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.     

Modelling and handling dynamics of a wind-driven vehicle

This paper presents a study on the dynamic modelling of a land-yacht, i.e. a ground vehicle that is propelled by wind energy through the use of a vertical airfoil. First, a non-linear dynamic model of the land-yacht motion is derived using a compact matrix notation. Then, an introduction to the study of the performance and handling characteristics is presented. It is considered the vehicle response to input commands, i.e. steering to follow the desired course and adjusting the sail angle according to environmental conditions, that is, wind intensity and direction. The model demonstrates the performance in terms of maximum longitudinal speed and the effects on handling behaviour of the major vehicle design and operational parameters, including location of the centre of gravity and centre of effort, and forward speed, and it leads to conclusions of practical significance concerning directional control and stability.     

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.     

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.     

Electro-hydraulic braking system for autonomous vehicles

Reducing the number of traffic accidents is a declared target of most governments. Since dependence on driver reaction is the main cause of road accidents, it would be advisable to replace the human factor in some driving-related tasks with automated solutions. To automate a vehicle, it is necessary to control the actuators of a car, i.e., the steering wheel, accelerator, and brake. This paper presents the design and implementation of an electro-hydraulic braking system consisting of a pump and various valves, allowing the control computer to stop the car. It is assembled in conjunction with the original circuit for the sake of robustness and to permit the two systems to halt the car independently. This system was developed for installation in a commercial Citroën C3 Pluriel of the AUTOPIA program. Various tests were carried out to verify its correct operation, and an experiment showing the integration of the system into the longitudinal control of the car is described.     

Optimal design and benefits of a short turning strategy for a bus corridor

We develop a short turning model using demand information from station to station within a single bus line-single period setting, aimed at increasing the service frequency on the more loaded sections to deal with spatial concentration of demand considering both operators’ and users’ costs. We find analytical expressions for optimal values of the design variables, namely frequencies (inside and outside the short cycle), capacity of vehicles and the position of the short turn limit stations. These expressions are used to analyze the influence of different parameters in the final solution. The design variables and the corresponding cost components for operators and users (waiting and in-vehicle times) are compared against an optimized normal operation scheme (single frequency). Applications on actual transit corridors exhibiting different demand profiles are conducted, calculating the optimal values for the design variables and the resulting benefits for each case. Results show the typical demand configurations that are better served using a short turn strategy.     

Biologie, transport, complexité

As a result of some of the analogies between biology and transport, including the concepts of evolution and selection, we are wondering whether some ideas and methods used in biology may not be used to provide research avenues within the field of transportation. We are interested in the idea of complexity, which is common to the two scientific fields, but not treated in the same way by either of the two disciplines. By observing the way in which systemic biology has developed, from a largely “data-driven” approach to research guided by data, we are questioning whether such a direction would be possible in the field of transportation. This investigation also leads us to ask questions about “modules”, or the boundaries of the subsystems studied in the field of transportation, through the observation that molecular biology defines these boundaries in terms of the function of the subsystems. In conclusion, we are expressing the notion that these comparisons will lead to new research avenues in the field of transportation.     

Seasonal phytoplankton responses to environmental factors in a shallow Mediterranean lagoon

Phytoplankton community structure was investigated in a 1-year study period from January to December 2006 in the Tunis North Lagoon (South Mediterranean). Twice a month, sampling was carried out from the whole water column. Phytoplankton species composition showed seasonal dynamics following the general environmental variable trends in the study area, with variation in species abundance levels within each season characterised by the presence of different phytoplankton communities. Analysis of environmental variables indicated that phytoplankton-dominant communities were associated with various water physicochemical characteristics, especially water temperature and salinity. Accordingly, significant correlation was recorded between water temperature and dinoflagellates (r = 0.35; p < 0.05) in summer and diatoms (r = 0.69; p < 0.05) in autumn, whereas euglenophytes, cyanophytes and chlorophytes were slightly correlated with temperature in autumn. Salinity was positively correlated with dichtyophytes (r = 0.41; p < 0.05) in winter and with diatoms (r = 0.65; p < 0.05) and euglenophytes (r = 0.57; p < 0.05) in autumn. On the other hand, relationships between high nitrogen nutrient concentration and phytoplankton concentration were recorded for diatoms (r = 0.43; p < 0.05 with NO₂; r = 0.49; p < 0.05 with NO₃) in winter. Silicate concentration supported proliferation of diatoms (r = 0.58; p < 0.05) in autumn in our study period. In contrast, increase of dinoflagellate concentration was associated with the decrease of these parameters in spring and summer.