<I> (voice speaking in different languages) </ i> I will speak today about the barbecue effect. The barbecue effect, in fact, means a research track highlighted by some researchers. A line of research that seeks to question virtues that are frequently attributed to the dense city in terms of mobility. So what has led these researchers to formulate this line of research? What is it, this effect barbecue? And what questions raises it ? It's a bit the three questions that will structure my talk today. The barbecue effect is born of three observations. The first observation is that the urban form interacts heavily on the behaviors of individual mobilities. There are a lot of studies that show that dense habitat, town centers are associated with frequent use of public transport, walking, cycling, while the plated areas, peri-urban areas less dense, are associated with frequent use of the automotive and also significant distances for daily commuting. This link between urban form, in particular the density and mobility is quickly associated with the more or less durable nature of this mobility since we know that the car generates much more nuisance than other modes of transport, including an energy consumption far more important. It appeared that the dense city became the most urban form capable of generating a mobility more sustainable. This link between urban form and type of mobility generated was particularly highlighted by two Australian researchers, Newman and Kenworthy, who have linked urban density and energy consumption related to travel. And so on a sample of more than 30 cities worldwide, they highlight that the more dense a city is, the less important the energy-related travel consumption is. In contrast, the more it is spread over, the more massive the consumption is. So despite criticism towards their study, the curve the Newman and Kenworthy curve highlighting this link has greatly impressed people, including town planners, who today advocate the compact city to promote the emergence of a more sustainable mobility. Second observation: a whole lot of studies that are based, in particular that of Newman and Kenworthy, on the relationship between urban form and mobility, consider only the routine mobility, mobility conducted during the week. It is studies that do not take into consideration the leisure traffic, the mobility that is more occasional, less constraint, and thus more elusive. Third observation: this leisure traffic today is particularly important. It must be said that leisure occupies an essential place of our lifestyles. We still have more and more free time. Today, leisure mobility, in many countries, even constitutes the main reason for population travel, and this both in number of trips but also in distance. In Switzerland, for example, leisure mobility represent 37% of trips against only 23% for work and 22% for purchases. In addition, these leisure trips, which are numerous, are frequently made with high consumer of energy transport: the car, and especially the plane. So from these three findings was born the following question: is this link between urban form and mobility they often highlighted, the same when we take into account all mobility achieved by urban people, including leisure mobility, including mobility realized on a long distance by plane? One of the answers given to this question, it is the barbecue effect. The barbecue effect was stated at the beginning of the 2000s by two French researchers, Jean-Pierre and Daniel Orfeuil Soleyret who were interested in the interactions between local short distance mobility and long distance mobility, on weekdays and during weekends in France. In their study, they demonstrate that inhabitants of central areas, of dense areas, of inner cities, travel more frequently for leisure than people from more sprawling suburban areas. And this difference is explained by them that suburban, residents of suburban housing have a residential environment more favorable to spend their free time, including a garden or have forests nearby. In contrast, city center dwellers should offset this lack of green or environmental nature in their everyday environment and move more frequently to enjoy it. So the two researchers call this effect "barbecue" named frim this traditional activity, easily achievable in the outskirts, and less practical in the city center. In addition, they highlight the fact that these leisure travel, as they are made by plane and over very long distances, are able to squarely challenge the very clear relationship we highlighted so far between urban form and mobility. So, according to them, we would have, if we took into account that leisure traffic, a curve that would have a different look. The higher the density, the more the movements comsume energy. Eventually, this work led to question the urban density and its virtues. Is this density so beneficial that if, ultimately, drives urban people to flee the city and to seek opportunities they do not have by plane and consume a lot of energy for this? In my view, the barbecue effect raises three issues that are so much interesting research paths. First of all, the mechanisms of influence. The researchers demonstrated statistical connections, but ultimately, what pushes the inner city to travel frequently and over long distances? Compared to the barbecue effect, I hypothesize thaht the inner city have lifestyles that include long-distance travel. But these long-distance trips are not all of the same type. Some of these movements are related, actually, with the search for nature, fresh air, pleasant environments they do not have every day. These movements can be called compensatory as they will compensate a residential environment they do not daily have elsewhere. But there are other types of leisure trips also very important. These are movements to find a city elsewhere, to seek urban opportunities elsewhere. Examples are all the weekends that are made by urban people in other cities, particularly through the development of low-cost airlines. So the barbecue effect highlighted by Jean-Pierre Orfeuil and Soleyret, would affect only a part of these movements. That's an assumption I do. Second question and second line of research, the magnitude of this barbecue effect. Is it really capable of challenging the virtues of the dense city? If one is interested only in a certain kind of movement, compensatory movements precisely, it can be assumed that based on certain characteristics of cities, including their size and accessibility by public transport with the hinterland of the urban area in question, the compensatory movements can be achieved over shorter distances and also with other means of transport than the car. And in this case, these compensatory movements would have an energy balance, environmental impact that would be weaker. So it may be that the city centers of the same density, depending oo these criteria, do not generate similar compensating movements and in some cases, these compensatory movements do not reverse the curve of Newman and Kenworthy and the dense city keeps all its advantages in regards to mobility. Again, an open question. And then, the last line of research, can we finally act on the city, build the city differently to generate less compensatory movements to reduce this barbecue effect ? The question is, what would look like urban life enrionments who have both virtues of dense city, and also, that would present interesting opportunities for leisure, for residents of town centers, so they won't spend a lot of energy to move a lot to join the opportunities they do not have close by ? And in this field, a question also essential: Is that, really, possible to act on leisure mobility knowing that, in this area, the displacement is something that permeates many performances. For many, in fact, the holidays are just synonymous to departure, to mobility, and this very strong association is completely independent from residential contexts, eventually. So it would ultimately be futile to challenge the dense city to act on these trips, which we would have an incompressible balance. So there, too, is an open question that should be explored. These are the three trailss of research around the barbecue effect that I strive to continue in my PhD research which covers the cities of Geneva and Zurich, so a research that combines quantitative and qualitative method, and of which I might soon, I hope, present to you the main conclusions. <I> (voice speaking in different languages) </ i> <I> (voice speaking in different languages) </ i>
