The Concrete Fallacy

The “Concrete Fallacy” succinctly defined is the erroneous belief that building public transit infrastructure within a given neighborhood is the investment that maximizes that neighborhood’s per dollar utility. In simpler words, a useful infrastructure project in the neighborhood may be less useful for said neighborhood than an infrastructure project outside the neighborhood. Note that this fallacy applies to road networks too, but this post will focus on public transit, as people fall for the fallacy less when thinking about road networks.

The basic fact that makes the concrete fallacy possible is that transit trips, by definition, do not start and end at the same location. The speed at which one can traverse any particular part of the trip is equally important as any other part.

Let’s say you work in a neighborhood called Jobville. It isn’t particularly valuable for transit to move really fast in your home residential neighborhood if you just get stuck in horrible traffic near your job in Jobville anyways. In fact, you may find it more valuable for the transit agency to spend some money getting the bus out of traffic in Jobville so that you don’t have to waste 10 minutes each day sitting in traffic to traverse the final mile of your commute. Saving those 10 minutes near work can far outweigh any value dedicated right of way or other improvements near your relatively traffic free home could possibly bring (especially if your bus spends less than 10 minutes in your neighborhood!). Failure to realize where capital investment would most help you is to succumb to the concrete fallacy.

Of course on the individual level people rarely make this mistake, as the costs and benefits will be readily apparent. But on the neighborhood level the concrete fallacy is still a trap because most of your neighbors don’t work where you work and don’t see the value in spending transit dollars near there. There may be a fraction of people in your neighborhood that work in that area, but not nearly enough to make the immense benefits to you and those with a similar commute, outweigh the near uselessness of the investment for everyone else in the neighborhood. In this instance, your neighborhood is likely to support the investment of dollars locally. Small benefits to a large swath of neighborhood residents will be viewed as superior to acute benefits for a smaller subset of neighbors. Moreover, if you are not actually planning to regularly use the service, it is easier to see how an investment physically located in your neighborhood will benifit you and your community than one outside the neighborhood.

Up to this point I have been discussing what I’d describe as the strict concrete fallacy, wherein the benefits of capital investment in the neighborhood is less valuable for the neighborhood than investing those same dollars elsewhere. However, the more common concrete fallacy occurs when we consider many neighborhoods making spending decisions.

Let’s use the Jobville example again. In all likelihood, your residential neighborhood isn’t the only neighborhood from which people commute to Jobville, assuming it contains enough density, employment, and activities to attract people from a wide variety of neighborhoods similar to yours. If those neighborhoods pool their money together to improve trip times near Jobville, each neighborhood only pays a small fraction of the total cost of the project. So while forking up for the entire project doesn’t pencil out for any given neighborhood, the coordinated spending in Jobville may benefit the average resident of each neighborhood much more than each neighborhood spending their money locally.

Mathematically we can say that if N is the number of neighborhoods, X is the value of a local project for the neighborhood and Y is the value of the Jobville project for each neighborhood and the costs for the projects are Xc for each local project and Yc for the single Jobville project then choosing the Jobville project is the optimal outcome for each neighborhood if:

Y – (Yc/N) > X – Xc

For example, if the value in each neighborhood for the Jobville project is 12, the cost of the project is 50, the value of each local project is 15 and the cost is 11 and there are 10 neighborhoods then: 12 – 50/10 = 7 > 4 = 15  – 11.

Note that this equation does not include the residents of Jobville in calculating the merits of the project. If Jobville is mixed-use then they will presumably also benefit from the capital investment in their neighborhood. Indeed, this subtlety is a key aspect of the concrete fallacy. When people look at a map they often instinctively view rail in another neighborhood as for other people (in this case the residents of Jobville) even if it is not just for people living there but also people who want to go there, including some of their neighbors.

The concrete fallacy is insideious and has a tremendous effect on rail planning. Instead of investing in a denser rail network in the center of the city, regions tend to build large sprawling rail systems. These sprawling systems serve people’s desire to “have rail in their neighborhood,” but tend to fail to actually provide all that much mobility for those neighborhoods because they don’t effectively serve enough destinations where people from all over the city actually want to go.


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