Modeling driver's evasive behavior during safety-critical lane changes:Two-dimensional time-to-collision and deep reinforcement learning

Lane changes are complex driving behaviors and frequently involve safety-critical situations. This study aims to develop a lane-change-related evasive behavior model, which can facilitate the development of safety-aware traffic simulations and predictive collision avoidance systems. Large-scale connected vehicle data from the Safety Pilot Model Deployment (SPMD) program were used for this study. A new surrogate safety measure, two-dimensional time-to-collision (2D-TTC), was proposed to identify the safety-critical situations during lane changes. The validity of 2D-TTC was confirmed by showing a high correlation between the detected conflict risks and the archived crashes. A deep deterministic policy gradient (DDPG) algorithm, which could learn the sequential decision-making process over continuous action spaces, was used to model the evasive behaviors in the identified safety-critical situations. The results showed the superiority of the proposed model in replicating both the longitudinal and lateral evasive behaviors

Ρύθμιση φωτεινής σηματοδότησης αστικού δικτύου σε πραγματικό χρόνο υπό κορεσμένες συνθήκες κυκλοφορίας

In recent decades, mitigating the traffic congestion in urban road networks has been a crucial issue for both the research and the practical operations, which calls for the development and implementation of improved traffic signal control methods and techniques. In particular, the development of efficient and practicable real-time signal control strategies under saturated traffic conditions is a major challenge, as widely used strategies like SCOOT and SCATS are deemed less efficient under saturated traffic conditions. A practical tool, frequently employed against over-saturation of significant or sensitive links, arterials or urban network parts, is gating. The idea is to hold traffic back (via prolonged red phases at traffic signals) upstream of the links to be protected from over-saturation, whereby the level or duration of gating may depend on real-time measurements from the protected links. The method is usually employed in an ad hoc way (based on engineering judgment and manual fine-tuning) regarding the specific gating policy and quantitative details, which may lead to insufficient or unnecessarily strong gating actions. Recently, the reproducible relationship between flow and density occurring at the network level under certain conditions (e.g. homogeneous spatial distribution of the congestion) known as macroscopic or network fundamental diagram (MFD or NFD), has gained increased popularity. Although the NFD notion is still under investigation in various aspects, it can be exploited as a fruitful basis for derivation of urban signal control approaches.In this thesis, the notion of NFD for urban networks is exploited to improve mobility in saturated traffic conditions via application of gating measures, based on an appropriatesimple feedback control structure. Different gating control strategies (i.e. single perimeter gating control by exploiting complete and reduced NFD, multiple-concentric gating control, perimeter traffic control via remote feedback gating) have been proposed and tested on realistic simulation scenarios of two urban networks (i.e. Chania, Greece and San Francisco, USA) successfully. In the investigated examples, feedback gating is demonstrated to lead to substantial improvements of travel delays, network throughput and travel time reliability.