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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
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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
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