Transportation Demand Management
A variety of Transportation Demand Management (TDM) strategies can be used to influence the demand for vehicular travel in any medium or large sized urban area. TDM strategies focus primarily on encouraging different forms of commute travel and alternative work arrangements. Although comprising slightly less than 20 percent of all vehicular trips in the average urban area, commute trips generally cluster around the most congested peak periods and involve static origins, destinations, and times of arrival at / departure from work. These factors make commute trips particularly susceptible for adaptation of travel by various modes, including carpooling, vanpooling, public transit, bicycling, and walking – the core “alternative modes” of TDM. Furthermore, alternative work arrangements – including flex-time, compressed work weeks, and teleworking – provide another means of shifting trips out of the peak periods without shifting modes.
Over fifty discrete types of TDM strategies and activities have been deployed by communities throughout the United States and Canada, to varying levels of success. Most strategies employ some level of awareness and marketing of commute travel alternatives. A majority of strategies provide incentives for the use of alternatives – either infrastructural (e.g., HOV lanes, preferential parking spaces, and bicycle racks) or financial (e.g., reduced fuel prices for carpoolers, pre-tax set-asides for vanpool and transit fares). Only a few strategies use punitive measures to affect demand (e.g., parking or road pricing). Overall, the various types of strategies can be aggregated into three general classifications of strategies. These classifications demonstrate both the intensity of application and resource commitment needed to affect these strategies.
The three levels are defined as:
The evaluation of impacts from TDM strategies tends to reflect the purpose behind their primary funding sources. Exclusively basic-level TDM programs are primarily found in communities who attain air quality targets as established by the U.S. Environmental Protection Agency. These communities tend to use TDM programs for congestion avoidance and access-to-work purposes, and fund them through various sources, including the Surface Transportation Program (STP). The collective impact of basic-level TDM strategies upon travel times, vehicle miles traveled, and other regional performance measures are generally marginal, and often are overwhelmed by ambient non-commute traffic growth.
By comparison, moderate TDM strategies are most often found in communities who are in non-attainment with air quality goals. Funded substantially through the Congestion Mitigation / Air Quality (CMAQ) program, moderate-level TDM strategies are most often evaluated against air quality measures – primarily vehicle trip, vehicle miles traveled, and pounds of pollutant reduction. Virtually no program endeavors to measure the discrete effects of TDM upon travel times and other transportation network performance.
Case Study: Cash for Commuters Program (Atlanta, Georgia; 2002 – 2004)
Source: Center for Transportation and the Environment. The Clean Air Campaign Cash for Commuters Program: Final Report, Georgia Department of Transportation / Federal Highway Administration, November 2004.
Funded from Atlanta’s Congestion Mitigation / Air Quality (CMAQ) program, the Clean Air Campaign conducted an ambitious “moderate” TDM strategy involving the payment of cash incentives to single-occupant vehicle commuters who switched to a modal alternative. Conducted in three waves between 2002 and 2004, approximately 8,500 regional commuters enrolled in the program (with 5,500 completing the program and receiving their incentives). Participants earned up to $60 per month (for three months) by choosing and using an eligible alternative mode of transportation.
Evaluation efforts examined the effectiveness of the program both during and after termination of incentive. Prior to receiving incentive from the program, participants used commute alternatives an average of 0.75 days per week. During the program, participants’ utilization jumped to 4.30 days per week. Finally, 18-21 months after completing the program, participants used commute alternatives an average of 2.35 days per week. Overall, program participants almost halved their single-occupant vehicle commute utilization 18-21 months after completion of the program – from 84 percent drive alone to 53 percent. This translated to an average impact of 1,057 vehicle trips per day and 25,791 vehicle miles traveled per day reduction, with over 512,000 total vehicle trips and over 12.5 million vehicle miles traveled reduced over the life of the program.
Over fifty discrete types of TDM strategies and activities have been deployed by communities throughout the United States and Canada, to varying levels of success. Most strategies employ some level of awareness and marketing of commute travel alternatives. A majority of strategies provide incentives for the use of alternatives – either infrastructural (e.g., HOV lanes, preferential parking spaces, and bicycle racks) or financial (e.g., reduced fuel prices for carpoolers, pre-tax set-asides for vanpool and transit fares). Only a few strategies use punitive measures to affect demand (e.g., parking or road pricing). Overall, the various types of strategies can be aggregated into three general classifications of strategies. These classifications demonstrate both the intensity of application and resource commitment needed to affect these strategies.
