TRANSPORTATION DEMAND MANAGEMENT
TDM, also referred to as “Traffic Demand Management” or “Travel Demand Management,” is a set of planning policies and strategies aimed at changing travel behaviors, particularly in heavily-traveled urbanized areas.
TDM precepts arose from the realization that the costs to build sufficient transportation infrastructure supply were financially and environmentally unsustainable.
Rather than respond in a reactive manner to increase supply of such things as roads, bridges and parking facilities, planners are adopting TDM principles to proactively reduce the demand side of the transportation equation. TDM advocates claim that reducing transportation demand equates to increasing supply saving time, money and environmental impact.
TDM principles promise to improve the overall efficiency of transportation ecosystems.
The Mobility Lab, a unique joint venture of city, state and federal government agencies formed to address congestion in the suburbs of Washington, D.C., puts it this way:
“Transportation demand management is the flip side of infrastructure. It focuses on helping people use the infrastructure in place for transit, ridesharing, walking, biking, and telework. It is cost-effective in guiding the design of our transportation and physical infrastructure so that alternatives to driving are naturally encouraged and our systems are better balanced.” (https://mobilitylab.org/about-us/what-is-tdm/)
Why is TDM Important?
The “default” choice of transportation mode for many people when considering their personal cost, time, convenience and comfort is the Single-Occupant Vehicle (SOV).
TDM seeks to educate the public about the impacts of the SOV on the economy, society and the environment. By enhancing non-SOV transportation options, TDM aims to change this mindset.
At H2, our goal is to make these alternative modes of travel more competitive, desirable and sustainable.
Research has shown that SOV use has been subsidized over the last century by government legislation and regulatory practices. These laws and practices, such as toll-free highways and requiring a minimum parking supply for all new development, have contributed to an unbalanced transportation grid. The enormous cost of building an ever-increasing supply of highway infrastructure to address this sprawl was spread over all of society, rather than being focused solely on road users. TDM guidelines seek to reverse these subsidies and what their advocates claim is preferential treatment for SOVs. TDM aims to reassign transportation costs to more fairly represent the true costs to society and the economy of driving vis-á-vis other alternatives.
There are other societal impacts created by traffic that need to be managed. The SOV, cruising under ideal, light-traffic circumstances, is perhaps the most comfortable and convenient mode of personal transportation, but it is also a contributing factor to congestion, sprawl and urban blight. TDM principles are community-centered and seek to encourage walkable, mixed-use neighborhoods. A TDM professional works within a community to help make that happen.
Finally, the effects of traffic on the environment must be managed. Transportation infrastructure requires manufacturing massive amounts of concrete and steel. These processes disproportionately consume natural resources and emit pollution. Studies have shown impermeable asphalt and concrete parking facilities are by far the largest land use in urban areas, creating “heat islands” and causing polluted stormwater runoff. Traffic contributes excess carbon dioxide and toxic particulates into the atmosphere. These environmental effects must be eliminated where possible but mitigated everywhere. Again, a community-based TDM practitioner is the fulcrum of this effort.
A Balanced Approach to TDM
While many TDM programs only target the reduction in the use of the SOV as a travel mode, we at the H2H2H Foundation take a slightly different approach. We believe TDM is about achieving a balance in the use of the available transport modes calibrated at a local level.
While modes such as public transit are well developed in certain areas, in other locales penalizing private vehicle use without viable – and acceptable – alternatives will create more problems than they solve. What is needed is for hands-on professionals on the ground in their communities to evaluate TDM options and create a menu of solutions unique to that neighborhood, campus or destination.
These solutions must be integrated with the transportation infrastructure already in place, including roadways, intermodal facilities and parking lots. But, TDM operations must be practical and reality-based. Travel patterns will never be changed by advocacy programs and demonizing private vehicle usage alone. Alternatives to the SOV must be enhanced and improved so travelers choose them because they offer benefits and value.
Enter good management. For these reasons, a professional “TDM Manager” is, or should be, rebranded a “Mobility Manager.”