La surestimation de la distance intervéhiculaire dans le brouillard

The difficulties of driving in fog are usually perceived in terms of lower sight distances and reduced ability to anticipate. However, the fall in the quality of visual information can also lead to errors in judgement by affecting the way drivers perceive their environment and their movement within it. We have conducted a series of experiments in a fog chamber and on a driving simulator, with the main aim of investigating the influence of fog on vehicle headway perception. Our results have revealed that distances are seriously overestimated in fog, and that this is likely to contribute to lower headways under such conditions, In fog an overestimation of headway between 20 and 55% was observed when vehicles were visible only as a result of their rear lights, which is the case in night-time or thick daytime fog. Under these conditions, the characteristics of vehicle lights become extremely important. Overestimation of distance becomes greater when vehicles have only one rear light instead of two, and when their two reac lights are close together. Perception of vehicle distance is therefore improved by two rear lights, placed as far apart as possible to indicate the dimensions of the vehicle. No significant overestimation of headways was found during thin or moderate daytime fog, when the vehicle outline remained visible. The results have shown the importance of the familiar size of vehicles as an indicator of distance in the situations we have investigated. They confirm the hypothesis that basic mechanisms of space perception are modified in fog.     

Temps et pratiques modales. Le plus court est-il le mieux ?

This paper considers the rationality of travel practices with regard to journey times. The problem can be formulated as follows: to what extent is modal choice determined by a qualitative rather than a quantitative comparison between journey times? Modal choice for home-to-work trips in the conurbations of Grenoble, Geneva, Lausanne and Berne among a representative sample of 2,000 employed persons faced with an alternative is analyzed. The study on which the paper is based explores two directions: the first examines the perception of journey times and the second considers the rationality of users' modal choice with regard to real and perceived travel times. This dual analysis reveals that although users do not necessarily attempt to minimize their home-to-work travel time, they do try to avoid time spent travelling that is impossible to put to good use because of a lack of comfort or flexibility. Furthermore the results show that the quality of time and the speed at which time passes are linked: when use can be made of the journey time it passes quickly, when it cannot it passes slowly and is viewed in the same way as a long waiting time. Such poor quality is a frequent characteristic of public transport. Ultimately, the study shows that while the comparison between journey times is a criterion for modal choice it only takes on meaning in relation to the form and content of the time. While most respondents prefer their car to public transport it is as much on the grounds of flexibility and quality of the time as on the grounds of speed.     

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).     

Indicateurs de comparaison de scenarios prospectifs peut-on elargir le debat sur 1' avenir de la mobilite urbaine?

La construction de scenarios prospectifs de la mobilité urbaine vise généralement a faire émerger un débat sur les évolutions tendancielles, sur les inflexions qu'il conviendrait d'y apporter et sur les strategies a promouvoir. En tenant compte du cadre législatif dans lequel s'inscrivent les procedures de planification des transports a l'échelle locale, nous avons examine dans quelle mesure les indicateurs statistiques de comparaison des scenarios pouvaient s'adapter a la prise en compte des enjeux du développement durable et faciliter l'émergence d'un débat contradictoire autour de ces enjeux. Cet article expose les options méthodologiques générales retenues et fait un certain nombre de propositions concemant le contenu et la mise en forme des indicateurs a construire, en fonction des sujets abordés et des finalites de la démarche prospective.Urban travel prospective scenarios are generally constructed in order to stimulate debate on trends, on how these could be changed for the better, and on the strategies that should be promoted. While referring to the legal framework which applies to transport planning procedures at local level, this paper examines the extent to which the statistical indicators used to compare scenarios can be adapted in order to take account of the issues associated with sustainable development and facilitate the inauguration of an open debate around them. It sets out the general methodological choices that are made and makes a number of proposals about the form and content of the indicators that should be constructed, with reference to the topics covered and the aims of the prospective approach.     

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.     

L'entrée de la Cerdagne française dans l'espace économique barcelonais rôle de l'axe routier du Llobregat

Cerdanva is a mountainous trans-frontier region in the Pyrenees. Completion of the Barcelona-Bourg Madame section of the Barcelona-Toulouse motorway in 1995 brought Cerdanya to within a two-hour drive of Barcelona. This coincided with rising living standards in Catalonia and the creation of new affluent classes. The new road, which is known as the llobregat motorway, brought many more visitors to Spanish Cerdanya. The same occurred two years later from 1989–1990 in French Cerdanya. This increased cross-border traffic can be linked to increasing prosperity in French Cerdanya as witnessed by a rise in average taxable household income. At the same time a large number of properties. changed hands, most of them bought by people from Barcelona, and major property developers from Catalonia arrived in French Gerdanya. Leisure tourism seems to be bringing French Gerdanya into Barcelona's area of influence, which means that the economic and administrative borders are becoming dissociated.     

