Practical Applications of Transportation Demand Management

Transportation demand management (TDM) programs have been around as major components of urban transportation systems since the 1970s and a significant body of knowledge has been built over this time. In practice, TDM programs range from light-duty marketing campaigns that accomplish little to robust, integrated systems that have measurable impacts on traffic volumes in specific corridors or districts.

Scale and Integration

One of the keys to successful TDM programs is understanding how to manage the scale of TDM programs and how to work within a complex urban environment with multiple agencies and organizations interacting, sometimes with competing goals.

Different TDM measures are appropriate for implementation by different entities at different scales. There is little a single employer can do to improve regional public transit service, for example. Regional transit agencies with regional tax bases provide transit service and they typically participate in ancillary programs designed to promote transit patronage, including setting up pass programs. Cities within those transit regions may be represented on the transit board and can influence transit decision making. In some cases, cities may operate local circulators and shuttles as adjuncts to the regional transit system. Groups of employers, operating through a Transportation Management Association (TMA), can implement an employee transit pass program, sharing costs and creating an efficient marketing effort with an information clearinghouse. They can work with the transit agency and city to obtain better service or improved transit stops near their worksites, or to run a local circulator. In many cases, the state department of transportation or a metropolitan planning organization (MPO) may have funds available to help start up TMAs and to support their efforts. In fact, many metropolitan areas have a regional commute trip reduction program designed to provide services and resources to TMAs.

Successful deployment of a regional transit system to reduce driving by commuters entails vertical integration and cooperation among these different entities. This principle applies not just to transit, but to other kinds of TDM systems and services. In design of any type of TDM program, it is important to map out vertical and horizontal relationships and to target resources strategically to those measures that realistically fall within the influence of the implementing entity. This requires collaboration and coordination among private companies and public entities. It also benefits from open communication. While there are many reasons why private employers can and should compete with each other, TDM programs are inherently cooperative in nature. Success requires that the entities involved work together to build the scale of effort required to achieve measurable results.

So, what a single employer can do is: help form a TMA, participate actively in that TMA, lobby the city and transit agency for better transit service and other support, and then work to ensure that employees are aware of their transit options and have ready access to transit passes and other program features, perhaps by implementing a parking cash-out or transportation allowance as part of an employee benefits package.

Measurement and Reporting of Results

TDM programs cost money that could be invested in other things. To ensure that programs have continued support, whether from public boards and elected bodies or from the managers of private companies, it is essential to describe program objectives and expectations in measurable terms and then to monitor and report outcomes.

Most successful TDM programs have well-structured systems of objectives and performance measures that are reported monthly, quarterly, and annually. The best monitoring systems include outcomes (such as trips reduced) as well as diagnostic information (such as percent of employees with transit passes). These data, coupled with cost reporting and a frank assessment of program performance, enable program managers to improve the program steadily and also ensure continued support for the required investment from management.

Measurement and reporting systems for TDM programs vary widely, but common elements of most programs report results using such measures as:

  • Average weekday transit ridership
  • Mode share (percent of trips made by driving alone, carpooling, transit, walking, bicycling)
  • Traffic levels in specific corridors, at entrances to work-sites, or across cordon lines
  • Number of participants signed up for parking cash-out or transportation allowances
  • Peak observed parking demand
  • Various financial measures of program costs and revenues

The most common measure of TDM results is stated in terms of vehicle trip reduction. This is useful because it focuses directly on what is normally the most important objective--managing traffic congestion. To measure and report vehicle trip reduction, it is necessary to set a benchmark or baseline that is based on actual measurement of the current situation or status quo. This normally includes counting vehicles at preset locations and surveying employees or other travelers to determine travel behavior.

In setting objectives, scale is important. A 40 percent transit mode share for commute trips into a downtown or major employment center is achievable assuming good transit service coupled with a smart TDM program. However, for all trip purposes citywide a 4 percent transit mode share would be considered high in most U.S. cities. Large office parks with good transit service and congested highways--say, in San Francisco or Seattle--have achieved commute trip reductions of as much as 55 percent to 60 percent. But a high percentage of employment in most regions works in small companies where TDM programs may be less effective, so regional commute trip reductions, even with highly successful programs, are generally less than 10 percent.

Generally, it makes sense to set modest objectives and to design an initial program that integrates multiple TDM measures to achieve those objectives. Then, following annual reporting and analysis, the implementing entity should focus in on those strategies that appear to be working and also diagnose why others are not working. Over time a good TDM program is a learning system that improves and becomes more efficient.

TDM programs are generally designed to “reduce traffic” or “manage congestion.” Measuring their actual performance toward these objectives must take into account the fact that what these programs do is build on the performance of other programs.

Take, for example, a company that provides transit passes and offers an employee transportation allowance program designed to encourage transit ridership. This employer program is making use of transit investments made by others. In this case, there may already have been some transit ridership before the company instituted the program and the actual impact of the program would be to increase the amount of transit ridership. Measuring the performance of this program would require establishing a baseline measurement prior to program implementation so that the amount of change could be measured. It would also be important to acknowledge that many other factors could also be changing during the measurement period, such as the level of transit service being provided, the price of gasoline and so forth. Good measurement systems would explicitly note and document these other factors and their likely effects.

