To a Minnesotan like me, the public transit in Milan, Italy is so good that it’s both stunning and frustrating. It stuns because it is so efficient, practical and widely utilized, and it frustrates because my own transit system in the Twin Cities is so brutally inferior. 

More People, Fewer Problems

At rush hour, four different subway lines come every three minutes, while the Twin Cities offer a measly two rail lines coming every 15 minutes. Half past 1 on Saturday nights, Milanese buses don’t even have any seats available. Walking a couple blocks in any direction seems to take you to some kind of transit stop. 

Many things about Milan, where I am studying this spring semester, are quite different from the Twin Cities. But the city’s distribution of people might be the single most important difference behind the city’s superior transit system.

This argument is advanced by the urban economist Alain Bertraud in a paper titled “The Spatial Organization of Cities.” Bertraud argues that the distribution of people in a city — as measured by its population density and its monocentricity — defines a city’s capacity for public transit. Milan is dense and built around a clear city center; the Twin Cities are much less dense and organized around multiple, weaker city centers. These two characteristics deeply influence each urban area’s transit, enabling a highly effective transit system in one city and restricting a lackluster system in the other.

Let’s take each characteristic in turn. Population density’s influence on transit is fairly intuitive: the denser a city is, the more people are moving around in a given area. Each transit stop sees more travelers getting on and off, and so running frequent routes with comprehensive coverage makes sense. 

Bertraud illustrates this point by comparing Atlanta and Barcelona, which in 2005 had comparable populations and fairly similar lengths of metro networks. But in more sparsely-populated Atlanta, almost none of the population lives near transit stops, and so it’s hardly surprising that transit represents a marginal proportion of trips. With its low density, Atlanta would have to increase its metro network length by about 45 times if they wanted to match Barcelona’s population coverage.

Does the (City) Center Hold?

It’s not just the density of people that influences how well transit can work, however. Equally important is how those people are spatially distributed. Cities that are monocentric — that have a single, predominant center of population, jobs and amenities — are much more favorable to public transit than polycentric ones. 

In monocentric cities, people making trips (to work, play, visit others, etc.) are typically going to and from a cluster of destinations in the center, and public transit can capitalize on these common routes. Polycentric cities face a greater challenge because trips neither start nor end at any concentrated center. In two hypothetical cities with the same population density, the monocentric one will more easily support effective transit coverage.

Milan has a clear city center where most urban activity happens, and this centrality is reflected in the city’s transit network. On a map of the city’s four operating underground light rail lines, you can see that there is a clustered center area through which all rail lines pass on their way to and from the outer areas. 

While the Minneapolis core acts as a relatively predominant center for the Twin Cities, it is not monocentric in the same way that Milan is. People’s local trips are much more varied; the transit system is less likely to have well-serviced “core routes” because the core routes are not as well-defined.

Urban form is not the sole reason for weak transit in the Twin Cities (and across the country). We don’t always nail practical planning choices, picking routes that don’t make sense or stop too frequently. Likewise for implementation — even the best transit lines can get bogged down by traffic and poorly-timed red lights. We need to make political decisions to invest in transit; even if demand for transit greatly increased we’d still need to address driver shortages. Even when we do sizably invest in transit, the dollars don’t always go far, with recent research highlighting the overspending omnipresent in American transit construction.

Yet while these other factors also define the quality and quantity of our transit systems, our urban form shapes the space of viable transit paradigms. We should address these other transit challenges in the Twin Cities and elsewhere. But improving the Twin Cities’ transit network with our current population distribution is like walking through molasses upriver. 

Transforming Our Urban Form

In his paper, Bertaud warns us that “urban shapes are path dependent. The spatial structure of large cities evolves very slowly and can evolve only in a few directions.” We will never shrink Atlanta into a city as dense as Barcelona, or reshape the Twin Cities into a Milan-style monocentric urban area.

However, this lens also points us towards policy decisions that are within reach and would contribute to a better transit system. At the local and regional level, we could improve our decision-making around land use regulations and infrastructure investments to foster an urban form that would support effective public transit.

The land use improvements that we can make are fairly familiar. Generally, any form of regulation that restricts urban development — apartment bans, minimum lot sizes, strict height limits, etc. — will both lower density and weaken a city’s monocentricity by dispersing people over more land. Allowing large apartments throughout core cities, missing middle housing in single-family neighborhoods and smaller lots in inner-ring suburbs will each help improve the conditions for transit.

Infrastructurally, we ought to reconsider decisions that favor suburbanization. Our highway system is one of our most substantial infrastructural investments, and it creates an urban form much less amenable to transit. Economist Nathaniel Baum-Snow estimates that a highway built through a city historically caused an 18% reduction in the central city population by enabling suburbanization. Such investments may have benefited those who gained access to cheap suburban land, but they also sucked out demand for urban transit systems. Alternative infrastructural investments that make denser living more functional — good bike infrastructure, well-maintained public space — will help cities densify and support a basis for better transit.

Even under “optimal” policy, urban form will change slowly. But even slow changes toward a different population distribution would make our transit challenges substantially more solvable.

Photo at top courtesy of https://structurae.net/en/structures/gioia-metro-station