TDM is Not Scary: A 101 on Transportation Demand Management

“How do we begin to covet, Clarisse? Do we seek out things to covet? No, we covet what we see every day.” – Hannibal Lecter in Thomas Harris’s Silence of the Lambs

Here at Mobility Lab, we share stories about transportation options that are “cool, healthy, fun, and efficient.” The thing is: these stories are about something that most people don’t see or covet (or relate to) all the time. People in the U.S. see cars, not pedestrians, vanpoolers, and bicyclists.

But let me pull back the curtain a bit to reveal our actual business, that of “transportation demand management,” or TDM.

The term TDM may occasionally show up in our stories, but unless you’re a complete transportation wonk, you probably don’t know what it means, let alone why it matters.

It should be noted that there are perhaps as many perspectives on TDM as there are employees at Mobility Lab, so don’t be fooled by the title of this blog: this is one writer’s “101” understanding of the topic, not a consensus.

While nothing presented here is patently untrue, another writer could define TDM from one of many other perspectives, since TDM is as interdisciplinary a field as urban planning itself, encompassing elements of economics, sociology, marketing, engineering, information technology, and urban design, among others.

Wikipedia defines TDM as the “application of strategies and policies to reduce travel demand (specifically that of single-occupancy private vehicles), or to redistribute this demand in space or in time.” In other words, TDM is about changing the behaviors of commuters in order to achieve that elusive perfect blend of walking, biking, transit, and driving.

Generally the field has tended to focus on the low-hanging fruit, that of single-occupancy vehicles, encouraging their drivers to choose a different mode of transportation. But TDM is really about spreading out the demand for transportation across all available modes.

TDM has come into increased favor in the United States in recent years as planners have realized that it’s much cheaper to proactively manage (or attempt to manipulate) the demand on a transportation network – or a system of roads – than it is to increase capacity on that same network. The economic return on investment of TDM means that policy makers too are starting to pay attention.

Americans today are sophisticated enough to understand that adding a lane onto an interstate isn’t any kind of long-term solution to congestion, as that new lane almost always instantly fills to capacity (not unlike water in a larger pipe).

A case study in this issue can be seen in Arlington County’s decision in the 1970s to push back against the federal government’s intention to widen Interstate 66. An audacious proposal at the time, it is viewed by many today as textbook good urban planning. Forward-thinking vision, quality city planning, transit-oriented development, and implementation of TDM, among other strategies, have been key elements in transforming Arlington County from the bedroom community and suburb it was in the ’70s to the highly successful urban center and economic engine it is today.

So let’s get back to that single-occupancy vehicle, or SOV: the main cause of congestion on our roadways. The driver of this vehicle isn’t a bad guy (unless he is Hannibal Lecter). He is like many of the readers of this site, in fact, making choices in response to the million or so messages he’s been fed by the media that have led him to equate the automobile with sex, freedom, and wealth. His response is akin to Mr. Lecter’s quote at the start of this article: he thinks he’s making a rational choice, but it’s really being made for him, more or less. Garbage in, garbage out.

“TDM is about choices,” explains Stephen Crim, research manager at Mobility Lab. “Every day people make choices, of where to live, how to get around. Mobility Lab is about giving consumers additional information so that they can make a truly informed choice.” Counter programming, as it were, to the extremely powerful automobile and oil lobbies.

So there you have it, our dirty little secret: TDM aims to change your behavior, or if not yours, then that of your neighbor. We at Mobility Lab are engaging in TDM every day as we promote some revolutionary concepts: that biking, walking, and using transit can be cool. That living in walkable, urban neighborhoods can be preferable to living in often dehumanizing suburbs, hidden behind fences, interacting with others only at work or the drive-thru fast-food chain.

Hopefully our revolution won’t be that difficult to win. Drivers, when recently surveyed across Virginia, significantly support the concept of TDM – even if they drive alone themselves – because they realize that inducing more people out of their cars means less traffic and a higher quality of life for everyone.

Photos by Marcus Ekelund and Adam Fagan

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