Transportation demand management…what?

Project: Design a transportation demand management study to help determine future transportation needs and policies at IU.


Transportation demand management is quite a mouthful, both to say and to tackle as a conceptual matter. Six weeks ago – before I started my internship with the Indiana University Office of Sustainability – I couldn’t have told you more about it than it probably had something to do with managing the demand for various forms of transportation.

Which isn’t actually far from the truth. Transportation demand management, as a discipline, is really the second generation (or, some would argue, third or fourth generation) of transportation management mechanisms, and, unlike earlier generations, approaches management from the demand-side. Transportation demand management, or TDM for short, centers on the question, What can we do as planners and managers of transportation systems to influence the demand for certain (generally, more socially beneficial) modes of transportation? TDM is the so-called second-generation approach because it succeeds a planning approach called transportation system management, which was largely supply-side focused, asking and answering questions such as How can we (transportation system managers) best increase highway capacity so as to alleviate congestion?; or, How can we supply more roads more quickly to keep up with the increasing number of automobiles on these roads? In contrast, TDM asks how we can better manage demand – namely, the manifestation of people’s transportation preferences in the form of their travel behavior – for these roads and highways (and buses, rail, and sidewalks, too).

As I have been researching TDM these past few weeks, I have been learning both about the basic principles of TDM itself, such as parking pricing, toll roads, marketing and advertising, and incentives (more on these later, perhaps in another blog post), but also about systems of thought that might inform how we think about a so-called “transportation demand management problem” and, thus, influence how a study in TDM might be conceptualized.

Pause. All this sounds confusing, right? Generations of transportation planning? Conceptualizing a study? Managing a transportation system? Manifestation of preferences in behavior? Let me explain what I mean.

How transportation works: Transportation essentially consists of four decisions to be made by a “consumer” of transportation. First, the decision must be made of where to go. Second, when to go there. Third, how to get there or what mode of transportation to use. And finally, what route to take. In aggregate, this amounts to a society of people that are in one place, need to get to a different place, need to get there at a certain time, and via a specific mode of transportation. This clearly presents quite the complicated problem for the researcher of transportation dynamics. Variation in the results of these four decisions made by the consumer vary in both time and space, with age and other demographic and economic traits of the individual, and the decisions made are specific to a given location and context, i.e. the transportation network of the place within which travel is to occur. More often than not these days, with over 50% of the world’s population living in urban areas for the first time in history, that place is a city.

Managing transportation: In order to manage the transportation occurring as a result of the aforementioned decisions of consumers, there are several actions a manager or planner can take. One can provide incentives that make one form of transportation relatively more desirable than another, such as providing free bus passes to employees of the municipal government, or providing a cash payout to students on a university campus who choose not to purchase a parking pass, both mechanisms aimed at decreasing demand for single-occupancy vehicles and thus reduce congestion. A public transit agency could also increase marketing and advertising for its services as a means of increasing demand for public transit. Of course, the very notion of managing and influencing the decisions individuals make with regards to their transportation behavior carries a heavy demand-side bias. Alternatively, altering the transportation system itself – through widening of roads in an attempt to decrease congestion, expanding public transit service to increase capacity and handle an increasing number of riders, or building additional parking structures to house the increasing number of cars driven to a central business district – is a supply-side approach to transportation management. Many transportation experts call this supply-side approach to dealing with congestion or parking problems an attempt to “build a way out” of the problem.

Fortunately – for proponents of pleasant city streetscapes, sustainability buffs, and sprawl-haters alike – this supply-side based transportation system management is being replaced, at least in research circles if not yet always in practice, with transportation demand management. As I’ve mentioned before, TDM is the focus of the study I will be designing this summer for the Indiana University Office of Sustainability, in an effort to begin gathering data to better understand what I’m calling ‘the transportation problem’ at IU.

