Why cities “flow”: an extract from Cities, a new book by Monica L. Smith

London from a hot air balloon. Image: Wikipedia via Creative Commons.

The whole point of maps and signposts is not to anchor us in place but to give us markers for movement. And movement is the hallmark of cities: people moving in from the countryside, visitors moving through the city on their way to somewhere else, and people moving among the city’s dispersed spaces of residence, work, worship, shopping, exercise, education, and intimacy. Even within a single neighborhood, there are many diverse places and pathways, all of which provide the opportunity for people to engage with constantly updated information inputs about goods, services, and events. Just being out in the streets provides, every day, the opportunity to do things slightly differently through changes of pace and direction. We walk straight and then turn left and right, or right and left, all of which lets us end up at the desired destination by picking our way through city streets with confidence.

The social theorist Mihaly Csikszentmihalyi has suggested that our sense of well-being comes about from the mastery of our surroundings and from the confidence of knowing the constraints through which we channel our energies. He calls this concept flow, in which optimal experience and happiness are gained through focused concentration. Interestingly, people achieve flow not when they are in a completely unfettered environment but because of the opposite: constraints actually enable people to concentrate their energies, resulting in an intensely focused outcome. Examples of flow-inducing activities range from rock climbing to surgery to playing games with one’s own children, in which people are “in the moment” in a way that supersedes perceptions of time and place, resulting in deep fulfilment. The fulfilment comes from negotiating mental constraints like the rules of a game, a musical score, or the logical steps of a complex operation. As Csikszentmihalyi states, “By far the overwhelming proportion of optimal experiences are reported to occur within sequences of activities that are goal-directed and bounded by rules—activities that require the investment of psychic energy, and that could not be done without the appropriate skills.”

In cities, we can think of flow as something that results from the physical constraints of the streets, bridges, and subway lines that channel our forward motion. The narrowing of passageways and the greater number of people traveling through them accelerate the very physics of what it means to be alive in a city, like a conduit that increases the speed of water as the diameter narrows. Cities have as their essence a continual sense of movement, starting at the very moment of urban formation when rural people move into the metropolis. From that initial settlement, the people who come into a city are joined by other kinetic forces. Itinerant traders loop in and out of the city with fresh vegetables from close-by farms and fields, while longer-distance traders come with grain and other food staples on a seasonal basis. Haulers bring in raw materials for urban workshops and take out bulk waste and recyclables. Suburban professionals—scribes, lawyers, accountants, middle managers—come in and out of the city on a daily commute. Weaving in and out from those pulsating waves are the urban residents who move around from home to work to recreation to food sources within tightly circumscribed neighborhoods. And the people themselves create a kind of constraint that adds to the creation of flow: coming into a city, you feel the clip of urban walk-worlds as something faster than a rural gait, and you find yourself stepping up the pace.


The physical constraints of cities have a spillover effect on social interactions in other ways as well. In a village, you can pick out a pathway depending on a few simple factors: Are you on good terms with that neighbor? Do you feel “at home” crossing that other person’s yard? By virtue of the village size and the fact that you had lived there for years, you’re likely to know quite a bit about those neighbors (including whether there was a large unfriendly hound in the yard). By contrast, people in cities are absolved from creating face-to-face relationships through the mute abstraction of the built environment and the sheer number of people. In a city, one needs to get from points A to B without having to personally know everyone else in the vicinity or without having to remember all of the social networks sustained among all those households. That anonymity of the greater urban realm removes the necessity for sustained social interactions and explains why you might look up and smile at passersby on a rural lane but rarely on a city street. The physical structures of cities—their formal routes, roads, and pathways, along with the written and unwritten rules for empty spaces like parks and plazas—all provide containers that simultaneously constrain physical opportunities and paradoxically free people from the cognitive overload of what would otherwise be an overwhelming number of social obligations just for the sake of movement.

