Up until the early 1990s, transportation planners used only macro-scale analysis for modeling travel behavior on major roads and transit systems. Macro-scale transportation features in the real world are major roadways, commuter rail, transit lines, and development at a scale that ignores non-motorized travel. Macro-scale travel forecasting, the prevailing model, relies on large transportation analysis zones using averaged demographic data.
"Micro-scale design" (MSD) is a term that has been coined recently by transportation and land use planners to describe the human-scale features of the built environment. This concept focuses on accessibility to desired activities rather than on mobility; the latter requires more transportation facility capacity. MSD describes the physical features of development at the level-of-detail of a neighborhood or a single building site.
MSD features are concerned with bicycle, pedestrian and transit access-oriented facilities such as:
The physical features of the neo-traditional neighborhood development (NTND), transit-oriented development (TOD), and the new urbanism contain elements that we would classify as MSD. For example, all three of these settlement patterns incorporate residential, commercial, and community land uses within walking distance of each other. In most cases, accessibility to a regional transit system is an important element or even the focal point of the design of the development. These same features may be found in new communities that are designed to be 'sustainable' in the future, i.e., not dependent upon travel by fossil fuel-powered vehicles.
Frustration with suburban sprawl has led to a resurgence of pedestrian- and transit-oriented development and has raised questions about the impact of these new development patterns on travel behavior. Along with this has come the realization that the existing regional travel models were insensitive to the relationship between these newer developments and travel behavior. For example, transit ridership varies greatly as a function of the difficulty of crossing streets at bus stops and the presence of waiting shelters and sidewalks, but these micro-scale design features are not recognized in most regional models.
"The longest journey begins with a single step" - this proverb succinctly describes the relationship between micro-scale design elements and regional travel. Settlement patterns and site design considerations play a central role in personal travel choice, frequently by acting as a constraint on the choices that might be available.
In response to questions about the true ability of NTNDs and TODs to reduce the need for automobile travel, planners and researchers have been exploring the influence of neighborhood development on vehicle use and have been searching for methods to model this micro-scale behavior in a satisfactory manner. The U. S. Environmental Protection Agency (EPA) and the U. S. DOT Federal Highway Administration (FHWA) are interested in how effectively these settlement patterns reduce mobile emissions and contribute to improving air quality. Many of these activities are in response to conformity with the requirements of the Clean Air Act Amendments of 1990, the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA), and the Transportation Equity Act for the 21st Century (TEA21).
Accomplishing the transportation system model-builder's goal of an ideal travel model requires the collection and interpretation of more data than has been used in travel forecasting activities. The ideal level of detail is much finer than typically encountered in travel forecasting models in use today. In this context, MSD elements address the human-scale features of the transportation system and settlement patterns - sometimes classified as urban design or urban form - and focus on those site characteristics that enter into an individual's decisions about activity selection and consequential travel choices.
The anticipated audience for this report is the group of transportation and land use planners who will be collecting travel behavior data or modifying their existing transportation models to incorporate MSD elements.
There are several hurdles to effective modeling of the influence of MSD features on travel behavior using regional models:
MSD is highly visual and amenable to graphic presentation, and thus has been approached from the fields of architecture and landscape architecture as well as engineering and urban planning. There are numerous publications that present excellent graphics displaying settlement patterns that have worked and schemes that are predicted to provide a quality of life and an environment that fosters independence from the single-occupant automobile. More than 25% of the residents of the United States do not drive 1, and many more would prefer to not have to drive, particularly on high-volume roads. Therefore, it seems only natural to explore development methods that produce successful combinations of the MSD features.
This report is not intended to present design guidelines for the implementation of TOD or NTND. Instead, it presents illustrations of the salient features of development that fosters non-motorized travel, and provides references for those who are planning the human settlements of the future. There have been attempts to rank streetscapes and urban design characteristics in terms of their transportation impacts, with some results presented in Appendix C.
The purpose of this report is to:
The study team assembled an expert panel for this report, representing both academic and practical perspectives. Panel members were: Elizabeth Deakin, University of California, Berkeley; Ronald Eash, Chicago Area Transit Study; Robert Dunphy, Urban Land Institute; and Robert Griffiths, Metropolitan Washington, DC Council of Government. The panel reviewed the progress of the project, modeling issues, and the research on MSD issues included in the appendix and offered feedback to the study team.
Chapter 1 provides a brief description of MSD and the reasons for preparing this report.
Chapter 2 describes MSD parameters that have been investigated, tested, and reported in the literature. In this chapter the MSD elements are discussed in terms of both their quantitative and qualitative attributes. Also discussed are the issues surrounding each of the parameters and, where available, their impact on travel behavior.
Chapter 3 presents approaches being developed and used by metropolitan planning organizations (MPOs) to incorporate the MSD parameters in the travel demand models, recognizing that a number of MPO models in use today are at different levels of detail and precision. Descriptions of each of eight steps in the current travel forecasting process are given, from network development through trip assignment. The described work is either in progress or is being completed by MPOs and universities to extend the suite of travel demand models, so that the models become more sensitive to MSD features and their impact on travel decisions.
Appendices contain excerpts or summaries of various programs to support the material presented in Chapter 3. These appendices are designed for the practitioner who is interested in more detail on the measurement of MSD parameter values and modeling their impact on transportation.
Appendix A contains tables of MSD variables that have been postulated and/ or tested in academic or MPO projects. The Appendix tables include descriptions of the variables, their source, and some characteristics of their makeup.
Appendix B contains a table summarizing a survey of MPO activities particularly in terms of their surveys used to calibrate and validate their model systems. It also summarizes the status of their modeling process with respect to non-motorized travel.
Appendix C, summarizes the methods and conclusions of an "Accessibility Measure and Transportation Impact Factor Study" prepared by J H K and Associates for the Oregon Department of Transportation and the Oregon Department of Land Conservation and Development. This excerpt describes major steps, grading and scoring systems, and the transportation impact factors from this major study. For purposes of this study, "accessibility" is a composite variable containing measures of proximity, pedestrian access environment and the attractiveness of the destination.
Appendix D summarizes a paper by Ryan and Han on Vehicle Ownership Models Using Family Structure and Accessibility. The important contributions of this work are the use of density as an indicator of auto parking costs and space availability, and the use of accessibility measures to estimate the relative importance of owning a motorized vehicle.
Appendix F summarizes transit-friendliness factors as used in the Research Triangle Study and similar to the pedestrian environmental factors implemented in Portland, Oregon by 1000 Friends and the Transit Serviceability Indices developed by the Maryland National Capital Park and Planning Commission in Montgomery County, Maryland. This study examines the ability of micro-scale factors to explain the variation in transit use among different zones in the region.
Appendix G presents a compilation of pedestrian and bicycle levels of service from various sources that represent the beginnings of bicycle compatibility variables and models that estimate non-motorized travel using the regional modeling process as a basis.
Appendix H summarizes a network development guideline prepared for Oahu, Hawaii. In this highway network, the links have been coded with characteristics that can be used in the future to estimate pedestrian and bicycle travel. Also in this modeling effort, transit networks and zones were structured and estimated in ways in which they could be used to evaluate pedestrian and bicycle friendliness.
Appendix J contains a review of modeling practice and the planning environment leading up to the present requirements to include land use and MSD variables in the model.