Which brings me to the issue of conceptualizing a problem: As mentioned above, the four decisions made by individuals as well as the results of these decisions present a challenge for conceptualizing and formulating the problem for a city transportation management organization or planning agency. What types of issues are to be included in any analysis of the problem? Do we include the land use patterns of a city? Asking this question yields a less obvious answer than one might think. Land use defines the type of activities occurring within a particular plot of land, and thus, the particular types of people who might want to visit that area. However, while land use is clearly linked to transportation needs, researchers often have a difficult time modeling the affect of one on the other. This is largely because historically our land use evolved around our transportation system – namely, the US highway system – rather than the latter being designed to serve the former, as one would think perhaps makes more sense. Thus, this creates a problem when deciding whether or not to include land use as a variable in any sort of characterization of a transportation system. Land use is just one of several issues that pose challenges in transportation analysis. Activity patterns of individuals; the influence of preferences on behaviors (which in turn influence demand); the differences between preferences, behavior, and demand; the economic paradigm within which transportation supply and demand are viewed; the role chance, uncertainty, and risk are given in the problem; the boundaries drawn around the problem and any unintended consequences that may be overlooked as a result of those boundaries; the degree of flexibility and adaptability of the administrative system associated with and governing the transportation system, not to mention that of the infrastructure itself (which is generally, little); whether the problem is viewed as static or dynamic, and if dynamic, whether it is tending towards a single equilibrium or multiple possible equilibrium, and whether lock in to a particular equilibrium will impose additional constraints on the analysis – all these and more color the lens of the transportation researcher or manager.

There are many, many more issues I could list associated with creating a transportation demand management study. My job this summer is to investigate as many as possible and attempt to determine the best way to characterize, that is, to frame, our problem in transportation at IU and in the immediate Bloomington community; and, then, to design a study to gather the data needed to properly manage, if not rectify, this problem.

Or multiple problems. I’ll keep you posted.


2 responses to this post.

  1. Jess, why would you pick a project whose acronym reads “tedium”? 🙂

    Just joking. Actually, by some weird coincidence, I was discussing Trinidad’s transportation problem with my host this morning. We were in the car at 5 am (and you know me, I’m not a morning person), heading to Port of Spain, the capital city, which is in the north of the island and is the centre for most businesses and almost all governmental offices. It is quite common for people to live in other parts of the island and commute to Port of Spain everyday via the only existing north-south highway. It is no easy undertaking, because traffic jams begin as early as 6 am. and continue all the way to 9 am. then repeat around lunchtime and in the evenings when everyone returns home.

    The previous administration tried several measures to curb this traffic. First, they tried increasing the number of lanes on the highway, but this only had the effect of creating a bottleneck on the outskirts of Port of Spain. Second, they introduced a bus system, which many people, admittedly, use, but which has the disadvantage of travelling only once a day, leaving from the south at 5 am and reaching Port of Spain by 7:30 am, and then leaving Port of Spain at 4:30 pm to get back at 7 pm. Now, there are only so many people that can fit on a bus, especially one that makes only a single journey everyday.

    Then there are the water taxis. These run daily (except at present, due to rough seas), but they aren’t used as much as they should be, perhaps because of poor advertising/marketing. And then, as a worker, you have to make your way from the port to your place of work in Port of Spain, which presents its own challenges. Many prefer to use their cars. And finally, there are the Priority Bus Routes, which are now going to be opened up to the public at selected times during the day to ease traffic congestion, thereby undoing the idea of a PBR in the first place.

    It is a knotty problem, not easily solved. And yet, as I read your post, I realized that they were, as you put it, “supply-side focused,” mostly trying to accommodate people rather than change the way they travel. Granted, the water taxis and PBRs might influence people’s demand slightly, but it is far from sufficient (and evidence thus far shows that it is accompanied by problems of its own).

    I enjoyed this post, especially because of its relevance to my current situation. I’d love to hear more about the project as it progresses. Keep up the great work, Jess!

  2. Posted by Jess Vogt on June 25, 2010 at 10:27 AM

    Wow. I had never realized the appropriateness of that acronym, now that you literally spell it out for me.

    And your comment rings true for almost every large global city with traffic problems. There are people working to change things, focusing on the “demand side,” but not nearly enough, and not nearly in as systematic a fashion as is necessary to effective increase people’s mobility, decrease auto-generated pollutants, and truly make cities “livable.” Some European cities are getting there, and Portland or Boulder or Seattle – or even parts of NYC – in the US might be coming close, too, but I’m finding it hard to extend these “big city” examples to the paltry-in-comparison small-town Bloomington/IU “traffic problems.”

    I have, as of yet, to make any headway.

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