Constricted spaces—crowded bridges, narrow streets, and narrower alleyways—were part of ancient cities, too. Excavations at places like Pompeii in Italy and the ancient Indus city of Mohenjo Daro in Pakistan have revealed a pedestrian cityscape that enables us to walk in the footsteps of our urban ancestors. Under the intense sun of midday, we can appreciate the shade cast by tall buildings while dodging the mad-dog blind alleys that abutted the major thoroughfares. At the ancient Mexican city of Teotihuacan, a century of digging has revealed grand boulevards as well as intricate little bylanes and courtyards within residential compounds. In those differentiated spaces, the ancient residents would have threaded their way through a maze of interconnected paths and experienced different rates and scales of flow as they moved about from day to day. Visitors today can still experience those spatial elements and retrace movements from the most intimate realm of the family hearth through the passageways of densely occupied neighborhoods to the massive pyramid complexes and the Avenue of the Dead.

Our understanding of the realm of motion in ancient sites comes from more than just appreciating their architecture. In moving along the pathways through neighborhoods and markets and temple plazas, ancient people left traces that we can actually see at the microscopic level. At the archaeological city of Kerkenes in Turkey, the archaeologist Scott Branting and his colleagues used an innovative sequence of techniques to show pedestrian movements. It would have taken centuries to excavate the entirety of Kerkenes, but a high-tech mapping process let them look at the layout of the buildings and streets like a geophysical “X-ray” in just a few summer months of fieldwork. The team made use of a survey method known as magnetic gradiometry, which reveals differential subsurface densities and results in a computer-generated map showing the outlines of structures in a ghostly version of the Nippur map or the Severan Marble Plan. Branting’s team then conducted surgically precise excavations in some of the streets. They collected materials from vertical slices of the street deposits that showed the layering effect of dust accumulation over time and looked at samples of the layered sediments under a microscope. The more rounded the sand particles, they reasoned, the more the pathways had been traversed. Every footfall rounded the grains of sand just a little more, and the cumulative effect of all that walking enabled the team to identify which streets were more popular than others and which ones carried the most traffic.

In Kerkenes, pedestrians flowed through networks of streets that crisscrossed the urban sphere, and evidence of that flow was right there under the microscope. Similar patterns of movement can be envisioned for every ancient city, in which the impact of each individual person could, in theory, be measured at the molecular level. The collective pattern of all of those individual interactions created a personal sense of flow but also resulted in a collective pattern of movement. High-frequency streets are places where we envision the presence of shops and market stalls, while low-traffic lanes wound their way through houses and alleys where few people had the need to be moving about. People going from high traffic areas to low traffic ones and back again took in the world around them as they walked or rode from one place to another, choosing their ways from among the many combinations of streets that would lead them from their residences, through their neighborhoods, to the monumental temples, palaces, and plazas of their metropolis.

Sometimes street layouts in ancient cities were the result of powerful decree and enforced consensus. We can see this thousands of years ago, when the gridded plan of the archaeological site of Sisupalgarh in India laid out a command of place that directed the flow of movement, just as we see the evidence for planning in relatively new modern cities like Washington, D.C., Brasília, and Chandigarh. Most often, however, the layout of ancient city streets was the result of incremental growth. This was particularly true at the start of urbanism six thousand years ago where the first inhabitants arrived with only their village experiences of ad hoc juxtaposition, as though plenty of space would always be available. Even after the organizational pattern of a city’s central area was well established, there was still a tendency to make new constructions with reference to the geometry of the nearest adjacent structure. The scholar Jeremy Till has called this the phenomenon of “architectural dependence,” in which there are few opportunities for entire built environments to start over from zero. Instead, the patterns established at the beginning of the construction process are the ones that continue to shape the creative potential of every subsequent generation.

In cities, the notion of architectural dependence constrains the near-constant sense of motion that is an essential part of urban life. From the time of the very first city, movement was channeled by the built environment; for the purposes of making one’s way through a space, a temporary building was just as much of a barrier as a permanent one. The resultant distinct flow within a city was thus neither mindless nor incidental but embedded and expressed in each architectural gesture and every pedestrian gait. In Chang’an, a great ancient capital of China that is just outside the modern metropolis of Xi’an, pathways and constructions provided not only an allowable flow but also moments of interrupted flow through structures that conveyed political authority. The palace, for example, sat athwart the traffic like a giant rock in a stream that otherwise passed to one side and the other. At Teotihuacan, the Sun Pyramid and the Feathered Serpent Pyramid were both very important structures, but their compounds were visually subordinate to the grand axis of the Moon

Pyramid and the Street of the Dead. In the Roman period, it was not just in Rome but in every city around the Mediterranean that “the street became a substantive building, a public building with a skylighted central tube of transit and shadowed aisles, that fell into uniform bays of pause. As such, it assembled the economic life of the city in shops and offices ranked behind its porticoes, subjecting to its spatial laws another of the daily routines of living.”

