231 research outputs found
Macroscopic Traffic Flow Model Calibration Using Different Optimization Algorithms
AbstractThis study tests and compares different optimization algorithms employed for the calibration of a macroscopic traffic flow model. In particular, the deterministic Nelder-Mead algorithm, a stochastic genetic algorithm and the stochastic cross-entropy method are utilized to estimate the parameter values of the METANET model for a particular freeway site, using real traffic data. The resulting models are validated using various traffic data sets and the optimization algorithms are evaluated and compared with respect to the accuracy of the produced models as well as the convergence speed and the required computation time
A Lateral Positioning Strategy for Connected and Automated Vehicles in Lane-free Traffic
An optimal-control based path planning algorithm has been developed recently for Connected and Automated Vehicles (CAVs) driving on a lane-free highway, including vehicle
nudging. That vehicle movement strategy considers, in the lateral direction, a lateral desired speed that had been set to zero in previous works; in other words, vehicles avoid
lateral movement if this is not helpful in achieving some of their goals, e.g. achieving a longitudinal desired speed by overtaking slower vehicles. In this work, a lateral positioning strategy for the vehicles is proposed, aiming to improve the vehicles’ longitudinal speeds and the traffic flow, mainly at intermediate densities, by distributing laterally the vehicles based on their longitudinal desired speeds. The intention is to leverage the existing optimal control formulation to move the CAVs to appropriate lateral positions, while respecting other, higher-priority sub-objectives, such as avoiding crashes. First, the longitudinal desired speed of each vehicle is mapped to a lateral desired position under the premise “faster vehicles drive farther left”. Then, the value of the desired lateral speed is updated in real-time in dependence on the vehicle’s current versus the desired lateral position, letting the optimal control problem, with the given sub-objective priorities, decide on the actual vehicle path. The proposed strategy is demonstrated via traffic simulations, involving various traffic densities, on a ring-road. Several quantities, such as the reached average flows and statistical measures of the error in the lateral position are computed for evaluation and comparison purposes
GLOSA System with Uncertain Green and Red Signal Phases
A discrete-time stochastic optimal control problem was recently proposed to address the GLOSA (Green Light Optimal Speed Advisory) problem in cases where the next signal switching time is decided in real-time and is therefore uncertain in advance. However, there was an assumption that the traffic signal is initially red and turns to green, which means that only half traffic light cycle was considered. In this work, the aforementioned problem is extended considering a full traffic light cycle, consisting of four phases: a certain green phase, during which the vehicle can freely pass; an uncertain green phase, in which there is a probability that the traffic light will extend its duration or turn to red at any time; a certain red phase during which the vehicle cannot pass; and an uncertain red phase, in which there is a probability that the red signal may be extended or turn to green at any time. It is demonstrated, based on preliminary results, that the proposed SDP (Stochastic Dynamic Programming) approach achieves better average performance, in terms of fuel consumption, compared to the IDM (Intelligent Driver Model), which emulates human-driving behavior
A Nonlinear Heat Equation Arising from Automated-Vehicle Traffic Flow Models
In this paper, a new nonlinear heat equation is studied that arises as a
model of the collective behavior of automated vehicles. The properties of the
solutions of this equation are studied by introducing the appropriate notion of
a weak solution that requires certain entropy-like conditions. To obtain an
approximation of the solution of the nonlinear heat equation, a new
conservative first-order finite difference scheme is proposed that respects the
corresponding entropy conditions, and certain links between the weak solution
and the numerical scheme are provided. Finally, a traffic simulation scenario
and a comparison with the Lighthill-Witham-Richards (LWR) model are provided,
illustrating the benefits of the use of automated vehicles.Comment: 36 pages, 9 figure
Controlling Automated Vehicles on Large Lane-free Roundabouts (Extended Version)
Controlling automated vehicles on large lane-free roundabouts is challenging
because of the geometrical complexity and frequent conflicts among entering,
rotating, and exiting vehicles. This paper proposes a comprehensive methodology
to control the vehicles within the roundabout and the connected road branches.
The developed real-time vehicle movement strategy relies on offline-computed
wide overlapping movement corridors, one for each Origin-Destination (OD)
movement, which delineate the admissible movement zones of corresponding OD
vehicles. Also, space-dependent desired orientations are determined by
destination, so as to mitigate potential vehicle conflicts and reduce trip
distance. A distributed (per vehicle) movement control strategy, using two
nonlinear feedback controllers (NLFC), for circular and straight movements,
respectively, is employed to navigate each vehicle within the respective OD
corridor toward its destination, accounting for the desired orientation and
avoiding collisions with other vehicles; while boundary controllers guarantee
that the corridor boundaries will not be violated, and the exit will not be
missed. As an overly complicated case study, we consider the famous roundabout
of Place Charles de Gaulle in Paris, featuring a width of 38 m and comprising a
dozen of bidirectional radial streets, hence a total of 144 ODs. The pertinence
and effectiveness of the presented method is verified via microscopic
simulation and evaluation of macroscopic data.Comment: 16 pages, 21 figures, 1 table, and 47 equations As compared with the
previous version: - Some minor changes in the text - The first simulation is
replaced with a new one to have more clear figure
INTEGRATED TRAFFIC CONTROL FOR FREEWAYS USING VARIABLE SPEED LIMITS AND LANE CHANGE CONTROL ACTIONS
The wide deployment of vehicle automation and communication systems (VACS) in the next decade is expected to influence traffic performance on freeways. Apart from safety and comfort, one of the goals is the alleviation of traffic congestion which is a major and challenging problem for modern societies. The paper investigates the combined use of two feedback control strategies utilizing VACS at different penetration rates, aiming to maximize throughput at bottleneck locations. The first control strategy employs mainstream traffic flow control using appropriate variable speed limits as an actuator. The second control strategy delivers appropriate lane-changing actions to selected connected vehicles using a feedback-feedforward control law. Investigations of the proposed integrated scheme have been conducted using a microscopic simulation model for a hypothetical freeway featuring a lane-drop bottleneck. The results demonstrate significant improvements even for low penetration rates of connected vehicles.
Document type: Articl
An Application of Software Engineering for Reading Linear-B Script
Linear-B script has been studied for sixty years since its decipherment. The laborious efforts of the scholars have revealed many linguistic aspects of the oldest known form of Greek (i.e., Mycenaean/Danaic Greek), thus allowing the study of this Indo-European language and its dynamics for thirty-five centuries. In addition, linguistic phenomena closer to the roots of Indo-European languages can be also studied. Yet, the limited usage of Linear-B script, merely for keeping records, and its incompatibility to the Greek phonotactics causes misinterpretations of various kinds. The study of Linear-B was not supported till recently by interactive software tools that would facilitate both research and training. Especially for Greek speakers, the resources are even more limited. This paper presents the development of an interactive software system for the study, learning and researching of Linear-B by Greek speakers. This software system is also suggested as a model for the interpretation of other archaic languages
- …