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An optimisation-oriented first-order multi-lane model for motorway traffic

(Transportation Research Board, 2015) Roncoli Claudio; Roncoli Claudio; Papageorgiou Markos; Παπαγεωργιου Μαρκος; Papamichail Ioannis; Παπαμιχαηλ Ιωαννης

Emerging vehicle automation and communication systems (VACS) may contribute to the mitigation of motorway traffic congestion on the basis of appropriate traffic control strategies. Based on appropriate VACS-based actuators, future traffic control may incorporate vehicle speed control and lane-assignment or lane-changing recommendations. To this end, an appropriate traffic flow model is needed, both for control strategy design and as a no-control base case for comparative evaluation studies. In this context, this paper presents a novel first-order multi-lane macroscopic traffic flow model for motorways which is mainly intended for use within a related optimal control problem formulation. The starting point is close to the well-known cell-transmission model (CTM), which is modified and extended to consider additional aspects of the traffic dynamics, such as lane changing and the capacity drop. The model has been derived with a view to combine realistic traffic flow description with a simple (piecewise linear) mathematical form, which can be exploited for efficient optimal control problem formulations. Although the model has been primarily derived for use in future traffic conditions including VACS, it may also be used for conventional traffic flow representation. In fact, the accuracy of the proposed modelling approach is demonstrated through calibration and validation procedures using conventional real data from an urban motorway located in Melbourne, Australia.

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On microscopic modelling of adaptive cruise control systems

(Elsevier, 2014) Ntousakis Ioannis-Antonios; Ντουσακης Ιωαννης-Αντωνιος; Nikolos Ioannis; Νικολος Ιωαννης; Papageorgiou Markos; Παπαγεωργιου Μαρκος

The Adaptive Cruise Control (ACC) system, is one of the emerging vehicle technologies that has already been deployed in the market. Although it was designed mainly to enhance driver comfort and passengers’ safety, it also affects the dynamics of traffic flow. For this reason, a strong research interest in the field of modelling and simulation of ACC-equipped vehicles has been increasingly observed in the last years. In this work, previous modelling efforts reported in the literature are reviewed, and some critical aspects to be considered when designing or simulating such systems are discussed. Moreover, the integration of ACC-equipped vehicle simulation in the commercial traffic simulator Aimsun is described; this is subsequently used to run simulations for different penetration rates of ACC-equipped vehicles, different desired time-gap settings and different networks, to assess their impact on traffic flow characteristics.

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Relaxation approximations to second-order traffic flow models by high-resolution schemes

(American Institute of Physics, 2014) Nikolos Ioannis; Νικολος Ιωαννης; Delis Anargyros; Δελης Αναργυρος; Papageorgiou Markos; Παπαγεωργιου Μαρκος

A relaxation-type approximation of second-order non-equilibrium traffic models, written in conservation or balance law form, is considered. Using the relaxation approximation, the nonlinear equations are transformed to a semi-linear diagonilizable problem with linear characteristic variables and stiff source terms with the attractive feature that neither Riemann solvers nor characteristic decompositions are in need. In particular, it is only necessary to provide the flux and source term functions and an estimate of the characteristic speeds. To discretize the resulting relaxation system, high-resolution reconstructions in space are considered. Emphasis is given on a fifth-order WENO scheme and its performance. The computations reported demonstrate the simplicity and versatility of relaxation schemes as numerical solvers.

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Local ramp metering with distant downstream bottlenecks: a comparative study

(Institute of Electrical and Electronics Engineers, 2014) Wang Yibing; Kan Yuheng; Papageorgiou Markos; Παπαγεωργιου Μαρκος; Papamichail Ioannis; Παπαμιχαηλ Ιωαννης

The well-known feedback ramp metering algorithm ALINEA can be applied for local ramp metering or included as a key component in a coordinated ramp metering system. ALINEA uses real-time occupancy measurements from the ramp flow merging area that may be at most few hundred meters downstream of the metered on-ramp nose. In many practical cases, however, bottlenecks with smaller capacity than the merging area may exist further downstream for various reasons, which suggests using measurements from those further downstream bottlenecks. Recent theoretical and simulation studies indicate that ALINEA may lead to a poorly damped closed-loop behavior in this case, but PI-ALINEA, a suitable Proportional-Integral (PI) extension of ALINEA, can lead to satisfactory control performance. This paper addresses the same local ramp-metering problem in the presence of downstream bottlenecks, with a particular focus on the general capacity of PI-ALINEA with three distinct types of bottleneck that may often be encountered in practice, i.e. (1) an uphill case; (2) a lane-drop case; (3) an un-controlled on-ramp case. Extensive simulation studies are conducted using a macroscopic traffic flow model to demonstrate that the performance of ALINEA indeed deteriorates in each of these bottleneck cases, while significant improvement is obtained using PI-ALINEA in all cases. Moreover, with its control parameters appropriately tuned beforehand, PI-ALINEA is found to be universally applicable, with little fine-tuning required for field applications.

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A feedback-based approach for mainstream traffic flow control of multiple bottlenecks on motorways

(International Federation of Automatic Control, 2014) Iordanidou Georgia-Roumpini; Ιορδανιδου Γεωργια-Ρουμπινη; Papamichail Ioannis; Παπαμιχαηλ Ιωαννης; Roncoli Claudio; Papageorgiou Markos; Παπαγεωργιου Μαρκος

Mainstream traffic flow control (MTFC) enabled via variable speed limits (VSLs) has been investigated in previous studies, utilizing various control strategies. In this paper a new feedback control strategy is proposed for MTFC enabled via VSLs, considering multiple bottleneck locations. Results are evaluated using a validated macroscopic model. The feedback concept is robust and can be immediately implemented in the field as it considers practical and safety constraints.

