Evolution vs. Plans


Assuming we started with an undeveloped wilderness,  cities emerge at selected points (typically points with natural accessibility advantages over their neighbors, such as ports and harbors, or water falls, or railroad junctions). But they evolve from wilderness to city over time.

They do not generally evolve because someone built city-scale transportation out in the country and waited for the people to arrive.

Instead it is a ratchet: a few people, some transportation network investment; some more people, more investment; even more people, still more investment, and so on, until something resembling a city emerged.

While the infrastructure may slightly lead the development (as in the Streetcar Suburbs or London’s Underground) those developments in general contiguously extended the urban environment in appropriate steps, and were accompanied by development in the near term (failure to see development would have led to bankruptcy for the line).


Plans aim to take this chaotic, unpredictable, evolutionary process and put a sheen of order upon it.

The general problem with public sector transportation and land use plans is that they are static. They are made for one point in time. They are  snapshots in a world with 24 frames per second (for eternity), and for which we don’t know the ending (“no spoilers”).

Life-cycle of rail in the US. From The Transportation Experience, Figure 6-4
Life-cycle of rail in the US. From The Transportation Experience, Figure 6-4


They design for maturity and implicitly assume that the mature (built out) city sustains. The evidence from the life-cycle for every mode (or technology) is that its scope and extent are continuously changing.

The mirror of this problem is  they ignore the path that gets you there and all interim states, as well as changes in behavior and technology that may occur in the interim.

The third problem with plans is that they address future problems that don’t exist today, when there are plenty of problems today that remain unsolved. Trying to better manage how will people get around or from or to a site which might (or might not) transform from country to city, or even low density suburb to high density suburb, in 30 years when there are plenty of ways to help people get around better today is an exercise in pointlessness, whose primary objective is to transfer resources from the public to selected (and one presumes politically influential) landholders.

There is nothing wrong with having a vision. It presents a direction in which to proceed. The most important thing is the next step (or two) though. Each step you take in one direction is a step farther away from destinations in other directions. But the path on which we are walking is shrouded in smog. Our vision is simply our imagination (or consensual hallucination) of what lies down the road. We have never been there before. But we must recognize, we never will reach where we think we are going.

On “Induced Demand”


JW Writes:

I strongly agree with David King’s recent post that we so often forget accumulated knowledge and that we seem to re-discover this knowledge in endless cycles. Nowhere does this seem more true than in the field of economics, which brings me to the reason I reacted so strongly to David’s post.

I hate the term “Induced Demand”. I hate the idea that induced demand is something bad; something to be avoided.

In economics 101 we learn that demand is a function – not an amount. It is presented to us as a two-dimensional function. To make the math easy, it is then reduced to a one dimensional (linear) function so we can calculate elasticity and solve problems. In fact, demand is a three dimensional function, with time parameters, and is not a zero dimensionless point.

We only arrive at an amount (of travel) when we intersect the supply function with the demand function. Transportation improvements, whether the construction of a new runway at an airport or the signal coordination along an urban arterial, change the supply function, and therefore the amount of travel consumed, and the price.

When we consume travel, we are actually consuming something else. It is instructive to think in terms of David Levinson’s formulation of “access” instead of travel. Access is a Merit Good. Merit goods are what most people think of when they talk about Public Goods, without the messiness of concerning ourselves with rivalry and excludability. Merit goods are normally associated with positive externalities; and as such are considered to be something that individuals or societies should have on the basis of need; and something that will be under-supplied by the market, making public provision desirable.

From the individual’s point of view, access provides opportunities to more jobs, more entertainment and social options, and more alternatives for consumption of goods and services. From a business’ point of view, access provides a larger pool of labor and more raw materials. From a retailer’s point of view, access provides a larger pool of consumers. From a municipal government’s point of view, access allows more efficient provision of police protection, fire protection and ambulance service by reducing the number of facilities necessary for a given response time.

Transportation improvements that provide greater access per unit of time lower transaction costs. Lower transaction cost lead to great efficiency in the economy and a higher standard of living.

In telecommunications networks we have witnessed several orders of magnitude improvement in capacity during our lifetimes, yet we have always filled the new capacity. We stream video now when we used send text files. Yet no one wrings their hands about the induced demand in our telecommunications network.