Measurement and reporting systems may focus on a specific type of travel. For example employers will measure “commute trips” to and from their worksite. Cities may measure all daily travel by residents, or all commute travel by people employed within their city. Downtowns and other activity centers may measure travel behavior by trip purpose, separating work trips from shopping trips. Potential outcomes for different potential frames of measurement are summarized below.

Employers. In urban regions where good transit service is available directly to the worksite, arterial streets are congested during peak hours, and walking and bicycling are safe and convenient, large employers can sometimes show commute trip reductions (reduced auto trips by employees) above 50 percent. By contrast, small employers in suburban locations with little transit service and poor walking and bicycling environments would have to rely entirely on carpools and might succeed in reducing commute auto trips by only a few percentage points. Table 1 shows the commute trip reduction objectives that the Seattle region’s Commute Trip Reduction (CTR) program has set for large employers (over 100 employees). The program sets objectives to be reached within a set number of years following company formation or after otherwise qualifying under the CTR regulations.

Office Park or TMA. Office parks or groups of employers within a defined geographic area often work through a TMA to achieve results similar to those shown in the table above. However, in many urban regions the results at this level would be more modest, with many TMAs reporting commute trip reductions in the 10 percent to 25 percent range.

Municipality. Some cities around the United States have set trip reduction or similar objectives and are monitoring and measuring their progress. One of the earliest cities to adopt a citywide TDM program was the City of Boulder, Colorado, which established its “GO Boulder” (Great Options) program in 1990. Boulder’s population today is just over 100,000, which is a manageable size for such a program--large enough to deploy a sophisticated demand management effort, but small enough to have meaningful city-wide TDM program administration. Data from Boulder’s monitoring program is shown in Tables 2 and 3.

Table 2 provides data for residents of the city and all trip purposes, using the common “mode share” measurement based on a resident travel diary administered as a random sample survey. Table 3 provides data for the commute travel behavior of people who hold jobs in Boulder, some of whom live outside the city.

Boulder is an unusual place; these results might not be achievable in many cities. The high walk/bike mode share shown in Table 2 (32.5 percent in 2006) reflects the City’s investments in walking and biking infrastructure, but also reflects the presence of the University of Colorado campus with almost 30,000 students attending classes.

The remarkable increases in transit mode share--both for resident trips and for work commutes--resulted from an ambitious expansion of transit service funded in part by the City through its Community Transit Network, which augments the services of the Regional Transportation District (RTD) with local, high-frequency bus routes. Probably the most important TDM measure initiated by the City (in coordination with RTD) is the Eco Pass program which provides discounted transit passes to companies that opt into the Eco Pass program.

Boulder’s total non-single-occupancy-vehicle mode shares shown in Tables 2 and 3 represent performance that is near the upper end of what can be achieved in a U.S. city today.
The City of Portland, Oregon has established objectives for bicycle mode share as part of a city-wide effort to “make bicycle ridership a part of daily life in Portland.” Although the City does not conduct a comprehensive survey like Boulder, Portland does undertake a “Bicycle Count” program that is calibrated against U.S. Census data. Portland’s bike mode share objectives are shown in Table 4. As of 2008 the City believed it was on track to achieve the 2011 objectives. If it succeeds, this will set a new standard for bicycling in an American city.

Region. Most urban regions have significant transportation demand management programs designed to provide support to cities, TMAs, employers and commuters. These regional programs are often housed at a Metropolitan Planning Organization (MPO) or a Regional Planning Council (RPC). Many MPOs and RPCs conduct periodic travel behavior research projects to monitor personal travel in their regions. Typical reporting measures would include per capita daily vehicle miles of travel, single occupant vehicle mode share for commute travel (also available every ten years from Census data packages), and transit mode share. Table 5 provides data for the Seattle region published by the Puget Sound Regional Council.

Program Duration and Lifecycle

TDM programs are inherently operational in nature. They require continuing effort and long term commitment. If a TDM program is deemphasized or loses management focus, even for a short period of time, program performance will suffer measurable declines.

The durability of TDM programs is also affected by the changing cast of people involved in the programs. Even the most stable companies have employee turnover, including in the ranks of the people administering the TDM program. TMA employees also come and go. Elected leadership in most cities changes over time, which affects not just who holds office but also what policies are considered important and what programs are funded. Finally, actual program participants--the carpoolers, transit riders, and so forth--change jobs and housing frequently. For example, the average life of a carpool in some markets may be less than a year.

Consequently, a primary challenge in running a successful TDM program is maintaining satisfactory performance in the face of changing personnel, shifting priorities, and organizational inertia. At the scale of individual employers or office parks it is common for performance to peak after two to four years of effort and then to go into decline as priorities and attention are focused elsewhere. At the local or regional scale, policies and priorities migrate over time to new programs and new ideas sometimes leaving established TDM programs in their wake. For these reasons, transportation officials at all levels of government tend to be skeptical of the prospects for TDM programs to play a permanent or significant role in alleviating traffic or managing congestion.

Thus, an important design feature of any successful TDM program is the institution of long-term commitments and requirements that bind future agencies, employers, property owners and others to continued investment and active participation in the program.

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