To Define TDM, Follow the Money? - TransitCenter
June 13, 2014
To Define TDM, Follow the Money?

In places with strong sustainable transportation networks, TDM can be a powerful tool to increase use of those networks. | Source: Steven Vance.

TDM practitioners are selling themselves short.

For the uninitiated, Transportation Demand Management, or TDM encompasses a range of strategies and policies to influence travel behavior to improve mobility and increases everyone’s access to jobs, businesses, parks, and schools. From charging for parking, building bike lanes, providing travel information and resources, to financial incentives for carpooling to work, these actions help everyone to their destination that is less expensive and with less of an impact on the environment.

Implemented at a range of levels, from states, regions, all the way down to individual worksites and even Yosemite National Park, TDM strategies have proven successful at boosting transit use, ridesharing, biking and walking.

The field fascinates us at TransitCenter due to its unique nature of straddling the public and private sector, and the variation in its implementation across the United States. Influencing how people travel interests a range of stakeholders who carry out these strategies for a variety of different reasons.  There is no one agreed upon definition for TDM leaving its many practitioners to define it for themselves.

Reviewing these definitions, I found that many public sector practitioners view TDM in a very narrow sense. Take for example these definitions of TDM from a state DOT and regional MPO:

“Programs and methods to reduce effective demand… The highest priority in the region is given to reducing single-occupant vehicle trips in the peak periods. ” — Minnesota DOT

“…activities that help people use the transportation system more efficiently, while reducing traffic congestion, vehicle emissions and fuel consumption.” — Denver Regional Council of Governments

This pattern holds up across many states and regions: TDM is seen as a tool to cut car use and congestion. Worthy causes, of course, but TDM has other benefits: By making it easier for people to use sustainable transportation, it can support a region’s economic development and improve public health. Why do most public sector definitions of TDM ignore these benefits?

Well, most public sector definitions are strikingly similar to the description of eligible projects for federal Congestion Mitigation and Air Quality, or CMAQ, funds. They are described by the Federal Highway Administration as:

“Projects that shift traffic demand to nonpeak hours or other transportation modes, increase vehicle occupancy rates, or otherwise reduce demand.”

Which makes perfect sense when you follow the money.  The Center for Transportation and the Environment surveyed 9 regional TDM programs and found nearly 60% of their funding originates from CMAQ grants.


Source: Center for Transportation and the Environment, 2006.

Whether public sector TDM programs are consciously defining their work around their primary funding source or not is intriguing. But municipalities and researchers are starting to broaden their funding sources and definitions to reposition their TDM work.

In its Transportation Master Plan, the City of Redmond, Washington (full disclosure: A former employer of mine), which funds a TDM program through a business tax, describes its approach to TDM as

“Tools, resources, programs, and partnerships to improve access and mobility to support economic growth and community character and make alternative travel choices easier to use and access.”

That’s a very different vision of what TDM should do! No mention of system efficiency. No mention of reducing car use. When your program is instead funded by businesses and less from sources dedicated to congestion mitigation and air quality, it shows in the definition.

Public sector definitions do not have to just follow the funding. By leaving out these comprehensive benefits, TDM practitioners are selling their work short and leaving potential funds on the table.  If public sector practitioners redefined their TDM programs, with a focus on economic development, public health, and social equity, they might open the door to more diverse funding sources and make their work more relevant to more people.

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