The three levels are defined as:
- Basic – administered in most medium and large urban areas, basic TDM strategies generally use existing financial and staff resources to implement marketing, promotion, and ridesharing services. Typical basic strategies include operating a regional ridematch service, provision of vanpools, and awareness campaigns conducted through large regional employers. A package of basic TDM strategies may hope to shift up to two percent of single-occupant vehicle commuters to other modes at participating worksites.
- Moderate – moderate strategies often involve inventive and/or resource intensive implementations of basic strategies. Generally, moderate strategies tend to be those that are accomplished within existing statutory guidance, but require a formal commitment of resources and mindset to demand management, which in turn, may spill into other governmental realms (such as development review, environmental enforcement, and other services). These strategies may include incentives to developers to provide for on-site infrastructure and services conducive to bicycling and transit, small financial incentives to carpoolers, empty-seat subsidies to vanpools, and discounted monthly / annual transit passes. Moderate strategies may achieve up to a seven percent shift of single-occupant vehicle commuters to other modes at participating worksites.
- Aggressive – aggressive strategies move beyond the current experiences from around the country to create advanced levels of implementation. In some cases, concepts may be experimental or require new statutory authorization (e.g., the proposed congestion pricing program for Manhattan). In other cases, aggressive strategies would look to re-implement a regulatory environment for commute alternatives, such as those employed in California in the 1980s. Aggressive strategies may also require a realignment of transportation infrastructure expenditure priorities from general-purpose roadway capacity to targeted multi-modal corridors and services. Many emerging technologies, including active traffic management, bus rapid transit, and managed lanes, serve this multi-modal corridor perspective. Aggressive strategies may achieve significant (over 30 percent) reductions in single-occupant vehicle commuters at participating worksites (as witnessed at regulated employers in California) as well as shifts in non-commute modes of travel. However, it should be noted, that aggressive TDM efforts are limited and proven effectiveness is generally theoretical.
The evaluation of impacts from TDM strategies tends to reflect the purpose behind their primary funding sources. Exclusively basic-level TDM programs are primarily found in communities who attain air quality targets as established by the U.S. Environmental Protection Agency. These communities tend to use TDM programs for congestion avoidance and access-to-work purposes, and fund them through various sources, including the Surface Transportation Program (STP). The collective impact of basic-level TDM strategies upon travel times, vehicle miles traveled, and other regional performance measures are generally marginal, and often are overwhelmed by ambient non-commute traffic growth.
By comparison, moderate TDM strategies are most often found in communities who are in non-attainment with air quality goals. Funded substantially through the Congestion Mitigation / Air Quality (CMAQ) program, moderate-level TDM strategies are most often evaluated against air quality measures – primarily vehicle trip, vehicle miles traveled, and pounds of pollutant reduction. Virtually no program endeavors to measure the discrete effects of TDM upon travel times and other transportation network performance.
Case Study: Cash for Commuters Program (Atlanta, Georgia; 2002 – 2004)
Source: Center for Transportation and the Environment. The Clean Air Campaign Cash for Commuters Program: Final Report, Georgia Department of Transportation / Federal Highway Administration, November 2004.
Funded from Atlanta’s Congestion Mitigation / Air Quality (CMAQ) program, the Clean Air Campaign conducted an ambitious “moderate” TDM strategy involving the payment of cash incentives to single-occupant vehicle commuters who switched to a modal alternative. Conducted in three waves between 2002 and 2004, approximately 8,500 regional commuters enrolled in the program (with 5,500 completing the program and receiving their incentives). Participants earned up to $60 per month (for three months) by choosing and using an eligible alternative mode of transportation.
Evaluation efforts examined the effectiveness of the program both during and after termination of incentive. Prior to receiving incentive from the program, participants used commute alternatives an average of 0.75 days per week. During the program, participants’ utilization jumped to 4.30 days per week. Finally, 18-21 months after completing the program, participants used commute alternatives an average of 2.35 days per week. Overall, program participants almost halved their single-occupant vehicle commute utilization 18-21 months after completion of the program – from 84 percent drive alone to 53 percent. This translated to an average impact of 1,057 vehicle trips per day and 25,791 vehicle miles traveled per day reduction, with over 512,000 total vehicle trips and over 12.5 million vehicle miles traveled reduced over the life of the program.
