Tables

For the past forty years immigration of population from rural areas to urban areas throughout the country resulted in concentration of population in metropolitan areas and urbanization of surrounding areas. To coordinate the urban development, the local governments implemented the urban development plan. Many metropolitan areas experienced steadily increasing traffics around the areas, mainly due to commuting from the suburbs to the central business district. As an important component of the urban development plan, the metropolitan area governments set up MPOs to develop and implement the transportation plan to solve the problem of traffic congestion and resulting negative impact on the locals such as traffic accidents and pollution. Initially, the MPOs responded to these problems by developing plans to increase the network and capacity of highways across urban areas. In the 1970s, facing an oil embargo and sudden increase in energy prices the U.S. Department of Transportation initiated a study to increase the use of public transportation. This was a watershed of transportation planning in the U.S. This policy called for discouraging people driving to work, and was the first Transportation demand management (TDM) in the U.S.

TDM, also called transport demand management, travel demand management or congestion management, is a set of procedures that make efficient use of current highway network and capacity. It is intended to reduce traffic during peak hours through alleviating the unlimited use of the automobile, increasing the average vehicle occupancy, shifting travel from peak hours, diverting traffic from congested areas, and encouraging the use of public transportation. Until recently, TDM has been implemented mainly in large urban centers such as Los Angeles, New York, Washington, D.C., and Atlanta. However, shifting businesses and population from large urban centers to medium-size metropolitan areas, such as Charlotte, Raleigh-Durham-Chapel Hill (Research Triangle), and Greensboro-Winston-Salem-High Point (Piedmont Triad) in North Carolina, lead these areas more traffic congestion than ever. Until now, these medium-size metropolitan areas mainly responded by constructing new highways and resulted in a limited use of TDM.

Most medium-size metropolitan areas, as compared with larger metropolitan areas, do not have extensive highway network or public transportation throughout the areas. Their populations rapidly increase, so their suburban areas extend out from the center of the area. Although the business and industrial development is carefully planned, residential areas are developed and clustered throughout the areas, and commercial development comes along major highways and streets. Often, these medium-sized metropolitan areas have more than one central business districts, such as the Research Triangle and the Piedmont Triad. Many of new comers are dual-career families, in which a husband and a wife may commute to different locations. As a result, there are high traffic flows between two or more central districts within the metropolitan area. In addition, most of these medium-sized metropolitan areas are along major Interstate Highways between two larger metropolitan areas, i.e. Piedmont Triad and Charlotte are located between Washington, D.C. and Atlanta, so there are a high level of through-traffic, both commercial and private. These unique characteristics of medium-size metropolitan areas call for different sets of TDM measures. Those measures often used in larger metropolitan areas may not be feasible, effective, or acceptable by the public in the medium-size metropolitan areas.

The objective of this study is threefold; to identify the current implementation of the TDM measures, to evaluate an effectiveness of each TDM measure, and to compare with the cost of implementing these TDM measures in the medium-size metropolitan areas.

Although the TDM has been around for thirty years, its implementation has been limited mostly in large metropolitan areas and a few medium-size metropolitan areas that have integrated a comprehensive TDM strategy into its transportation plan. However, some local governments in medium-size metropolitan areas, which respond to traffic problems mainly by expanding the network and capacity of highways, began considering alternative strategies to solve ever-increasing traffic problems on highways. For example, both the Research Triangle and Charlotte in North Carolina recently started TDM feasibility studies. With renewed attention mainly from medium-sized metropolitan areas, first it is important to understand current implementation of TDM not only in large-sized metropolitan areas, but also in medium-sized metropolitan areas. A nationwide survey can reveal what kind of traffic problems each metropolitan area faces and how they implement the TDM to solve those problems.

Second, this study evaluates the effectiveness of those implemented TDM measures. The effectiveness of a TDM measure can be measured in various dimensions, i.e. specific changes in travel behavior of commuters such as shift of peak-hour travel to off-peak hour and shifting away from congested areas, a reduction in overall congestion, and a reduction in air pollution. Of course, the effectiveness of each TDM measure depends on the current level of implementation of each TDM measure and other factors such as current traffic conditions and networks of highways in the area. Thus, the effectiveness of TDM measures in each area is evaluated in conjunction with these factors.

Third, this study evaluates costs associated with implementing TDM measures. Costs of implementing TDM measure include the initial capital expenditure, annual operating costs, and non-monetary costs to local residents near the congested areas targeted by a particular TDM measure. Although the TDM is a cost-saving alternative to expanding highways to solve the traffic problem, its monetary cost may vary from one TDM measure to another. Non-monetary costs are often borne by residents nearby the highway where the TDM measure is implemented, including increased accident and traffic problem on local streets and noise/air pollution.

It is important to note that the effectiveness and cost of TDM measures can be evaluated only with the understanding of current level of implementation of the TDM measures. Also, with a standardized survey, a nationwide study permits us to draw an overall picture of the TDM implementation in the nation and to compare directly one area with another.

Previous studies in the transportation demand management mainly focused in the transportation demand management (TDM) implemented in large metropolitan areas. Some studies looked at a particular metropolitan area and evaluated the effectiveness of each TDM measures. Others reviewed various area-specific studies and tried to identify a general pattern of results. Because each area-specific study was done differently, the later studies were more qualitative assessment of the TDM measures and did not take into account specific characteristics of each metropolitan area. Quite a few medium-size metropolitan areas and no small-size metropolitan areas were studied.

A web-based questionnaire was developed to assess the effectiveness and cost of TDM measures. Because this study focuses on various TDM measures implemented in many different metropolitan areas, a traveler survey is not feasible. Instead, MPOs, which set and implement area transportation plans and collect various local informations on traffic condition and travelers behavior, are expected to have much of this information. Because of their expertise, their responses are expected to be more standardized and more objective. Thus, the MPOs throughout the nation were invited to participate the survey. All sizes of metropolitan areas are surveyed for comparison purpose.

