Planopedia

Transportation demand management (TDM) describes any of a collection of practices intended to reduce the use of crowded transportation systems by creating new incentives and disincentives for specific kinds of trips. TDM can include policies, programs, and projects, as long as the share the common goal of providing alternatives to a high demand travel mode. In an American context, TDM usually means making mobility options other than a single-occupant automobile trip a more appealing choice, especially during the peak commute hours of the morning and evening.

The same principles of demand management, and reducing the strain of demand, are at work when power companies ask consumers to reduce their use of air conditioners during hot summer months.

Transportation demand management can function as both a congestion relief strategy and an environmental protection strategy, because reducing vehicle miles traveled reduces congestion, pollution, and greenhouse gas emissions.

For congestion relief, transportation demand management is contrasted with the supply-side approach of car-centric planning—expanding the capacity of the transportation system by adding lanes, reducing obstacles, or improving technology. However, added capacity can create new demand for the system—a phenomenon known as induced demand. TDM, however, provides an alternative to the supply-side approach. Without altering the system itself, TDM can improve the performance of transportation systems by removing the demand stress. 

Sometimes adding capacity can be construed as a TDM strategy—for example, by adding capacity to the public  transit system, demand for the nearby automobile infrastructure can be reduced. Added capacity on a transit system, either with new lines added by capital investments or improved operation and maintenance, provide reasonable and attractive alternatives to automobile trips (although the effects of improved public transit on congestion is still a matter of debate).

Changing Definitions and Purposes

In the past, TDM was narrowly defined, with a few specific examples, such as commuter ridesharing, reserved for air pollution mitigation (especially as required by federal and state environmental regulations) or the environmental analysis required of new development (both for setting parking requirements and for calculating the trip generation rates and Level of Service created by developments). In the past, TDM applications were limited primarily to a focus on the mode choice of office workers traveling by car in and out of the central business district of cities and regions at peak hours during the morning and evening. 

In addition to commuter mode choice, contemporary TDM also addresses travel routes, departure times, and origin and destination choices, among other trip reduction strategies. The definition has shifted as planners have adopted a more holistic approach to TDM, recognizing the benefits of trip reductions for multiple systems, at varied times of the day, and for a larger and more diverse number of individuals.

Integration in Planning Processes

Given its broad application in a number of transportation systems, TDM is a common tool of both transportation and environmental planning by planners and regulators at the local, regional, and national levels. Planners will rely on TDM as an implementation tool whenever they set goals for reducing VMT, particulate emissions, and congestion.

TDM frequently requires creative public-private partnerships. For example, the public sector can provide financial support or tax breaks to companies to provide transit passes, restrict parking, or allow flexible work schedules that allow for commuting before or after the morning and evening rush hours. 

The Federal Highway Administration, part of the U.S. Department of Transportation, is most involved with TDM at the federal level, funding programs and engineering federally-owned roads. State regulators, metropolitan planning organizations, regional governments, and local governments are arguably most visible in their use of TDM as a tool for congestion relief and pollution mitigation.  

Transportation Demand Management Examples

TDM applications are varied and diverse. Here are just some of the examples of TDM as applied around the country and world:

• Carpool Incentives
• Free or Subsidized Transit Passes
• Free or Subsidized Bikeshare Programs
• Parking Opt-Out Programs
• Parking Demand Management
• Parking Requirement Reform
• Transit Oriented Development
• Mixed-Use Development
• Bike Parking 
• Congestion Pricing
• Cordon Pricing
• Tolls
• Telecommuting Programs
• Bike and Pedestrian Infrastructure
• Transit Operations
• Transit Capital Improvements
• Shuttle Services
• Promotional Events (e.g., Bike to Work Week)
• Ridesharing Programs 
• First-Last Mile Programs and Projects
• Flexible Work Hours
• Off-Peak Commuting Incentives
• Wayfinding
• Vehicle Use Restrictions
• Traffic Calming
• Point Systems
• Fuel Taxes
• Vehicle Fees

Planners and engineers will likely continue to develop new TDM practices as a response to persistent congestion and pollution in an evolving economy.