"The physical environment is an important variable that affects the behaviours and the well-being (Gärling & Evans, 1991). Any arranged space constitutes at the same time a sum of constraints and objective and subjective potentialities, perceived and lived by the individuals (Fischer, 1992). Perception evokes cognitive and emotional processes allowing us to establish judgements on the quality of the places. It takes various forms and results from individual and collective experiments. It is influenced by our needs as well as social and cultural affinities (Moch & Maramotti, 1995, Moser, 1992). Moreover, the installation of public space constitutes a fundamental element of our daily framework of existence (leading to behaviours supporting isolation or sociability). This installation has an influence on social relations in public places. A study by Carles and Lopez Barrio (2000) showed that the configuration of the installation of urban space influences sound perception and the perceived safety of the residents. In the same way, Snowdon (2000) underlined the impact of the vegetation on the social relations. This study proposes to explore the impact of the physical environment (installation of "30 zones") in two Parisian districts entailing new installations. We compared thereafter the perception of the "30 zone" to the perception of streets without changes in road systems. We make the assumption that within this privileged environmental framework (30 zones) the quality of social relations would be better than in the other streets. The "30 zone" is a homogeneous area of circulation where speed is limited to 30kph (20 miles/h) and whose entries and exists are announced by road signs."