Demande de transport de personnes: une théorie unifiée de l'urbain à l'intercontinental Seconde partie: population de l'ensemble des voyages réalisés

This paper proposes a theory which links some of the characteristics of trips made by individuals to the travel price and time provided by transport supply, with reference to the socio-economic context. This model appears to be able to reproduce the phenomena that are observed when there is a change in the supply or context on a given origin-destination link. However, above all, the same model can also reproduce those phenomena (changes in urban development aside) which are different in an urban and an interurban context: greater personal mobility, shorter period away from home, lower value of time among travellers, different modal split for trips, slower increase in the number of trips as a result of the socio-economic context, etc. The first part of the paper shows how each of an individual's potential journeys may be characterized by wishes concerning different aspects of the journey and how the different alternatives for the journey in a given context of transport and accommodation supply can be assessed with reference to the gap between wishes and real characteristics. The second part shows how it is possible to determine the total population of journeys made, with reference to both the context and supply. The theory has been illustrated by numerical results obtained for a variety of situations which are representative of urban and interurban areas.     

VirMaLab — atelier virtuel de maintenance: un outil d’aide à la décision pour l’optimisation des politiques de maintenance

This article deals with a generic approach called VirMaLab (virtual maintenance laboratory) for reliabilitybased maintenance modeling for complex systems (with multi-components and multi-states). Based on the probabilistic graphical models formalism (also known as Bayesian networks), this stochastic approach takes into account both the degradation process of the considered system (an original semi-Markovian model is proposed) and maintenance strategies (from diagnosis factors to all kinds of maintenance actions). For complete decision support tools, cost parameters should also be considered (maintenance actions, unavailability of the system, running, etc.). In this article, two applications of this approach to rail maintenance are introduced. The first one focuses on the optimization of the compromise refurbishment/repairing of central part of the RER A line. The second one focuses on the comparison and evaluation of various maintenance strategies in the modernization of the command control systems of Paris metro lines.     

Analyse des pratiques d'accompagnement des enfants et de leurs conséquences

It is more and more common to escort children, and adolescents in rural areas, to school, to see friends, to leisure activities, to the doctor's etc. Some elderly persons are also systematically escorted to activities. These escorting trips are mainly by car, with the mother (or the daughter) driving. Whether children are escorted or not varies according to their age, but the practice has becoming increasingly prevalent in Europe since the 1970s. In England children are allowed to travel unescorted average two and a half years later in 1990 than was the case in 1970 and in the same period the percentage of trips which are escorted has increased by a factor of three and a half. Road safety problems and general insecurity in the area where they live lead parents to escort their children. Most trips of this type are by car. The same situation applies in the former East Germany where many households have only recently acquired a car and where traffic is perceived as dangerous. Although this type of organization of daily family life provides short term opportunities, it nevertheless has long term negative impacts on the acquisition of travel independence by children and adolescents.     

Les valeurs du temps des automobilistes à Marseille en 1995

Eighteen months after the urban tolled underground motorway Prado-Carénage tunnel was-opened in Marseilles (France), road-side interviews were conducted at both the tunnel entry and on the alternative roads. These Revealed Preference data provide a basis for an analysis of competition between a toll road and alternative free roads. In this paper, the binary choice fast toll road vs. free slow road is modelled with respect to the difference in travel time The model is a binary,logit model with a varying Value of-Time (VoT). Estimation by the Maximum Likelihood method shows a significant dispersion of the VoT, with a mean which is 30% higher than the median; it also shows that for a given travel time difference the dispersion in the VoTs explains two thirds of the variability in the path choice. Assuming that the competing roads only differ in price and time, a resulting mean VoT of 70 F/h (12 $/h) was estimated for a car driver during an urban trip in Marseilles in 1995. The first part of the paper introduces the behavioural assumptions in the microeconomic model. Then the data is analyzed and a log-normal distribution of the VoT is estimated. Lastly we indicate how to transfer the method and results to other studies.     

