Cover Image

Not for Sale



View/Hide Left Panel
Click for next page ( 163


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 162
CHAPTER 7. TRANSPORTATION USER EFFECTS OVERVIEW Transportation system changes generally benefit users by reducing travel time, improving safety, and lowering vehicle-operating costs. A transportation system change may also improve the choices available to travelers by offering them different routes or modes of travel at different times of the day. A change can also increase the number of accessible destinations. In terms of environmental justice, the point of interest is the extent to which minority populations or low- income populations would experience these benefits. To understand the distributive effects that would result from a potential transportation project, it is first necessary to examine the performance of the existing transportation service, including how this service varies between members of protected populations and others. Then, a reasonable comparison can be made between the existing service and the new service that would result from a system change. In general, system performance may be measured by the volume-to- capacity (V/C) ratio and by the accessibility of destinations that the affected populations consider important. Thus, the methods presented in this chapter focus on changes in accessibility and changes in transportation choice. Geographic information systems (GIS) are capable of combining and analyzing layers of data about a location and thus are well suited for analyzing distributive effects. A detailed account of applying GIS mapping as part of an assessment is provided in Appendix C. GIS will also be the major method used to assess changes in transportation choice. Accessibility Accessibility is the ability to reach desired destinations. It is related to, but different from, mobility, which is the ability to move. If a population group has limited mobility (e.g., people with low incomes may be less likely to own automobiles), achieving accessibility will require a residential location that is near places where essential activities are conducted, such as work, school, shopping, worship, child care, social services, and recreation. In general, accessibility has two main components: (1) the physical ability to reach a desired destination and (2) the degree of difficulty in reaching it. If a destination can be reached, travel time is the measure most often used to assess the difficulty or ease of reaching it. Travel time is greatly affected by the level of congestion on road segments; by how directly the road system connects trip origins and destinations; and by the standard and condition of applicable road segments. In our analysis of accessibility, we treat vehicle operating costs as a function of travel time, even though a more engineering-oriented approach would take into account pavement surface quality and related variables when evaluating road segment performance. Our primary focus is on travel demand analysis that is specific enough to assess differential effects on protected populations versus travelers in general. We are aware, however, that the process of developing more refined and accurate measures of system performance continues. More comprehensive evaluation 167

OCR for page 162
models are currently being developed, and some will be operational soon. Thus, we also provide a brief overview of future generation, activity-based techniques for assessing road system performance and accessibility. Transportation choice Closely related to accessibility is transportation choice, which refers to the quantity and quality of transportation options available to residents of an area. Most communities have transportation systems that are strongly auto oriented. Very few options are available for those who either prefer an alternative mode or are not able to travel by auto. Because public transportation planning is beyond the scope of this guidebook, we focus on pedestrian travel as well as non- motorized transportation, particularly bicycling. It is not unusual for a road project to affect, either positively or negatively, the ability of people to use other transportation modes. More specifically, there are at least four reasons why individuals and communities may value having choices among transportation modes: To help achieve equity goals. A lack of transportation choice limits the personal and economic opportunities available to people who are physically, economically, or socially disadvantaged. Often, such individuals have less access (or less reliable access) to an auto, and so may face barriers to mobility in auto-dependent communities. To serve as a back-up option for those who can drive. People who do not habitually use an alternative mode may value its availability at some point in the future or in the case of an emergency. Many people can expect to go through periods when they must rely on alternative modes of transportation due to age, physical disability, financial constraints, vehicle failures, or major disasters that limit automobile use. To increase transportation system efficiency. Use of alternative modes can help achieve certain transportation demand management (TDM) objectives, including reduced traffic congestion, facility cost savings, and environmental quality. To increase livability. Many people enjoy using alternative modes, such as walking and bicycling or riding the bus, and they value living in or visiting a community where these activities are safe, pleasant, and readily available. Some alternative modes are more prevalent than others, and not every analysis need consider every alternative mode. Public participation and dialogue with local officials can help in the selection of modes that need to be examined. A key element in environmental justice is to ensure that protected populations have mobility that is comparable to that of other populations; this often means that transportation modes other than the auto must be available. New or upgraded transportation facilities may affect the viability of alternate transportation modes in three major ways: Upgrading roads can increase vehicular traffic. Heavily traveled roads are more likely to be dangerous, difficult to traverse, and unpleasant for those traveling via something other than a motor vehicle. As traffic increases, so does the risk to bicyclists and 168