Στις τελευταίες δεκαετίες, η ανάγκη μετριασμού της κυκλοφοριακής συμφόρησης στα αστικά οδικά δίκτυα έχει γίνει ένα κρίσιμο θέμα τόσο για την έρευνα όσο και την πρακτική εφαρμογή, το οποίο καλεί για την ανάπτυξη και την εφαρμογή βελτιωμένων μεθόδων και τεχνικών ελέγχου φωτεινής σηματοδότησης. Ειδικότερα, η ανάπτυξη ικανοποιητικών και εφαρμόσιμων στρατηγικών ελέγχου φωτεινής σηματοδότησης σε πραγματικό χρόνο υπό κορεσμένες συνθήκες είναι μια μεγάλη πρόκληση, καθώς ευρέως διαδεδομένες στρατηγικές που χρησιμοποιούνται έως τώρα όπως το SCOOT και το SCATS θεωρούνται λιγότερο αποτελεσματικές υπό κορεσμένες συνθήκες. Ένα πρακτικό εργαλείο, συχνά εφαρμόσιμο κατά του υπερκορεσμού σημαντικών ή ευαίσθητων συνδέσμων, αρτηριών ή περιοχών του αστικού δικτύου, είναι η ελεγχόμενη είσοδος (gating). Η ιδέα είναι να κρατηθεί η κυκλοφορία (μέσω παρατεταμένων κόκκινων φάσεων στους φωτεινούς σηματοδότες) ανάντη των συνδέσμων που πρέπει να προστατευτούν από υπερκορεσμό, ενώ το επίπεδο ή η διάρκεια της ελεγχόμενης εισόδου μπορεί να εξαρτάται από τις μετρήσεις σε πραγματικό χρόνο από τους προστατευόμενους συνδέσμους. Η μέθοδος αυτή εφαρμόζεται συνήθως για εξειδικευμένα και όχι γενικά προβλήματα (με βάση την εμπειρία και πειραματισμούς) ανάλογα με τη συγκεκριμένη πολιτική ελέγχου εισόδου και τις ποσοτικές λεπτομέρειες, τα οποία όμως μπορεί να οδηγήσουν σε ανεπαρκείς ή υπερβολικές δράσεις ελεγχόμενης εισόδου.Πρόσφατα, η αναπαραγόμενη σχέση μεταξύ της ροής και της πυκνότητας ενός δικτύου υπό ορισμένες συνθήκες (π.χ. ομογενής χωρική κατανομή της συμφόρησης) γνωστό ως μακροσκοπικό θεμελιώδες διάγραμμα (MFD) ή θεμελιώδες διάγραμμα του δικτύου (NFD), έχει αποτελέσει αντικείμενο έρευνας. Παρόλο που η έννοια και ιδιότητες του NFD είναιακόμα υπό διερεύνηση ως προς διάφορες πτυχές, το NFD μπορεί να αξιοποιηθεί ως μια γόνιμη βάση για την παραγωγή προσεγγίσεων του ελέγχου φωτεινής σηματοδότησης σε αστικά δίκτυα. Στην παρούσα διατριβή, η έννοια του NFD για αστικά δίκτυα χρησιμοποιείται με σκοπό τη βελτίωση της κινητικότητας σε κορεσμένες κυκλοφοριακές συνθήκες μέσω της εφαρμογής της ελεγχόμενης εισόδου, με βάση μια κατάλληλη απλή δομή ελέγχου ανάδρασης. Διάφορες στρατηγικές ελέγχου εισόδου (όπως έλεγχος εισόδου σε μια περίμετρο αξιοποιώντας πλήρες και μειωμένο NFD, έλεγχος εισόδου πολλαπλών ομόκεντρων περιμέτρων, περιμετρικός έλεγχος εισόδου μέσω απομακρυσμένων πυλών ανάδρασης) προτείνονται και διερευνώνται σε ρεαλιστικά σενάρια προσομοίωσης δύο αστικών δικτύων (Χανιά, Ελλάδα, και Σαν Φρανσίσκο, ΗΠΑ) επιτυχώς. Στα παραδείγματα που μελετήθηκαν, η ελεγχόμενη είσοδος με ανατροφοδότηση οδηγεί σε ουσιαστικές βελτιώσεις στις καθυστερήσεις κατά την διάρκεια του ταξιδίου και αύξηση της συνολικής ροής στο δίκτυο

Real-time urban traffic control under saturated traffic conditions

Περίληψη: Μη διαθέσιμ

Perceived Attributes in Multidimensional Appraisal of Urban Public Transportation

Viewpoints of various interest groups should be addressed in any public service appraisal. Urbanpublic transportation development and services have diverse impacts on users, operators and the community. The impacts can be characterized by a wide range of perspectives including: efficiency, effectiveness, and efficacy, economic, social and environmental dimensions. The objective of the study summarized herein was to shed some light on the perceivedattributes pertinent to the Tehran regular transit service appraisal. The research revealed interesting results regarding the key perceivedattributes and criteria. The surveyed groups showed interesting similarities and differences in their attributes, selections and choices

