La place des modèles de trafic dans les récentes modélisations des impacts environnementaux des transports. Importance de l’explicitation des méthodes et hypothèses

The authors present a recent development in the use of classic travel demand models (TDMs) to environmental impact assessment of transport, far from its initial target. By comparing previous cases found in the literature (Chester, Seoul, Florence, Brisbane and Saint-Etienne) with their present works (Eval-PDU in Nantes), the authors notice that their predecessors tend to be evasive on their use of TDM. Hence, traffic data are little discussed in these works, while their works constitute one of the main stakes in this kind of study. Indeed, the hypotheses for traffic modeling are impacting the next steps of the modeling chain (pollutants emission/dispersion). The importance of this first modeling stage implies that relevant attention has to be brought to their assumptions and input data.     

Experimental and numerical investigations of the flow around an oar blade

This article aims at verifying the capabilities of a Reynolds-Averaged Navier-Stokes Equations (RANSE) solver (ISIS-CFD, developed at the Fluid Mechanics Laboratory of Ecole Centrale de Nantes [LMF]) to accurately compute the flow around an oar blade and to deduce the forces on it and other quantities such as efficiency. This solver is structurally capable of computing the flow around any blade shape for any movement in six degrees of freedom, both when the blade pierces the free surface of the water and when it does not. To attempt a first validation, a computation was performed for a simplified case chosen among those for which experimental results are available at LMF. If results prove satisfactory for a simplified blade shape and for a movement that respects the main characteristics of blade kinematics, then the solver could be used for real oars and more realistic kinematics. First, the experimental setup is considered, and the objectives, methodologies, and procedures are elucidated. The choice of the test case for numerical validation is explained, i.e., a plane rectangular blade with a constant immersion and a specified movement deduced from analogy with tests on propellers. Next, the numerical framework is presented and the Navier-Stokes solver and methods for handling multifluid flows and moving bodies are described. Lastly, numerical results are compared with experimental data, highlighting an encouraging agreement and proving the relevance and the complementarity of both approaches.     

On-road emissions from urban buses with SCR + Urea and EGR + DPF systems using diesel and biodiesel

Due to growing concerns about NO_x and particulate matter (PM) emissions from diesel engines, stricter regulations are being introduced requiring advanced emission control technology. In response the diesel industry has begun testing various emission control technologies and applying them. To assess vehicle renewal policies of bus companies, two exhaust after-treatment technologies are compared: the combination of a diesel particulate filter and an exhaust gas re-circulation system and the combination of a selective catalytic reduction and urea. On-board emission measurements were conducted under real-world driving conditions on a specific bus route in the city of Madrid.     

Nonlinear Dynamics of Vehicle Traction

Summary The purpose of this study is to understand the nonlinear dynamics of longitudinal ground vehicle traction. Specifically, single-wheel models of rubber-tired automobiles under straight-ahead braking and acceleration conditions are investigated in detail. Customarily, the forward vehicle speed and the rotational rate of the tire/wheel are taken as dynamic states. This paper motivates an alternative formulation in which wheel slip, a dimensionless measure of the difference between the vehicle speed and the circumferential speed of the tire relative to the wheel center, replaces the angular velocity of the tire/wheel as a dynamic state. This formulation offers new insight into the dynamic behavior of vehicle traction. The unique features of the modeling approach allow one to capture the full range of dynamic responses of the single-wheel traction models in a relatively simple geometric manner. The models developed here may also be useful for developing and implementing anti-lock brake and traction control control schemes.     

A Versatile Flat Track Tire Testing Machine

Summary A flat track tire testing machine developed by the IMMa group is described. It permits the simulation and study of the dynamic behavior of a great variety of tires under controllable and repetitive highly dynamic realistic working conditions in the laboratory for a diversity of vehicles, from motorcycles to light trucks. The machine incorporates: - a hydraulically operated tire support and loading system with wide operating ranges; - a computer controlled brake system to simulate braking maneuvers with ABS systems; - a complete sensorial system; - a data acquisition and control system continually monitoring and acting on the experimental variables, i.e., tire and belt speed, longitudinal slip, slip and camber angles, tire pressure, tire normal force, etc. As an application example, results are presented that adjust the parameter of the magic formula for a standard 175/70 R14 passenger vehicle tire. Accurate mathematical tire models are recognized as essential for the prediction of vehicle dynamic performances using simulation tools.     