Gibraltar: le projet de lien fixe entre intégration euroméditerranéenne et développement régional

This paper presents a socioeconomic examination of the project for a fixed link in the Strait of Gibralter. This project for a major link between Europe and the Maghreb which would take the form of a rail tunnel can be examined at two different spatial scales, that of the major trade networks which link Europe and the Maghreb and that of the areas which are located near the future points of access to the tunnel. If we pass over the problems which may be posed by the financing of this project (which studies have shown to be profitable), the geopolitical context of changing relations within Europe and the Mediterranean should be favourable to its construction. Its strategic (and at the same time symbolic) character is defined by its role as a link between the trans-European networks and the southwestern shore of the Mediterranean basin. This physical connection may nevertheless generate undesired or even counterproductive effects in the directly exposed economies on the southern side. Additional strategies could be considered for which the existence of a tunnel would constitute an opportunity. These are referred to as accompanying measures in French regional planning policy.     

Une méthode d’analyse spatiale des espaces piétons au service d’un urbanisme orienté vers le rail ?

In recent years, the quest for a more sustainable urban planning and street design has gained importance among practitioners and researchers. An urbanism oriented towards rail is a valid alternative to the long standing practices of urban planning and street lay out based on the individual car, which have conditioned the development of cities for several decades. Among different tools that could be implemented to improve rail travel attractiveness, a radical improvement of walking conditions all along the footpaths leading to rail stations is proposed. In this paper, an observation grid as well as a set of criteria for footpath attractiveness are first proposed as a tool (or methodological approach) for a spatial diagnosis. This tool is then tested on the Carnot rail station in Saint-Etienne, a city in Eastern France. Besides the assessment itself (showing assets and challenges of the areas to be redesigned), this case study leads to proposed planning principles, in terms of recommendations meant to improve footpath quality significantly.     

Simulation des temps de parcours du transport ferroviaire régional du bassin de vie stéphanois dans le cadre du projet Bahn.Ville

The French-German research project Bahn.Ville, dealing with Rail oriented development and intermodality in German and French urban regions, has consisted in identifying the principles and factors of success of an urban development oriented towards rail, and in testing them in the agglomeration of Saint-Étienne. One of the research-actions focussed on identifying and anticipating the potential impacts in terms of urban development of a new transport system, of the tram-train type, on an existing railway line. The effect of the insertion of new stops on the global journey time is one of the criterion of the evaluation of new stops. A simulation method of the journey times is presented in this paper. The interest and the limits of this approach, regarding the rolling stock choice and the insertion of new stops, are emphasized.     

Entre marche et métro, les mouvements intra-urbains des touristes sous le prisme de l’? adhérence ? à Paris et en ?le-de-France

The urban movement of tourists remains largely unknown, but the mobility of tourists contributes to the metropolitan process. Around the notion of ??adherence??, this article demonstrates how, in the Paris metropole, tourists rely mainly on walking and the use of the tube to travel within the city. The structurally different characteristics of walking and the use of the tube represent a theoretical opposition between the two types of movements that are differently ??adherent?? to the city. However, these mobilities complement each other. Indeed, the partial disconnection of the tube is addressed by the direct connection and proximity to the city allowed by the pedestrian means.     

Modèles linéaires généralisés appliqués à l'étude des nombres d'accidents sur des sites routiers: Le modèle de Poisson et ses extensions

Models that link accident frequencies at road sites with traffic volumes and road characteristics provide reference values which are of value when carrying out diagnostic studies and deciding on preventive measures. Such models can be developed using generalized linear modelling techniques, which are able to take account of the Poisson properties of accident frequencies at road sites. The Poisson models obtained for road sites are frequently everdispersed, so extended forms of the Poisson model (quasi-Poisson, negative binomial a high percentage of the studied sites, in which case zero-inflated models also have to be considered. This paper presents an overview of these methods which are illustrated by modelling the relationship between accident frequency site characteristics and traffic volume on a large sample of bends.     

Quelle place pour la sécurité routière dans les plans de déplacements urbains? Entre intégration et diffusion,le cas du plan de déplacements urbains de Lille métropole

This paper describes the position given to road safety in Urban Travel Plans by analyzing Urban Travel Plan document from eleven cities and undertakes a more in-depth investigation of road safety in the Urban Community of Lille. These plans provide an opportunity to disseminate knowledge about road safety to the other areas of urban management. They also describe the beginning of an integration of road safety in urban planning, even if intersectoral approaches at city level have yet to be developed and even if, in the case of Lille, the division of institutional competence with regard to the management of public space still requires clarification.     

Réflexions sur le transfert méthodologique de l’analyse qualitative d’accidents de la circulation routière issue de l’étude détaillée des accidents (EDA) fran?aise aux procédures d’accidents colombiennes

Nearly 90% of the traffic accidents that occur worldwide happen in developing countries. Yet road safety remains a little-studied subject in these countries, and notably accidentology studies, which provide a wealth of information. One of the major problems in studying road accidents in developing countries lies in the lack of reliable accident data. Indeed, while the comprehensive accident analysis methodologies used in developed countries provide an understanding of the origin of accidents and accident processes, as well as making it possible to define suitable, effective actions, they require reliable and relatively detailed accident data. These methodologies are notably based on detailed accident studies (DASs) and their adaptation to the analysis of accident reports. Colombia has an infrastructure for gathering and storing traffic accident data that can be used to perform comprehensive accident analyses. This article defines the feasibility of a technology transfer (clinical accident analysis) to the Colombian equivalent of accident reports. These observations are part of a doctoral thesis prepared jointly by the IFSTTAR Accident Mechanisms Research Unit and the University of the Andes in Bogotá.