Here is an interesting study published in Nature Cities called “Hidden patterns of urban mixing across five global cities.” The study leverages individual-level travel data, covering over 200,000 residents in Boston, Chicago, Hong Kong, London, and São Paulo, to analyze the amount of social mixing that tends to occur across different socioeconomic groups within these cities. To be more precise, the study measures collocation among different segments — people within the same urban spaces at the same time.
Two findings stood out to me.
First, public transit is a key ingredient in increasing social mixing. It does this because it centralizes activity and delivers a broad cross-section of people to amenity-rich destinations, rather than encouraging decentralization. It is for this reason that “the gap in social mixing between low and high income is smaller in Hong Kong and London than in the other three cities.” Destination amenities explain 50-69% of individual social mixing levels, according to the study.
Second, the study finds support for something known as the “second youth” hypothesis. This is a documented phenomenon where people, right after the typical retirement age (ages 65-74), exhibit an increase in social interaction and mixing. Another term for this is the Third Age, which is the active post-retirement period that people live after their Second Age (employment and family formation) and their First Age (childhood, education, and dependency). This makes sense given that retirement frees up time!
Both of these findings (as well as the other ones in the report) offer lessons for city builders. Public transit and density are the great urban unifiers. They, quite literally, bring people together. At the same time, it’s a reminder that our challenge is to design our urban centres and public spaces for the full human lifecycle: young people, families, retirees living their best lives, and everyone else.