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Dive into the research topics where Ludovic Leclercq is active.

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Featured researches published by Ludovic Leclercq.


Philosophical Transactions of the Royal Society A | 2010

A mechanism to describe the formation and propagation of stop-and-go waves in congested freeway traffic

Jorge A. Laval; Ludovic Leclercq

This paper introduces a parsimonious theory for congested freeway traffic that describes the spontaneous appearance of oscillations and their ensuing transformation into stop-and-go waves. Based upon the analysis of detailed vehicle-trajectory data, we conclude that timid and aggressive driver behaviours are the cause for this transformation. We find that stop-and-go waves arise independently of the details of these behaviours. Analytical and simulation results are presented.


IEEE Transactions on Intelligent Transportation Systems | 2009

Fundamental Diagram Estimation Through Passing Rate Measurements in Congestion

Nicolas Chiabaut; Christine Buisson; Ludovic Leclercq

Classically, fundamental diagrams are estimated from aggregated data at a specific location. Such a measurement method may lead to inconsistency, which mainly explains the current controversy about their shape. This paper proposes a new estimation method based on passing rate measurements along moving observer paths. Under specific assumptions, it can be proved that in congestion, the passing rate is independent of the traffic flow states. This property allows 1) proof that a linear fundamental diagram is suitable to represent traffic flow behavior involved in the next generation simulation (NGSim) data set and 2) fitting of its two parameters, i.e., the congested wave speed and the jam density.


Transportation Research Record | 2004

MOVING BOTTLENECKS IN LIGHTHILL-WHITHAM-RICHARDS MODEL: A UNIFIED THEORY

Ludovic Leclercq; Stéphane Chanut; Jean-Baptiste Lesort

A unified general framework for the moving-bottleneck models based on the Lighthill-Whitham-Richards theory is proposed. It is shown that all existing models may be considered as particular cases of the general model, differing only by the phenomenology involved, that is, by the shape of the flow-density relationship used for the restricted section. Possible generalization of the model through various flow-density relationships is discussed, as well as the possibilities of experimental validation.


INTERNATIONAL SYMPOSIUM ON TRANSPORTATION AND TRAFFIC THEORY, 15TH, 2002, ADELAIDE, SOUTH AUSTRALIA | 2002

A traffic Flow Model for Urban Traffic Analysis: Extensions of the LWR Model for Urban and Environmental Applications

Florence Giorgi; Ludovic Leclercq; Jean-Baptiste Lesort

The aim of this paper is to propose extensions to the L WR model in order to improve its capacity to fit with urban and environmental applications. Inclusion of public transport vehicles and vehicles kinematics during transitional stages (acceleration and deceleration) are studied in a continuous way using moving boundary conditions concept. The problems raised by the numerical resolution are then analysed. Eventually, urban and environmental applications of such an extended model are presented as well as first results.


Transportation Research Record | 2012

Road Capacity and Travel Times with Bus Lanes and Intermittent Priority Activation

Nicolas Chiabaut; Xiaoyan Xie; Ludovic Leclercq

This study is focused on capacity and travel times in a signalized corridor and bus lanes with intermittent priority (BLIPs). These strategies consist of opening the bus lane to general traffic intermittently when a bus is not using it. Although the benefits of such strategies have been pointed out in the literature, the activation phase has received little attention. In an attempt to fill this gap, the activation of BLIP strategies was studied analytically. To this end, the extended kinematic wave model with bounded acceleration was chosen. BLIP activation reduced capacity and increased the travel time of buses. However, even if this strategy seems to be counterproductive at first, it clearly increases the performance of transit buses on a larger scale.


