drawn and future work is outlined

Investigation of a City-Scale Three-Dimensional Macroscopic Fundamental Diagram for Bi-Modal Urban Traffic

Recent research has demonstrated that the Macroscopic Fundamental Diagram (MFD) is reliable and practical tool for modeling traffic dynamics and network performance in single-mode (cars only) urban road networks. In this paper, we first extend the modeling of the single-mode MFD to a bi-modal (bus and cars) one. Based on simulated data, we develop a three-dimensional MFD (3D-MFD) relating the accumulation of cars and buses, and the total circulating flow in the network. We propose an exponential function to capture the shape of the 3D-MFD, which shows a good fit to the data. We also propose an elegant estimation for passenger car equivalent of buses (PCU), which has a physical meaning and depends on the bi-modal traffic in the network. Moreover, we analyze a 3D-MFD for passenger network flows and derive its analytical function. Finally, we investigate an MFD for networks with dedicated bus lanes and the relationship between the shape of the MFD and the operational characteristics of buses. The output of this paper is an extended 3D-MFD model that can be used to (i) monitor traffic performance and, (ii) develop various traffic management strategies in bi-modal urban road networks, such as redistribution of urban space among different modes, perimeter control, and bus priority strategies

Μια υβριδικη στρατηγικη ελεγχου φωτεινησ σηματοδοτησησ πραγματικου χρονου και η εφαρμοφη τησ στο αστικο οδικο δικτυο των Χανιων, Ελλαδα: A hybrid strategy for real-time traffic signal control and its implementation at the urban road network of Chania, Greece

The recently developed traffic signal control strategy TUC requires availability of a fixed signal plan that is sufficiently efficient in undersaturated traffic conditions. To drop this requirement, the wellknown Webster procedure for fixed signal control derivation at isolated junctions is employed appropriately for real-time operation based on measured flows. It is demonstrated via simulation experiments and field application that: (a) The developed real-time demand- based approach is a viable real-time signal control strategy for undersaturated traffic conditions; (b) it can indeed be used within TUC to drop the requirement for a prespecified fixed signal plan; (c) it may, under certain conditions, contribute to more efficient results compared with the original TUC method.Ο αναδραστικός κανόνας ελέγχου της στρατηγικής ελέγχου φωτεινής σηματοδότησης TUC απαιτεί την διαθεσιμότητα ενός βελτιστοποιημένου σταθερού πλάνου φωτεινής σηματοδότησης το οποίο είναι αρκούντως κατάλληλο σε συνθήκες ακόρεστης κυκλοφορίας. Για την αποφυγή αυτής της απαίτησης, στην εργασία αυτή ο γνωστός κανόνας του Webster, που χρησιμοποιείται επί δεκαετίες από τους συγκοινωνιολόγους για τον σχεδιασμό σταθερών πλάνων φωτεινής σηματοδότησης σε μεμονωμένους κόμβους βάσει μετρήσεων της κυκλοφοριακής ροής, τροποποιείται κατάλληλα ώστε να συνεργάζεται σε πραγματικό χρόνο με την στρατηγική TUC. Αποτέλεσμα αυτής της τροποποίησης είναι μία υβριδική στρατηγική ελέγχου η οποία σε πραγματικό χρόνο ενεργοποιεί είτε τον αναδραστικό κανόνα ελέγχου της στρατηγικής TUC (περίπτωση κορεσμένης κυκλοφορίας) είτε τον τροποποιημένο κανόνα του Webster (περίπτωση ακόρεστης κυκλοφορίας) σε κάθε ελεγχόμενο κόμβο του δικτύου, ανάλογα με τις τρέχουσες τιμές του επιπέδου κυκλοφοριακού κορεσμού στο συγκεκριμένο κόμβο. Δείχνεται μέσω μικροσκοπικής προσομοίωσης (AIMSUN), υλοποίησης στο πεδίο στο αστικό οδικό δίκτυο των Χανίων και σύγκρισης της υβριδικής στρατηγική ελέγχου με το σύστημα TASS της SIEMENS (περίοδος αξιολόγησης στο πεδίο Μάιος-Ιούνιος 2006): (α) ότι η αναπτυχθείσα προσέγγιση είναι μία στρατηγική ελέγχου πραγματικού χρόνου κατάλληλη τόσο σε συνθήκες ακόρεστης κυκλοφορίας όσο και σε συνθήκες κορεσμένης κυκλοφορίας, (β) ότι o κανόνας του Webster μπορεί πράγματι να συνεργασθεί σε πραγματικό χρόνο με την στρατηγική TUC για την άρση της απαίτησης ενός βελτιστοποιημένου σταθερού πλάνου φωτεινής σηματοδότησης, (γ) ότι η υβριδική στρατηγική ελέγχου μπορεί, υπό ορισμένες προϋποθέσεις, να συμβάλει στην επίτευξη καλύτερων αποτελεσμάτων σε σχέση με την αρχική στρατηγική TUC