Extended Ground-Hook - New Concept of Semi-Active Control of Truck's Suspension

This paper deals with the novel control concept, so called ground-hook for active and mainly semi-active suspension of vehicles with the ultimate objective to minimize the tyre-road forces and thus the road damage. The basic ground-hook concept is extended to the several variants which enable to decrease criteria of road damage as well as to increase driver's comfort for a broad range of road unevennesses. Parameters of control law are determined by the parameter optimization for generally nonlinear model. The influence and interaction of the damping rate limits and time constants of variable shock absorbers are also taken into account. The influence of implementation of more complicated truck models is also discussed.     

Automated vehicles: exploring possible consequences of government (non)intervention for congestion and accessibility

ABSTRACT

Academic research on automated vehicles (AVs) has to date been dominated by the fields of engineering and computer science. Questions of how this potentially transformative technology should be governed remain under-researched and tend to concentrate on governing the technology’s early development. We respond in this paper by exploring the possible longer-term effect of government (lack of) intervention.

The paper tests the hypothesis that a “laissez-faire” governance approach is likely to produce less desirable outcomes in a scenario of mass uptake of AVs than would a well-planned set of government interventions. This is done using two prominent themes in transport policy – traffic flow and accessibility – in a scenario of high market penetration of Level-5 automated vehicles in capitalist market economies. The evidence used is drawn from a literature review and from the findings of a set of workshops with stakeholders.

We suggest that a laissez-faire approach will lead to an increase in traffic volume as a result of a growing population of “drivers” and a probable increase in kilometres driven per passenger. At the same time, the hoped-for increases in network efficiency commonly claimed are not guaranteed to come about without appropriate government intervention. The likely consequence is an increase in congestion. And, with respect to accessibility, it is likely that the benefits of AVs will be enjoyed by wealthier individuals and that the wider impacts of AV use (including sprawl) may lead to a deterioration in accessibility for those who depend on walking, cycling or collective transport.

We consider the range of possible government intervention in five categories: Planning/land-use; Regulation/policy; Infrastructure/technology; Service provision; and Economic instruments. For each category, we set out a series of interventions that might be used by governments (at city, region or state level) to manage congestion or protect accessibility in the AV scenario described. Many of these (e.g. road pricing) are already part of the policy mix but some (e.g. ban empty running of AVs) would be new. We find that all interventions applicable to the management of traffic flow would also be expected to contribute to the management of accessibility; we define a small number of additional interventions aimed at protecting the accessibility of priority groups.

Our general finding is that the adoption of a package of these interventions could be expected to lead to better performance against generic traffic-flow and accessibility objectives than would a laissez-faire approach, though questions of extent of application remain.

In our conclusions, we contrast laissez-faire with both anticipatory governance and “precautionary” governance and acknowledge the political difficulty associated with acting in the context of uncertainty. We point out that AVs do not represent the first emerging technology to offer both opportunities and risks and challenge governments at all levels to acknowledge the extent of their potential influence and, in particular, to examine methodically the options available to them and the potential consequences of pursuing them.     

A literature review of mobility services: definitions,modelling state-of-the-art,and key considerations for a conceptual modelling framework

ABSTRACT

This paper presents a comprehensive literature review focused on the supply side of mobility services, providing relevant insights at the conceptual, operational, and modelling levels. Definitions are first drawn from the Mobility as a Service paradigm due to its predominance in the literature. This is followed by an assessment of the operational features of a range of mobility services, including carsharing, bikesharing, ridehailing, and demand responsive transit. To conclude the review, the state-of-the-art in modelling approaches for mobility services is reported, at different levels of complexity and integration. Three of the most important findings and arguments from this paper suggest that a high degree of generality exists for operational features of mobility services; that it is essential to make a distinction between Mobility as a Service and a mobility service in isolation; along with the argument that human agency should be carefully considered in modelling efforts, both for user agent and driver agent decision-making processes. Finally, key considerations are proposed for the future development of a conceptual framework for modelling the supply side of mobility services, which would have a generic service provider model as its core component.     

Current publications

Despite the European Union (EU) efforts promoting policies that encourage short sea shipping (SSS) based on its advantages in terms of intermodality and environment, this mode has not yet reached a significant market share compared to land transport. In this paper, we establish a thesis that suggests that funding programs (such as Marco Polo I and II) have not properly offered the right incentives to promote SSS, and aspects such as the key role of port infrastructure and its characteristics, have not been taken into consideration. In a departure from traditional transport cost models, to prove our thesis, we use a theoretical intermodal competition model to compare alternative modes—road transport vs. SSS. We reach the conclusion that the EU needs to focus on ports and transport system efficiency as a whole in order to compete effectively in the freight transport market.