Le cours présente un tour d’horizon introductif des interactions entre la mobilité et les dynamiques urbaines. Il propose des outils méthodologiques et opérationnels permettant d’appréhender et de réguler la mobilité. Ces vingt dernières années, la mobilité urbaine a beaucoup changé. Le nombre de déplacements de loisirs a augmenté tandis que la part des déplacements pour motif travail a diminué. Dans le même temps, de nouvelles formes de mobilités se sont développées, comme la multirésidentialité, la pendularité de longue distance, le tourisme urbain et l’excursionnisme. Ces changements ont été concommittants de transformations urbaines comme l’étalement urbain ou la fragmentation. Dans ce contexte, la mobilité est un enjeu pour l’ingénierie des transports urbains et le développement territorial, en particulier urbain: sa régulation nécessite une appréhension nouvelle de la demande de transport. Le cours montre ainsi aux étudiants les interrelations entre la ville et la mobilité, l’espace urbain et les flux de déplacements, tout en leur offrant une vision renouvelée du transport et de son impact sur le territoire et les modes de vie.
L'effet barbecue
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En provenance du cours de École Polytechnique Fédérale de Lausanne
Mobilité et urbanisme
63 notes
À partir de la leçon
La transformation des modes de vie urbains
L’objectif de ce second module est de montrer comment les territoires se sont progressivement transformés en lien avec l’évolution des potentiels de vitesses procurés par les systèmes de transports rapides, puis les technologies de l’information et de la communication.
Rencontrer les enseignants
Vincent KaufmannProfesseur
Laboratoire de Sociologie Urbaine, Faculté de l’Environnement Naturel, Architectural et Construit, École Polytechnique Fédérale de Lausanne
Aniss M. MezouedDocteur
Laboratoire de Sociologie Urbaine, Faculté de l’Environnement Naturel, Architectural et Construit, École Polytechnique Fédérale de Lausanne
Bernard DeclèveProfesseur
Faculté d’Architecture, d’ingénierie architecturale et d’urbanisme, Université catholique de Louvain
<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>
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