Évaluation des potentiels de réduction des trafics automobiles dans le cas de la zone dense francilienne

The Pari 21 research project does not attempt to justify a move towards a radically different system—practically everything there is to say about the benefits and disadvantages of cars in cities has already been said. Instead, the project will perform simulations and assess, from the point of view of individuals, the feasibility of a transport system that is based mainly On the use of modes Other than the private car in the densely populated zone Of the Greater Paris Area (Paris city plus the inner suburbs). By constructing and evaluating transport policy scenarios, this research also aims to measure the potential for reducing car use in highly urbanized zones, particularly that which results from the reduction in journey speeds which are a likely consequence of the policies in question The method is based on repeated iterations of a simulation model which combines the assignment of round trips to modes other than the automobile with reformulations of transport supply. Demand is channelled towards personal modes (walking, cycling), public transport and a combination of personal and public modes. These iterations are based on the 1991-1992 Paris Region comprehensive travel survey which recorded all the round trips by car made in a typical day by the individuals living in the zone (i.e. the sequence of all trips made between each time the individual leaves home and returns home).     

Impact de la tarification,des fréquences et des temps de transfort sur les flux ferroviares dans le Bassin parisien

We have modelled trips on the Paris basin on the basis of the SNCF long-distance surveys. This modelling allows us to test the impact of pricing, journey times and train frequencies on rail travel demand. Three models have been constructed — a generation model (which computes trip production, that is to say the distribution of trips on the basis of the zones in which rail users reside), a geographical distribution model which is used to estimate the distribution of trip production on the basis of origin and destination zone, and lastly a model choice model which computes the proportion of commuting flows which takes place by rail. In this study the generation model has been partially supplied by the surveys. The distribution model takes thetrip production data output from the generation model in order to evaluate the total of rail flow on each O-D pair. This data is then used to calibrate the modal choice model.     

Mesure automatique de variables de trafic par traitement d'images application à la régulation en milieu urbain

Inductive loops are widely used for urban traffic control purposes. However, the data they provide cover too small an area to provide an accurate picture of traffic conditions at an intersection. As a result there is increasing interest in image processing techniques as these can provide more varied and more accurate data about the scene whatever the prevalling traffic, environmental and lighting conditions. This paper describes the queue length and occupancy measurement system which we have developed. We begin by outlining the constraints which are imposed by the market and the system's environment. The architecture of the system and the algorithm it uses has been specified with reference to these constraints. An account is then give of the experiments we have conducted in order to evaluate the performance of the system and an analysis of the results is presented.     

Évaluation des logiciels critiques: application à la méthode B

From the point of view of safety the bottleneck in the operation of computerized systems currently appears to be the software. In order to improve the safety of software an independent assessment of its quality has been advocated for several years. The assessment of safety critical software consists of a technical examination on the basis of a set of criteria by a body which is independent from the designer. These assessment criteria are derived from the standards which are in force, the state of the art and experience. The objective of an assessments to verify that the product meets the specified safety and functionality requirements. In this paper the authors describe a combined approach to the assessment of safety critical software. On the one hand, the process used in order to develop the software is examined, and on the other the quality of the end product (software) is checked. The first part of the paper will present the position of safety critical software in the context of railway standardization as well as the main assessment techniques with particular reference to that used at Inrets. The second part of the paper will deal with the contribution of formal methods such as the B method to the development of safety critical software. The software assessment aspect will pay particular attention to assessment of the product — analysis of the traceability of requirements, integration and validation of safety properties. The paper ends with a brief account of the extraction and interpretation of metrics for a formal development. Finally the criteria used to assess the process are rapidly described. This approach has been used in the framework of an Esprit project known as Cascade (Certification and Assessment of Safety Critical Application Development).     

Fusion de données pour l'estimation des temps de parcours via la théorie de l'évidence