From the perspective of the thousands of ordinary people who took up residence in urban centers, it was those “daily routines of living” that made cities new and distinct and compelling. Compared with the dispersed landscapes of rural life and the intense family spaces of villages, the architecture of urban centers provided the opportunity for people to create close ties of their own design. Cities provided channels of movement in and around the many new types of buildings that had never before existed in permanent settlements: plazas that were larger than entire villages, and neighborhoods that mimicked the size of a village yet constituted just one tiny building block of an entire urban realm. Crowded streets of buildings and passageways provided new horizons that supplanted the natural skyline, making cities an anthropogenic maze. New verticalities of architecture, created for the first time in cities, invited people to look up. Just as for us the linearity of the internet has opened up an entire network of interconnected opportunities when one hyperlink leads to another, the built environment of cities resulted in a new circuitry of connections. Both the literal and the social flows of people were physically inscribed into the landscape, leaving us with the tangible remains of the past in the form of archaeological evidence.

Extracted from Cities: The First 6,000 Years by Monica L. Smith, £18.99, published by Simon & Schuster UK,

 
 
 
 

To build its emerging “megaregions”, the USA should turn to trains

Under construction: high speed rail in California. Image: Getty.

An extract from “Designing the Megaregion: Meeting Urban Challenges at a New Scale”, out now from Island Press.

A regional transportation system does not become balanced until all its parts are operating effectively. Highways, arterial streets, and local streets are essential, and every megaregion has them, although there is often a big backlog of needed repairs, especially for bridges. Airports for long-distance travel are also recognized as essential, and there are major airports in all the evolving megaregions. Both highways and airports are overloaded at peak periods in the megaregions because of gaps in the rest of the transportation system. Predictions for 2040, when the megaregions will be far more developed than they are today, show that there will be much worse traffic congestion and more airport delays.

What is needed to create a better balance? Passenger rail service that is fast enough to be competitive with driving and with some short airplane trips, commuter rail to major employment centers to take some travelers off highways, and improved local transit systems, especially those that make use of exclusive transit rights-of-way, again to reduce the number of cars on highways and arterial roads. Bicycle paths, sidewalks, and pedestrian paths are also important for reducing car trips in neighborhoods and business centers.

Implementing “fast enough” passenger rail

Long-distance Amtrak trains and commuter rail on conventional, unelectrified tracks are powered by diesel locomotives that can attain a maximum permitted speed of 79 miles per hour, which works out to average operating speeds of 30 to 50 miles per hour. At these speeds, trains are not competitive with driving or even short airline flights.

Trains that can attain 110 miles per hour and can operate at average speeds of 70 miles per hour are fast enough to help balance transportation in megaregions. A trip that takes two to three hours by rail can be competitive with a one-hour flight because of the need to allow an hour and a half or more to get to the boarding area through security, plus the time needed to pick up checked baggage. A two-to-three-hour train trip can be competitive with driving when the distance between destinations is more than two hundred miles – particularly for business travelers who want to sit and work on the train. Of course, the trains also have to be frequent enough, and the traveler’s destination needs to be easily reachable from a train station.

An important factor in reaching higher railway speeds is the recent federal law requiring all trains to have a positive train control safety system, where automated devices manage train separation to avoid collisions, as well as to prevent excessive speeds and deal with track repairs and other temporary situations. What are called high-speed trains in the United States, averaging 70 miles per hour, need gate controls at grade crossings, upgraded tracks, and trains with tilt technology – as on the Acela trains – to permit faster speeds around curves. The Virgin Trains in Florida have diesel-electric locomotives with an electrical generator on board that drives the train but is powered by a diesel engine. 

The faster the train needs to operate, the larger, and heavier, these diesel-electric locomotives have to be, setting an effective speed limit on this technology. The faster speeds possible on the portion of Amtrak’s Acela service north of New Haven, Connecticut, came after the entire line was electrified, as engines that get their power from lines along the track can be smaller and much lighter, and thus go faster. Catenary or third-rail electric trains, like Amtrak’s Acela, can attain speeds of 150 miles per hour, but only a few portions of the tracks now permit this, and average operating speeds are much lower.