Transportmetrica B-Transport Dynamics | 2014

Performance analysis for different designs of a multimodal urban arterial

Nicolas Chiabaut; Xiaoyan Xie; Ludovic Leclercq

This article aims to introduce an analysis framework to assess and compare different designs of an urban multimodal arterial before their implementation. Especially, the work focuses on dedicated bus lanes and intermittent bus lanes (IBLs), which are compared to the reference case where the buses and cars are mixed in the same flow. First, analytical considerations highlight the influence of buses and IBLs on traffic dynamics in free-flow conditions. Second, the article resorts to an aggregated and parsimonious model to account for both free-flow and congested traffic states. Such a model provides a better understanding and valuable insights on multimodal traffic dynamics on the arterial. To this end, the concept of passenger fundamental diagram is introduced. With this new relationship, efficiency of the global transport system, i.e. behaviours of cars and buses, is assessed and domains of applications of the different transit strategies are identified.


Transportation Research Record | 2005

Calibration of Flow–Density Relationships on Urban Streets

Ludovic Leclercq

The aim of this paper is to gather some observations resulting from the study of traffic data in an urban environment (Toulouse, France) rather than on freeways, as is often the case in papers that deal with flow-density relationship calibration. Methods developed for freeway data are studied and new ones are presented to address the specificity of traffic behavior in urban areas. A two-step approach is proposed. First, the data are processed to obtain consistent observations for simulation use. This pro cessing includes the calculation of density from occupancy and space mean speed and the aggregation and the selection of data to make them suitable for equilibrium traffic state representation. Then, a best-fit curve is applied to the selected data to obtain flow-density relationships. Finally, the resulting relationships are studied to highlight the peculiarities of traffic behavior in urban streets.


Transportation Research Record | 2011

Wave Velocity Estimation Through Automatic Analysis of Cumulative Vehicle Count Curves

Nicolas Chiabaut; Ludovic Leclercq

A fundamental diagram of traffic flow (and thus wave velocity) under congested traffic conditions is estimated from cumulative vehicle count curves. A new method estimates jam density and congested wave velocity simultaneously on a macroscopic scale. Based on kinematic wave model properties, this method overcomes the drawbacks of existing estimation processes. The objective is to determine the optimal parameters of the kinematic wave model on field data by focusing on wave propagation. The proposed method is used to automatically estimate parameters of the fundamental diagram for the study site. The fundamental diagram is linear in its congested part at the macroscopic scale. A sensitivity analysis is performed to observe the impact of observation days and loop detector locations on wave velocity under congested traffic conditions.


Transportation Research Record | 2014

Clustering Approach for Assessing the Travel Time Variability of Arterials

Etienne Hans; Nicolas Chiabaut; Ludovic Leclercq

Travel time variability may significantly influence a drivers route choice. Urban infrastructure managers are interested in reliable estimation of travel time, which could provide better information to drivers, encourage reassignment on the network, and optimize use of the network. This study addresses arterials in undersaturated conditions with known fixed-time traffic signals. The kinematic wave model was chosen to represent traffic dynamics simply. A semianalytical (grid-free) method is applied to determine the separation between vehicle groups at each signal of the arterial. The main contribution of this paper is an aggregated diagram that describes the functioning of this arterial. The aggregated diagram graphically provides a direct assessment of vehicle travel times with respect to their departure and traffic flow. This tool depends only on signal settings and is cyclic and invariant for fixed-time signals. The diagram can be used to generate probabilistic travel time distributions when some input parameters are uncertain. The diagram appears to offer insight when traffic flow is not accurately known.


Acta Acustica United With Acustica | 2010

Dynamic Traffic Modeling for Noise Impact Assessment of Traffic Strategies

A. Can; E. Chevallier; M. Nadji; Ludovic Leclercq

This paper compares static and dynamic traffic representations to assess noise impact of three traffic strategies on an urban main street: (i) introduction of a bus line, (ii) implementation of a green wave, (iii) replacement of a traffic signal by a roundabout. The dynamic noise prediction model is the only one that can capture changes in noise environment due to those strategies, since it explicitly considers interactions between vehicles on the network. Noise impact of the three strategies is compared through the estimation of statistical descriptors (L 1 , L 10 , L 50 and L 90 ) and the minimum and maximum levels reached per cycle. Within the hypothesis of the study, it is shown that noise levels increase due to buses or speed increase whereas they decrease when a signalized intersection is replaced by a roundabout.

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Jorge A. Laval

Georgia Institute of Technology

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