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Microscopic simulation analysis of mainstream trafﬁc flow control with variable speed limits

(Institute of Electrical and Electronics Engineers, 2013) Müller Eduardo R.; Carlson Rodrigo Castelan; Kraus Werner Jr.; Papageorgiou Markos; Παπαγεωργιου Μαρκος

Mainstream Traffic Flow Control (MTFC) with Variable Speed Limits (VSL) is a freeway traffic control method which aims to maximize throughput by regulating the mainstream flow upstream from a bottleneck. Recent studies in a macroscopic simulator have shown optimal and feedback MTFC potential to improve traffic conditions. In this paper, local feedback MTFC is applied in microscopic simulation for an on-ramp merge bottleneck. Traffic behavior reveals important aspects that had not been previously captured in macroscopic simulation. Mainly, the more realistic VSL application at specific points instead of along an entire freeway section produces a slower traffic response to speed limit changes. In addition, the nonlinear speed limit-flow relation observed in the microscopic model is more pronounced than what was observed at the macroscopic level. After appropriate modifications in the control law significant improvements in traffic conditions were obtained.

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Model predictive control for multi-lane motorways in presence of VACS

(Institute of Electrical and Electronics Engineers, 2014) Roncoli Claudio; Roncoli Claudio; Papamichail Ioannis; Παπαμιχαηλ Ιωαννης; Papageorgiou Markos; Παπαγεωργιου Μαρκος

A widespread use of vehicle automation and communication systems (VACS) is expected in the next years. This may lead to improvements in traffic management because of the augmented possibilities of using VACS both as sensors and as actuators. To achieve this, appropriate studies, developing potential control strategies to exploit the VACS availability, are essential. This paper describes a model predictive control framework that can be used for the integrated and coordinated control of a motorway system, considering that vehicles are equipped with specific VACS. Microscopic simulation testing demonstrates the effectiveness and the computational feasibility of the proposed approach.

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Optimal control for multi-lane motorways in presence of Vehicle Automation and Communication Systems

(International Federation of Automatic Control, 2014) Roncoli Claudio; Papageorgiou Markos; Παπαγεωργιου Μαρκος; Papamichail Ioannis; Παπαμιχαηλ Ιωαννης

The presence and exploitation of Vehicle Automation and Communication Systems (VACS) while defining optimal control strategies in motorway traffic flow control is addressed in this paper. VACS are supposed to act both as sensors (providing information on traffic conditions) and as actuators, allowing the application of ramp metering, variable speed limit control, and lane changing control. A quadratic programming problem is defined on the basis of a novel first-order traffic flow model for multi-lane motorways. An example is presented in order to illustrate the effectiveness of the proposed optimisation problem.

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Motorway flow optimization in presence of vehicle automation and communication systems

(National Technical University of Athens, 2014) Roncoli Claudio; Papamichail Ioannis; Παπαμιχαηλ Ιωαννης; Papageorgiou Markos; Παπαγεωργιου Μαρκος

This paper describes a novel approach for defining optimal strategies in motorway traffic flow control, considering that a portion of vehicles are equipped with vehicle automation and communication systems. An optimisation problem, formulated as a Quadratic Programming (QP) problem, is developed with the purpose of minimising traffic congestion. The proposed problem is based on a first-order macroscopic traffic flow model able to capture the lane changing and the capacity drop phenomena. An application example demonstrates the achievable improvements in terms of the Total Time Spent if the vehicles travelling on the motorway are influenced by the control actions computed as a solution of the optimisation problem.

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Stability investigation for simple PI-controlled traffic systems

(Institute of Electrical and Electronics Engineers, 2014) Karafyllis Iason; Papageorgiou Markos; Παπαγεωργιου Μαρκος

This paper provides sufficient conditions for the Input-to-State Stability property of simple uncertain vehicular-traffic network models under the effect of a PI-regulator. Local stability properties for vehicular-traffic networks under the effect of PI-regulator control are studied as well: the region of attraction of a locally exponentially stable equilibrium point is estimated by means of Lyapunov functions.

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Assessing the impact of a cooperative merging system on highway traffic using a microscopic flow simulator

(American Society of Mechanical Engineers, 2014) Ntousakis Ioannis-Antonios; Ντουσακης Ιωαννης-Αντωνιος; Porfyri Kalliroi; Πορφυρη Καλλιρροη; Nikolos Ioannis; Νικολος Ιωαννης; Papageorgiou Markos; Παπαγεωργιου Μαρκος

Vehicle merging on highways has always been an important aspect, which directly affects the capacity of the highway. Under critical traffic conditions, the merging of main road traffic and on-ramp traffic is known to trigger speed breakdown and congestion. Additionally, merging is one of the most stressful tasks for the driver, since it requires a synchronized set of observations and actions. Consequently, drivers often perform merging maneuvers with low efficiency. Emerging vehicle technologies, such as cooperative adaptive cruise control and/or merging-assistance systems, are expected to enable the so-called “cooperative merging”. The purpose of this work is to propose a cooperative merging system and evaluate its performance and its impact on highway capacity. The modeling and simulation of the proposed methodology is performed within the framework of a microscopic traffic simulator. The proposed model allows for the vehicle-to-infrastructure (V2I) and vehicle-to-vehicle (V2V) communication, which enables the effective handling of the available gaps between vehicles. Different cases are examined through simulations, in order to assess the impact of the system on traffic flow, under various traffic conditions. Useful conclusions are derived from the simulation results, which can form the basis for more complex merging algorithms and/or strategies that adapt to traffic conditions.

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