Time and the City

We sometimes think of the city as a collection of objects in space that exist for the purpose of reducing the costs of human interaction. The city is also a collection of objects in time. Taking the long view, cities once did not exist (the time before the founding of the city), and eventually may not exist again. The list of abandoned cities is long, and will eventually, though this may sadden us, grow longer.

However the city also operates at shorter timeframes. There is the multi-decade cycle of infrastructure renewal and replacement. There is the multi-year (though random) cycle of sports team victories. There is the annual cycle of the city operating through the seasons, with winter and spring and summer and fall events. There is the daily cycle of flows of people into and out of the city.


NoofTravelers TBI00

Why do we see diurnal patterns of flows? Why is there a morning and afternoon peak, or rush hour? The answer is to ensure some set of people (peak commuters) are generally in the same place at the same time. And we do this to reduce inter-personal coordination costs. If we are generally in the same place, we don't need to pre-arrange meetings, we run into each other in the hallways, I can easily knock on your door, I see you on the sidewalk. Our temporal coordination costs drop. And even if we do need to pre-arrange, it is relatively simple. As I tell my students in class: "I am here because you are here, you are here because I am here." In contrast, if we are not generally in the same place, we do need to pre-arrange meetings, I will not randomly run into you. Our temporal coordination costs rise.

There are lots of people for whom the congestion costs of the peak outweigh benefits of organizing work on the "standard" schedule. Many people with shifts in workplaces that operate more than 8 hours a day (medical, police and fire, manufacturing, transportation, retail, some construction, media) travel in the off-peak. For some this is necessary (you don't want to change bus drivers in the middle of the peak), for others convenience (why travel at rush hour when it is unnecessary).

In the Central Time Zone, that peaking pattern is partially dictated by what happens on the East coast. People here go to work earlier than they otherwise would to ensure a greater overlap in time at work with those back East. Similarly, people involved in international trade may keep odd hours locally to coordinate with their customers or clients elsewhere in the world. In other parts of the world, schedules similarly adapt to the needs of trade, as well as local custom. In some places, work lasts until very late, but there are mid-day breaks.

This temporal coordination imposes the cost of increased loads on the transportation system, as people converge and diverge at the same time, requiring either more capacity or more crowding (and slower speeds). We could (and do) smooth the flows on transportation systems, encouraging peak spreading (some of which the market does by itself) through differentiated prices.


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We can be spatially coordinated to reduce our scheduling costs, or we can be temporally coordinated so that we have lower space costs. The classic multi-purpose room in 1960s era Elementary schools, hot-desking, or shared parking between office, stadiums, retail, and churches are examples of a form of temporal coordination to share a scarce resource to reduce land and structure costs. Most temporal coordination though shares the scarce resource of the humans being on the same task at the same time, and thus requires more space. Typical cities provide both spatial and temporal coordination, putting people close together and having them do the same things at the same time.

Cities work to reduce temporal coordination costs, one of the many ways they enhance economies of agglomeration. But they do so by increasing spatial coordination costs. We cannot occupy the same latitude and longitude at the same time. If we want to do so, we must go vertical. This adds to the cost of construction. We do not have freedom to use our land any way we want to, we must share some rights to it, because society demands it. This diminishes our freedom of action.

One expects that improved information and communication technologies will reduce the need for in-person interaction, and we certainly see some of that. But reducing the call of the city does not eliminate it. So long as some physical interaction is required, cities of a form will emerge. The need for young men and young women of different genetic lines to somehow interact in person is one such call upon the pattern of the city.

Just as 200 years ago, the city was barely what it is today, 200 years from now, the city may differ again. Cities may return to being seasonal, like the classic Medieval trade fair. These once comprised entirely temporary structures, which gradually became permanent. Look at the Minnesota State Fairgrounds for a more recent example of the temporary becoming "permanent". Today we construct state fairs with permanent buildings, but world's fairs, which do not repeat annually, have temporary structures. While not made of paper mach´e, the buildings of Chicago's White City or even New York's 1963 World's Fair are largely gone. But the world's fair is a lot less significant than it once was.

If people lose their need for daily interaction, we should expect a thinning of the urban support system, less reliance on costly permanent infrastructure, and more reliance on the ad hoc. Humans will still require shelter, and those shelters may still cluster so long as transport still has costs, but we can easily imagine a world where advanced technology means we don't need to commute or shop more than weekly. And that means we don't need to live as close together. And with advanced driverless cars, even that burden (the need to focus on the task of driving) is lifted, enabling even more spread.

David Levinson

Network Reliability in Practice

Evolving Transportation Networks

Place and Plexus

The Transportation Experience

Access to Destinations

Assessing the Benefits and Costs of Intelligent Transportation Systems

Financing Transportation Networks

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This page contains a single entry by David Levinson published on February 4, 2013 10:43 AM.

The structure and evolution of a skyway network was the previous entry in this blog.

Does TTI underestimate historic congestion levels? is the next entry in this blog.

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