Introduction

<p>&nbsp;</p><p>“There remains a source of divergence among contributors: the preferred urban model for resolving the problems of congestion and pollution linked to the rise of urban mobilities. The opposition, which one might have thought we had left behind, between supporters of more compact towns and cities … and those who believe in a more diffuse urban environment, continues to flare up.”<a name="sdfootnote1anc" href="#sdfootnote1sym" class="sdfootnoteanc">¹</a></p><p>Is density an indispensible element in limiting greenhouse gas emissions produced by transport systems? In recent years, density has widely been seen as the key solution to the problem of saturated road networks and air pollution. From this perspective, the compact city offers the possibility of limiting distances to be travelled; favouring non-motorised modes of transport; and achieving the critical threshold beyond which it becomes possible to establish effective public transport etc.</p><p>However, the better match of dense urban forms to less polluting mobility tends to collide with individual preferences (for a way of life that guarantees spacious accommodation and possibly a garden) that make a major contribution to the spread of the peri-urban. At the same time, land and real estate markets are particularly tight in certain towns and cities, which tends to force people with lower incomes to move to the urban periphery.</p><p>In terms of practices, the ‘barbecue effect’ tends to qualify the supposed imbalance between greenhouse gas emissions of urban centres and those of the peri-urban: it highlights the lower level of greenhouse gas emissions linked to leisure travel in the peri-urban area, as illustrated in the use of the barbecue. Thus, although those living in the peri-urban cover longer distances and use their cars more often on a daily basis, during the weekends and holidays they travel shorter distances and use air travel less frequently.</p><p>And what happens if we take into account the greenhouse gas emissions produced by central heating? And those created by the transport of goods destined for households?</p><div id="sdfootnote1"><address><a name="sdfootnote1sym" href="#sdfootnote1anc">1 </a><span lang="fr-CH">Allemand S., Ascher F. &amp; J. Levy (dir.), 2004, </span><em><span lang="fr-CH">Les sens du mouvement</span></em><span lang="fr-CH">, Editions Belin, page 18.</span></address></div>