TDM, the Transportation Step Child

by James A. Bacon

There are many ways to reduce traffic congestion — and adding more lane-miles of roads and highways is often the least cost-effective of them. You can shift travel demand from cars to other modes, such as walking, biking, carpooling and transit. You can shift travel to other, less-utilized routes. You can shift travel to less congested periods of the day. And you can eliminate trips altogether by means such as telecommuting. That is the essence of the discipline of Transportation Demand Management.

Now consider: In Fiscal 2012 the commonwealth of Virginia is budgeted to spend $4,760 million building and maintaining the state’s road and highway network, and another $481 million on mass transit and rail — a total of $5,340 million on the supply side of the supply-and-demand equation. By contrast, the state spends a mere $11 million on programs and grants (run by a two-person staff) to manage the demand side of the equation. Of that sum, $7.1 million goes to Arlington County. That leaves about $4 million for the rest of the state.

Put another way, for every dollar Virginia spends on the supply side, one-fifth of one cent is spent on the demand side. What is wrong with this picture?

Economists love transportation demand management (or TDM, as it’s known in the trade). It is often far less expensive to persuade people to abandon their solo, rush-hour commute than it is to add the capacity to accommodate the growing traffic. But TDM doesn’t do much for politicians, who like to brag about building mega-projects that everyone can see and ooh-ah over…. or for career transportation officials, who just  don’t get the same thrill paving up a park ‘n’ ride lot as they do erecting massive steel and concrete structures.

Last month Christopher Arabia, manager of mobility programs, made a presentation to the Commonwealth Transportation Board meeting about the state’s modest TDM initiatives. Board members asked a few questions — just enough to be polite, so the poor fellow didn’t leave thinking that nobody cared — but otherwise showed zero curiosity. Here are some questions they did not ask.

  • Hey, Chris, can you calculate how much traffic congestion your programs relieve?
  • What is the Return on Investment on the state’s investment in TDM — and how does that compare to the Return on Investment in new road and rail projects?
  • Are there any worthwhile programs capable of generating a high ROI that you would like to see funded? If we gave you $50 million a year, what could you do with it?
  • Arlington County arguably has the leading TDM program in the entire country. Are there lessons that other jurisdictions in the state could learn from Arlington?

Alas, none of those questions were asked. I don’t know if Arabia would have had the answers — but Arlington County probably does. A study underwritten by Arlington County Commuter Services in 2009 found that its $7 million program  eliminated 38,000 car trips and 500,000 miles of vehicle travel, saving 23,000 gallons of gas and cutting 255 tons of greenhouse gas emissions every day. Admittedly, Arlington is an urban locale where biking, walking, buses and mass transit are ready alternatives to driving, so its numbers will look better than they would elsewhere. Nobody is suggesting that TDM is the answer. But it is part of the answer. We’re probably under-investing in it, although we can’t know for sure until we start asking the right questions.

Lamentably, transportation in Virginia is all about building more stuff — more highways, more bridges, more rail lines — rather than figuring out how to make better use of the stuff we already have or, better yet, weaving a new urban fabric that is more fiscally and environmentally sustainable in the 21st century. What a shame.