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Forward Motion: Transportation Planning

The Deep Mystery of Traffic Congestion

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Even after sixteen years in the profession, the way transportation planners talk is still a mystery to me sometimes.

Take the acronym “TDM.” It’s actually a fairly old term in the transportation lexicon. But, as slang is wont to do, it has begun journeying to new places in the planning world. Local planners now find themselves being asked by everyone from citizens to elected officials about how they are using TDM to deal with traffic congestion. I daresay more than one has wrinkled a brow and thought, “Now what the heck is that? Traffic Diet Methods? Turnaround During Midtrip? Timed Disruptive Measures?”

Our bewildered planner actually isn’t too far off with any of those guesses. The official term is Transportation (or Travel) Demand Management, but it does involve — albeit a bit loosely — all the strategies mentioned above, and then some.

traffic congestion congestion and gridlock illustrationA typical definition of TDM runs something like this: “Transportation Demand Management (TDM) is a set of planning processes, strategies, and policy decisions that are aimed at relieving congestion and improving efficiencies of the transportation infrastructure.”

Sounds impressive, doesn’t it? Except it doesn’t quite tell me what one does to achieve the aforementioned benefits. Here’s another way of putting it:

Let’s say “Transportation” means “satisfying a need that compels us to go from here to there;” and “Demand” means “the amount we use our roads and paths.” Finally, let’s try defining “Management” as “finding the most efficient way.” TDM would thus mean something like this: “Finding the most efficient way to use our roads and paths in order to satisfy the needs that compel us to go from here to there.”

I’m not sure my language is much more interesting, but it does put the emphasis on the fundamental factor that makes TDM a unique approach to solving congestion. Instead of assuming that ever-increasing traffic is a given and our solution is to engineer more and bigger roads to carry it, a TDM approach asks “What compels us to travel in the first place?” and “What can we do to get those needs met and make the necessary travel more efficient?” It makes us think about the root causes of congestion and find solutions that speak to them.

End of excerpt

photo of Hannah TwaddellHannah Twaddell is President and founder of Twaddell Associates, LLC, a consulting practice specializing in community planning, public engagement, facilitation, and education. Based in Charlottesville, Virginia, the firm provides planning, facilitation, and educational services to communities, government agencies, and private organizations across the U.S.

Before setting up Twaddell Associates, Hannah was a Senior Transportation Planner with Renaissance Planning Group, where she has worked on transportation planning and public involvement projects in several states. Prior to that, she served as Assistant Director of the Thomas Jefferson Planning District Commission (in Charlottesville) and as chief staff to the Charlottesville-Albemarle Metropolitan Planning Organization.

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