The emergence of new information technologies and the transformation that has occurred in traffic management have both increased drivers' already considerable need for road traffic information. The travel time is one of the forms in which this information is presented, and a number of systems are based on its dissemination. In this context, this indicator is used as a measure of the impedance (or cost) of routes on the network and/or a congestion indicator. This raises the problem of estimating travel times with an acceptable degree of accuracy, which is a particularly difficult task in urban areas as a result of difficultes of a theoretical, technical and methodological nature. Thus, in order to find out the traffic conditions that prevail on an urban road, the traffic sensors that are usually used to measure traffic conditions are ineffective under certain circumstances. New measurement devices (cameras, GPS or cellphone tracking, etc.) mean that other sources of data are increasingly used in order to supplement the information provided by conventional measurement techniques and improve the accuracy of travel) time estimates. As a result, travel time estimation becomes a typical data fusion problem. This study deals with a multisource estimate of journey times and attempts to provide a comprehensive framework for the utilization of multiple data and demonstrate the feasibility of a travel time estimation system based on the fusion of data of several different types. In this case two types of data are involved, data from conventional induction loop sensors (essentially flow and occupancy measurements) and data from probe vehicles. The selected modelling framework is the Dempster-Shafer Evidence Theory, which has the advantage of being able to take account of both the imprecision and uncertainty of the data. The implementation of this methodology has demonstrated that, in each case, better results are achieved with fusion than with methods based on a single source of data and that the quality of the information, as measured by correctly classified rates, improves as the degree of precision required of the estimate is increased.     

Système d'aide à l'étude de la sécurité routière Vers des outils hydribes,ouverts et intelligents

The objective of this paper is to present the results of a survey of the literature on computer-based systems in road safety analysis. This study was motivated by the needs of road safety analysts and the designers of computer-based tools for use in this area. The literature gave examples where the computerization of several road safety functions is either proposed, undergoing development or actually complete. Furthermore, these functions have been associated with different types of technological orientations. However, some problems still remain to be solved in order to obtain reliable systems with accurate and complete data which integrate the expert knowledge which is needed to analyze and evaluate road safety. The proposed solutions are evolving and this survey suggests that tools in this domain should be hybrid, open and intelligent.     

Âge des conducteurs de voiture et accidents de la route: Quel risque pour les seniors ?

Increasing life expectancy and the fact that the baby boomer generation is reaching retirement age are increasing the size of the elderly population. As road users, seniors have quite specific travel behaviours, and this has an impact on accidents. This paper adopts a quantitative approach with a view to showing the specific characteristics of elderly drivers as regards travel, accidents and road risk. Towards this end it surveys a number of previous studies and takes advantage of recent data to update some of the findings of these contain. Some road risk indicators are described, and attention is paid to the methodological bias inherent in the methods employed. Our analysis shows that the presence of seniors on the roads is growing as the proportion, particularly of the women, in this group who are accustomed to driving increases. They nevertheless cover fewer kilometres than other drivers and develop compensatory strategies, for example not driving when conditions are difficult or driving more slowly than other drivers. When they have accidents they tend to be more severe because of their greater vulnerability. They have higher crash involvement at intersections as a result of detection and estimation difficulties in the driving task. The excess crash risk per kilometre driven for seniors that was observed a few years ago is tending to fall, or even disappear, if the low mileage bias is taken into account.     

Une caractérisation de l'émission acoustique des véhicules au cours des déplacements

Traffic noise is usually measured at fixed points whereas in reality vehicles move and generate noise throughout their trip. This paper therefore puts forward a new method of identifying noise emissions which takes account of the trip as a whole. We have made use of the concept of standard kinematic sequences (which are the elements which form all car trips) and have introduced a new acoustic index to characterize the noise emissions of a vehicle during a sequence. We have achieved this by adapting conventional highway acoustic indices to the way sequences are defined and used. We have calculated examples of these indices from acoustic recordings of isolated vehicles on a test track and from standard sequences.     

Demande de transport de personnes: une théorie unifiée de l'urbain à l'intercontinental Première partie: modalités de réalisation d'un voyage potentiel

This paper proposes a theory which links some of the characteristics of trips made by individuals to the travel price and time provided by transport supply, with reference to the socio-economic context. This model appears to be able to reproduce the phenomena that are observed when there is a change in the supply or context on a given origin-destination link. However, above all, the same model can also reproduce those phenomena (changes in urban development aside), which are different in an urban and an interurban context: greater personal mobility, shorter period away from home, lower value of time among travellers, different modal split for trips, slower increase in the number of trips as a result of the socio-economic context, etc. The first part of the paper shows how each of an individuals potential journeys may be characterized by wishes concerning different aspects of the journey and how the different alternatives for the journey in a given context of transport and accommodation supply can be assessed with reference to the gap between wishes and real characteristics. The second part shows how it is possible to determine the total population of journeys made with reference to both the context and supply. The theory has been illustrated by numerical results obtained for a variety of situations which are representative of urban and interurban areas.