The estimated model can not only identify effective TDM measures in medium-size metropolitan areas, but is also used to predict the effect of TDM measures in areas that have not implemented some or any TDM measures at all. Because factors affecting effectiveness and cost of TDM measures are modeled, the model can predict the effectiveness and cost of TDM measures at a particular metropolitan area, given the characteristics of the metropolitan area. By measuring the effectiveness and cost of each TDM measures in conjunction with the current level of implementation, the study can provide a rough cost-benefit analysis of TDM measures. In addition, the study can predict an equity effect of TDM measures, which may be more important in some metropolitan areas such as those in South.

TDM is used extensively in Europe where there is wider agreement that the use of the automobile must be restrained to preserve the urban environment. Saleh and Bell (1997) present a comprehensive summary of TDM projects in Europe. They classify TDM into Main Measures and Complementary Measures. The authors conclude that packages of TDM elementary measures be constructed out of one or more main measures and one or more complementary measures for maximum impact (e.g. V1008 Consortium, 1989; Jones, 1991; Oda, 1990; DOT, 1994 and Saint-Laurent et al, 1994). Saleh and Bell also suggest criteria for evaluation of TDM measures that include demand impacts, network impacts and environmental impacts.

TDM is also used in the United States to a lesser extent and many of them are in large metropolitan areas such as Los Angels, Washington, D.C., and Seattle. Although there are some small examples of its use in the Piedmont Triad and North Carolina in general, there is no effort to use a comprehensive TDM program in the mid-size metropolitan areas in the southeast. Some recent applications of TDM in the United States include parking restrictions (Bradley, 1996), employer based programs (Higgins, 1996), HOV lanes (Paiewonsky, 1997, Best, 1997 and Fedrick, 1997) and traffic light preemption for public transit (Khasnabis and Rudraraju, 1997).

An extensive effort that summarizes the use of TDM in metropolitan areas is presented by Saleh and Bell (1997). They consider a wide range of options both one at a time and all together. For this report travel demand management and transportation demand management are considered to be the same concept. They point out that the TDM strategies depend on the goals to be achieved. These goals may be to:

a. reduce congestion

b. reduce pollution

c. reduce energy consumption and

d. improve safety.

There are also several strategies to achieve these goals which include:

a. reduce vehicle miles,

b. reduce temporal peaks of car demand and

c. reduce spatial concentration of car demand.

There are several types of transportation demand management which are applied as different tools to achieve the various goals.

The first type of measures is innovative supply. These include the following:

1. Park and ride lots for public transportation

2. Car-pool or vanpool programs that can reduce the number of vehicle miles by increasing the number of passengers per vehicle. These programs usually use computer match programs that find people who are leaving similar origins for similar destinations. Dial-a-ride can enable pick up and delivery of passengers and is especially used for elderly and disabled passengers.

3. Traveler information service which is used to give commuters the best route to work. i. Variable message signs give information en route

ii. In-vehicle message units give shortest routes to individual commuters

iii. Home message units give on-line information before trips are started.

The second type of TDM measure is pricing measures. These include the following:

1. Paying a toll to use the highway or other surface transportation facility (e.g. a bridge of tunnel) during rush hour for all users. This form of congestion pricing will apply to everyone.

2. Decarlo-Souza (2000) points out that tolls may be combined with HOV lanes to form high occupancy toll (HOT) lanes. In these lanes extra passengers are not required if a toll is paid. This toll may change during the day depending on traffic volume so that it acts as a congestion price.

3. Decarlo-Souza (2000) also discusses parking pricing.

4. Parking discounts to car poolers or others who travel to work in a prescribed manner.

The third type is various TDM regulation measures including

1. High occupancy vehicle lanes (HOV) are priority lanes on the highway for cars with extra passengers.

2. Priority reserved parking spaces at the destination (e.g. work) for people who take 2 or more passengers or who pay a toll.

3. Employers can provide free transit passes to their employees. There is provision in current federal legislation to give employers incentives to provide this type of program.

4. Programs to encourage tele-commuting to work or (possibly) other activities. Working at home some days each week can also reduce the cost of travel.

5. Flexible work hours (flextime) reduces congestion during the rush hour by having people travel at different times.

6. Compressed workweek (work four days or less each week) reduces the number of commute trips.

7. Auto restricted zones at certain times of the day.

Complementary measures consist of measures that are combined in packages to make main measures more effective. These include the following:

1. Traffic light measures coordinated to improve traffic flow and to enhance the travel time of public transit. An example is computer coordinated traffic signals in Greensboro, NC.

2. Variable message signs can be used to provide drivers with up to the minute information about traffic conditions. These have also been installed in key locations in the Piedmont Triad of North Carolina (e.g. Finch et al, 1994).

3. Ramp metering is used to space vehicles to smooth the flow of traffic and is used in large urban areas in the United States (e.g. Salem and Papageogiou, 1995).

Combinations of TDM measures will enhance their impacts. Packages of main and complementary strategies are particularly effective. For example, carpooling can be encouraged by a good computer match system along with HOV lanes on key highways and priority parking for reduced rates at places of employment. Bus priority traffic lights can be combined with HOV lanes, turn restrictions, dedicated bus lanes and vehicle information systems to make bus competitive in both cost and time and to promote the use of transit (e.g. Jones, 1991, SAVE, 1996 and ELGAR, 1996).

In their handbook on TDM, The U.S. Center for Transportation Research (1996), TDM is divided into eight groups which is summarized in Table 1.