Background. Research and applied practice have attempted to define the nature of land use and travel behavior for several decades. Seminal figures in planning, architecture, human health, engineering, and environmental fields have each placed their imprint on the understanding of how human living environments shape the actions of people within those environments, as well as measuring the consequences of human-environment interactions on both parties.
Since the 1970 and 1990 amendments to the federal Clean Air Act of 1963, an increasing number of studies have suggested that land use can also indirectly influence emissions of airborne pollutants. These pollutants are largely produced through the use of internal combustion engines operated in private automobiles and trucks, among other point and area sources. The theories have a similar origin, suggesting that land use patterns influence trip making frequency, trip lengths, choice of what mode of transportation to take, and so forth. A wide variety of approaches and technical strengths are exhibited in this body of literature, but the overwhelming majority of conclusions cite that land use patterns do (1) influence the trip making behavior of individuals; and (2) when measured, these travel changes in turn influence emissions from private automobiles and trucks when measured over a broad area.
To understand the past research and current practice, the Federal Highway Administration sponsored a research project that would address the following objectives:
Critically review existing literature and research on the topic of land use, travel behavior, and emission interactions;
Conduct a series of interviews and case studies with acknowledged experts and practitioners that are currently conducting or supporting work in the area of quantifying the effects of land use on emissions; and
The report findings were oriented towards practitioners that are or might be conducting land use-emissions studies.
Key Findings. Fifty literature items were critically reviewed as part of this project, although more items were rejected after an initial review indicated that they did not discuss quantifiable results. The literature generally recognized the importance of density, diversity, and design elements (the "three D's" according to several authors) on trip-making behavior and therefore emissions. Researchers were able to develop elasticities to describe these effects, which ranged from near-zero to 0.35. Typical values ranged from 0.03 to 0.10. Although all of these figures imply that the relationship between land use characteristics and travel are relatively inelastic, they still indicate a responsiveness to change.
Many researchers acknowledged problems with data collection/availability, cross-correlation of key variables, objectivity in measurement, and boundary effects.
In addition to the critical review of the literature, the Research Team interviewed a number of researchers, private agencies, USEPA staff, and metropolitan planning organizations. The Research Team used the results of these interviews and case studies to establish the state-of-the-practice methodology for conducting quantifiable analyses of land use changes and their impacts to mobile source emissions. This process generally follows a four- or five-step process, the number of steps depending on the need/desire to disaggregate emissions into small subareas:
Develop inventories of land use and transportation infrastructure according to modeling needs;
Create a baseline (or "trend") scenario describing how future land uses might look if existing policies remain unchanged, and develop one or more alternative scenarios;
Input land use and transportation information for all alternatives into a travel demand model or other gravity-based tool;
Extract vehicle miles of travel by transportation facility, vehicular speeds, and other information required to estimate emission factors into an emission factor model (e.g., MOBILE or EMFAC); and
If the objective of the study includes examining emissions benefits conferred to subareas, disaggregate emissions into individual grid cells or other small units of geography. This can be done by some travel demand models (e.g., TransCADTM by Caliper Corporation) and emissions packages such as MODELS3 and CALINE.
More advanced applications make use of sophisticated land use models, integrated land use-transportation models, modified travel demand modeling techniques, or dispersion modeling to refine impacts on small areas and populations. Only two of the 11 case studies applied the results of their testing to attempt to receive an emissions reduction credit in a conformity or state implementation plan (SIP). In the Atlantic Steel case, while the project was shown as a transportation control measure (TCM) in the Georgia SIP, the State of Georgia elected not to take emissions credits for the project. All cases were either "visionary" exercises to study quality of life issues undertaken by MPOs and local governments, or were generated by a proposed large development that might affect the air quality standing in a transportation conformity maintenance area.
Recommended Improvements. The Research Team proposed a number of improvements to state-of-the-practice methods as well as ways to increase the dissemination of information and promote good practice in this area. Providing consistent document guidelines; establishing a central clearinghouse for case studies and guidance; and specific modeling improvements are recommended.
Appendices provide information about data resources, specific elasticity values, brief summaries of all case studies, and the critical review of literature stored in a MS-Access database on CD-ROM. This CD-ROM also includes the final report and papers/reports that were available to the Research Team during the course of this study.
The following people are considered contacts for more information about this report, its purpose, and its contents.
Cecilia Ho, Team Leader, Transportation Conformity
Federal Highway Administration
HEPN-10, Room 3240
400 7th Street, SW
Washington, DC 20590
Kenneth Hess, AICP, General Manager
The Louis Berger Group, Inc.
100 Halsted Street
East Orange, New Jersey 07018
(973) 678-1960x553 firstname.lastname@example.org
J. Scott Lane, AICP, Transportation Planning Manager
The Louis Berger Group, Inc.
1513 Walnut Street, Suite 250
Cary, North Carolina 27511
(919) 467-3885x14 email@example.com
The Research Team wishes to acknowledge the support of the Federal Highway Administration, Environmental Protection Agency Regional Office personnel, and the staffs of the metropolitan planning organizations.