Stochastic process in railway traffic flow: Models, methods and implications

We model railway traffic dynamics based on microscopic behavior of vehicles, i.e. speed and distance between vehicles. We consider domain dynamics (e.g. signalling system, kinematic equations) and additional components which are modelled as stochastic factors, affecting speed. Those latter model well the trajectories of railway vehicles observed in real life, representing the combined effect of human actions, track variations, resistances, control systems and actions. We propose multiple stochastic process models (i.e. Brownian motion, Ornstein-Uhlenbeck, doublybounded Cox-Ingersoll-Ross, and doubly mean-reverting Langevin equation) which extend the existing traffic flow theory models for cars towards railway traffic and its specific requirements and constraints. To the best of authors’ knowledge, this paper is the first work which considers stochastic components in order to model mathematically realistic railway traffic dynamics in line with the findings in roadway microscopic traffic behaviour modelling. Closed expressions of relevant characteristics for some stochastic process models have been derived. The behavior of the system has been simulated to derive macroscopic performance indicators and later compared with a deterministic model performance as a benchmark. The models can be useful to estimate the benefits introduced by automation in railways, including Automated Train Operation (ATO).ISSN:0968-090

A model predictive perimeter control with real-time partitions

Previous studies through simulation and empirical data have shown that a Network Macroscopic Fundamental Diagram (NMFD) exists and can be used for designing network optimal perimeter control strategies. These control strategies rely on well defined NMFDs, which highly depend on the homogeneity of the traffic condition in the network. However, it is known that traffic dynamics change drastically during the day in different zones in a large-scale network, and different control strategies might lead to heterogeneous traffic distribution across the urban network. One potential direction is re-partitioning the network to maintain the well defined NMFDs. However, re-partitioning the network changes each sub network’s size, such that it makes the well-defined NMFDs unpredictable. This paper provides a model predictive controlbased optimization approach for perimeter control using real-time partitioning to avoid this problem and utilize re-partitioning techniques. Results show that the proposed method can be used in a heterogeneous network to improve control performance by redistributing accumulations via re-partitioning over time. Our results, which are compared to no control and the traditional model predictive control, yield that the proposed method is superior to the others

Transport electrification for sustainable urban networks

Although transportation has long been recognised as one of the critical factors for socio-economic development, it is responsible for many global greenhouse gas emissions and significant pollutants that cause severe health problem, especially in urban areas. Besides, the rapid development of transportation also brings great concern about energy security. To reduce the transportation system's side effects, Electric vehicles (EVs) have emerged as a promising solution toward sustainable transportation due to their positive impact on environmental issues and energy crisis. However, the adoption of EVs is still minimal compared to conventional gasoline vehicles due to the lack of appropriate charging infrastructure. Furthermore, the electrification of transportation may cost a significant amount of money and result in more congestion (i.e., en-route and charging congestion) due to EVs' routing and charging behaviours. Having these concerns in mind, in this study, we focus on answering the questions of where and how to deploy the charging facilities to promote the widespread adoption of EVs and improve the system performance in the presence of EVs. The objective is to minimise the investment cost of charging infrastructure and the en-route and charging congestion by capturing travellers' routeing choice behaviours with stochastic demand and driving range. The problem is first formulated as a bi-level optimisation problem to capture the mutual interaction between planning decision and traffic flow pattern on the network and then solved by a meta-heuristic. Finally, the proposed framework is tested through the numerical test, and some managerial insights into the facility planning and system performance also be provided

Impede Autonomous Vehicles Merging at On-Ramps?

This paper gives an overview over the phenomena on freeways to be expected when connected and autonomous vehicles (CAV) will be introduced into the traffic system. It discusses the physics of the phenomenon, together with the modelling and simulation approaches that have been described so far. This is followed by an analysis of single vehicle data from a freeway in Lyon to illustrate current speed and headway distributions which are most likely to change with the introduction of CAV’s. Finally, some microscopic simulation results are presented which show that traffic flow typically gains from the introduction of CAV’s, but may also display negative consequences under certain circumstances. More specifically, the traffic characteristics at the merging area in presence of CAV as been studied. It remains for future work to map out precisely where the introduction of CAV’s improves things, and where amendments have to be made to prevent negative side-effects