A rolling-horizon quadratic-programming approach to the signal control problem in large-scale congested urban road networks

The paper investigates the efficiency of a new signal control methodology, which offers a computationally feasible technique for real-time network-wide signal control in large- scale urban traffic networks and is applicable also under congested traffic conditions. In this methodology, the traffic flow process is modeled by use of the so-called store-and-forward modeling paradigm. The overall problem of network-wide signal control is formulated as a constrained Quadratic-Programming problem, that aims at minimizing and balancing the link queues so as to minimize the risk of queue spillback. For the application of the proposed methodology in real time, the corresponding optimization algorithm is embedded in a rolling- horizon (model-predictive) control scheme. The control strategy’s efficiency and real-time feasibility is demonstrated and compared with the Linear-Quadratic approach taken by the signal control strategy TUC via their simulation-based application to the urban network of the city centre of Chania, Greece, under a number of different scenarios

A hybrid strategy for real-time traffic signal control of urban road networks

The recently developed traffic signal control strategy TUC requires availability of a fixed signal plan that is sufficiently efficient in undersaturated traffic conditions. To drop this requirement, the wellknown Webster procedure for fixed signal control derivation at isolated junctions is employed appropriately for real-time operation based on measured flows. It is demonstrated via simulation experiments and field application that: (a) The developed real-time demand-based approach is a viable real-time signal control strategy for undersaturated traffic conditions; (b) it can indeed be used within TUC to drop the requirement for a pre-specified fixed signal plan; (c) it may, under certain conditions, contribute to more efficient results compared with the original TUC method

Application of the urban traffic control strategy TUC at the Kifisias–Attiki Odos roundabout

Το άρθρο αναφέρεται στην εφαρμογή της στρατηγικής ελέγχου φωτεινής σηματοδότησης TUC στο δίκτυο Κηφισίας - Παρ. Αττικής Οδού με στόχο τη διερεύνηση, μέσω μικροσκοπικής προσομοίωσης, της εν δυνάμει βελτίωσης των κυκλοφοριακών συνθηκών του δικτύου συγκριτικά με το τωρινό εφαρμοζόμενο σταθερό πλάνο φωτεινής σηματοδότησης. Επίσης, διερευνάται αν η στρατηγική TUC μπορεί να αντιμετωπίσει το φαινόμενο εισχώρησης της κυκλοφοριακής συμφόρησης (μέσω των εξόδων της Αττικής Οδού) στην κύρια ροή της Αττικής Οδού, γεγονός που παρατηρείται στην πραγματικότητα, κατά τις ώρες αιχμής, με το τωρινό σταθερό πλάνο σηματοδότησης. Σημειώνεται ότι, βάσει των παρουσιαζόμενων αποτελεσμάτων και βελτιώσεων, είναι σε εξέλιξη η εφαρμογή πεδίου της TUC στο εν λόγω δίκτυο.The paper concerns the application of the real-time traffic control strategy TUC at the Kifisias – Attiki Odos network and investigates, by use of microscopic simulation, the potential improvement of the traffic conditions compared to the currently applied fixed signal plan. In particular, the paper investigates whether the control strategy TUC may reduce the phenomenon of queue spillback (of Attiki Odos freeway exits approaching the roundabout) onto the mainstream freeway flow that occurs, during the peak hours, with the current fixed plan. Based on the presented encouraging results and improvements, the field implementation of TUC strategy at the investigated network is now in progress