Possible alternatives to fast enough trains

True electric high-speed rail can attain maximum operating speeds of 150 to 220 miles per hour, with average operating speeds from 120 to 200 miles per hour. These trains need their own grade-separated track structure, which means new alignments, which are expensive to build. In some places the property-acquisition problem may make a new alignment impossible, unless tunnels are used. True high speeds may be attained by the proposed Texas Central train from Dallas to Houston, and on some portions of the California High-Speed Rail line, should it ever be completed. All of the California line is to be electrified, but some sections will be conventional tracks so that average operating speeds will be lower.


Maglev technology is sometimes mentioned as the ultimate solution to attaining high-speed rail travel. A maglev train travels just above a guideway using magnetic levitation and is propelled by electromagnetic energy. There is an operating maglev train connecting the center of Shanghai to its Pudong International Airport. It can reach a top speed of 267 miles per hour, although its average speed is much lower, as the distance is short and most of the trip is spent getting up to speed or decelerating. The Chinese government has not, so far, used this technology in any other application while building a national system of long-distance, high-speed electric trains. However, there has been a recent announcement of a proposed Chinese maglev train that can attain speeds of 375 miles per hour.

The Hyperloop is a proposed technology that would, in theory, permit passenger trains to travel through large tubes from which all air has been evacuated, and would be even faster than today’s highest-speed trains. Elon Musk has formed a company to develop this virtually frictionless mode of travel, which would have speeds to make it competitive with medium- and even long-distance airplane travel. However, the Hyperloop technology is not yet ready to be applied to real travel situations, and the infrastructure to support it, whether an elevated system or a tunnel, will have all the problems of building conventional high-speed rail on separate guideways, and will also be even more expensive, as a tube has to be constructed as well as the train.

Megaregions need fast enough trains now

Even if new technology someday creates long-distance passenger trains with travel times competitive with airplanes, passenger traffic will still benefit from upgrading rail service to fast-enough trains for many of the trips within a megaregion, now and in the future. States already have the responsibility of financing passenger trains in megaregion rail corridors. Section 209 of the federal Passenger Rail Investment and Improvement Act of 2008 requires states to pay 85 percent of operating costs for all Amtrak routes of less than 750 miles (the legislation exempts the Northeast Corridor) as well as capital maintenance costs of the Amtrak equipment they use, plus support costs for such programs as safety and marketing. 

California’s Caltrans and Capitol Corridor Joint Powers Authority, Connecticut, Indiana, Illinois, Maine’s Northern New England Passenger Rail Authority, Massachusetts, Michigan, Missouri, New York, North Carolina, Oklahoma, Oregon, Pennsylvania, Texas, Vermont, Virginia, Washington, and Wisconsin all have agreements with Amtrak to operate their state corridor services. Amtrak has agreements with the freight railroads that own the tracks, and by law, its operations have priority over freight trains.

At present it appears that upgrading these corridor services to fast-enough trains will also be primarily the responsibility of the states, although they may be able to receive federal grants and loans. The track improvements being financed by the State of Michigan are an example of the way a state can take control over rail service. These tracks will eventually be part of 110-mile-per-hour service between Chicago and Detroit, with commitments from not just Michigan but also Illinois and Indiana. Fast-enough service between Chicago and Detroit could become a major organizer in an evolving megaregion, with stops at key cities along the way, including Kalamazoo, Battle Creek, and Ann Arbor. 

Cooperation among states for faster train service requires formal agreements, in this case, the Midwest Interstate Passenger Rail Compact. The participants are Illinois, Indiana, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, and Wisconsin. There is also an advocacy organization to support the objectives of the compact, the Midwest Interstate Passenger Rail Commission.

States could, in future, reach operating agreements with a private company such as Virgin Trains USA, but the private company would have to negotiate its own agreement with the freight railroads, and also negotiate its own dispatching priorities. Virgin Trains says in its prospectus that it can finance track improvements itself. If the Virgin Trains service in Florida proves to be profitable, it could lead to other private investments in fast-enough trains.

Jonathan Barnett is an emeritus Professor of Practice in City and Regional Planning, and former director of the Urban Design Program, at the University of Pennsylvania. 

This is an extract from “Designing the Megaregion: Meeting Urban Challenges at a New Scale”, published now by Island Press. You can find out more here.