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GLOSSARY
Accessibility Accessibility measures the relative ease with which
one can reach desired destinations. See mobility.
Activity space Geographic space within which a population tends to
circulate.
Affected population Population that would experience the beneficial and
adverse effects of a transportation system change.
Air quality index (AQI) An index for reporting daily air quality. It focuses on
health effects due to breathing polluted air and
includes five major pollutants: ground-level ozone,
particulate matter, carbon monoxide, sulfur dioxide,
and nitrogen dioxide.
American Association of State AASHTO is a nonprofit, nonpartisan association
Highway Transportation Officials representing highway and transportation departments
(AASHTO) in the 50 states, the District of Columbia, and Puerto
Rico.
American Society for Testing Founded in 1898, ASTM International is a not-for-
Methods (ASTM) International profit organization that provides a global forum for
development and publication of voluntary consensus
standards for materials, products, systems, and
services.
ALOHA model Areal Location of Hazardous Atmospheres (ALOHA)
model.
Artist's sketches A method of presenting alternative proposals for a
transportation facility whereby respondents can react
to renderings of aesthetic features.
Average annual daily traffic (AADT) The average number of vehicles passing a point on a
roadway per day based on an annual average of daily
traffic rates. Actual daily traffic rates may vary
somewhat from the AADT because of seasonal
variations, special events, and other phenomena.
Barrier effect The reduction in mobility and safety of nonmotorized
travel caused by the construction of new transportation
projects such as those that increase traffic volumes
and speeds on existing roads.
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Benefit-cost analysis An analysis that compares the potential benefits of a
project with the estimated costs of the project. If the
potential benefits outweigh the expected costs, the
analysis suggests that the project will benefit society
in general.
Bicycle Compatibility Index (BCI) A composite level-of-service measure for bicycle
condition evaluation. Standard BCI values represent
abilities and preferences of average adult cyclists.
Bicycle Safety Index (BSI) An index that enables one to estimate the safety of
bicyclists riding on a roadway that has certain
characteristics. These characteristics include traffic
levels, speed limit, and a series of physical attributes.
Categorical exclusion (CE) A component of the NEPA process. A CE can result
from a determination that a project would have no
significant environmental impacts and therefore that
an expedited permitting process can be followed. See
environmental assessment and environmental impact
assessment.
Census Transportation Planning A data package available from the U.S. Census
Package (CTPP) Bureau for most major metropolitan areas that
contains demographic data and self-reported journey-
to-work travel times. The data are available by
jurisdiction within the metro area.
Charrette A meeting to resolve a problem or issue. Within a
specified time limit, participants work together
intensely to reach a resolution. The sponsoring agency
usually sets the goals and time limit and announces
them in advance.
Chi-square test A statistical test that can be used to determine if a
particular type of impact would be experienced
differently by protected populations.
Community cohesion The amount and quality of social networking among
members of a community.
Comprehensive Environmental The federal law otherwise known as "Superfund"
Response, Compensation and under which hazardous waste remediation is
Liability Act (CERCLA) conducted.
Computer-aided design and drafting Computer graphics software that is commonly used to
(CADD) software make architectural and engineering drawings and for
making technical illustrations of any kind. It also
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enables you to revise drawings quickly and with
minimal effort.
Consolidated Federal Regulations A compilation of proposed, new, and amended federal
(CFR) regulations that have been published in the Federal
Register.
Cost-effectiveness analysis Several alternatives are compared to determine which
would achieve the desired outcome at the lowest cost.
Council on Environmental Quality Coordinates federal environmental efforts and works
(CEQ) closely with agencies in the development of
environmental policies and initiatives. The CEQ has
oversight of the federal compliance with Executive
Order 12898 and NEPA.
Descriptive statistics The branch of statistics concerned with (1)
summarizing the distribution of a single variable or (2)
measuring the relationship between two or more
variables.
Distributive effects Measurable adverse and beneficial outcomes of a
transportation plan, program, or project that do not
affect all people within an area equally.
Distributive effects analysis An analysis that compares potential effects, positive
and negative, of publicly funded projects or services
on various population groups and (in some instances)
on individuals or subgroups within groups.
Double-counting Counting a particular effect twice, either explicitly or
implicitly. For example, adding transportation cost
savings to the economic effects brought about by these
savings may result in an overestimation of the
economic effect of a project.
Economic development The process of expanding economic activity in an area
to provide more jobs and income to that area's
residents.
Emergency Response and The primary national database used to report and track
Notification System (ERNS) hazardous material spills.
Emissions factor (EMFAC) The relationship between the amount of pollution
produced and the amount of raw material processed.
Environmental assessment (EA) A component of the process mandated by the National
Environmental Policy Act of 1970, as amended. An
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EA is a concise public document that includes a brief
discussion of the rationale behind the proposed
project, alternatives to the proposed action, the
probable environmental impacts of the proposed
action and its alternatives, and a listing of agencies
and persons consulted. The EA must show why the
impacts are not significant or how they can be
mitigated to become nonsignificant.
Environmental impact statement Also a component of the NEPA process. An EIS is an
(EIS) analytic document that informs decision-makers and
the public of the potential environmental effects of the
proposed project, as well as those of any reasonable
alternatives. It must be completed when impacts
would likely be significant, and it must show how they
would be mitigated.
Environmental justice Environmental justice is concerned with a variety of
public policy efforts to ensure that adverse human
health or environmental effects of governmental
activities do not fall disproportionately upon minority
populations and low-income populations.
Environmental Justice Index (EJI) An index describing level of environmental justice
concerns based on minority population, low-income
population, and population density factors.
Executive Order (EO) 12898 An executive order on environmental justice signed by
President Clinton on February 11, 1994. The order
obligates each federal agency to identify and address
disparate effects of policies, programs, and activities
on low-income populations and minority populations.
Equity An often-elusive concept that pertains to fairness of
distribution of the benefits and costs of a
transportation project among population groups. There
are several measures of equity but, in the end, what is
equitable depends on personal, individual definitions
of fairness.
Federal Highway Administration The administrative unit within the U.S. Department of
(FHWA) Transportation charged with improving and
maintaining designated roadways across the nation. It
also is responsible for carrying out various federal
policies that apply to surface transportation.
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Federal Insecticide, Fungicide and The primary focus of FIFRA is to provide federal
Rodenticide Act (FIFRA) control of pesticide sale, distribution, and use.
Federal Transit Administration (FTA) The FTA assists in developing improved mass
transportation system for cities and communities
nationwide. Through its grant programs, FTA helps
plan, build, and operate transit systems with
convenience, cost, and accessibility in mind.
Finite element flow (FEFLOW) A model that provides an advanced two-dimensional
and three-dimensional environment for performing
complex groundwater flow, contaminant transport,
and heat transport modeling.
Fixed-guideway transit Any public transit service that uses exclusive or
controlled rights-of-way or rails. This includes heavy
rail, commuter rail, light rail, trolleybus, aerial
tramway, inclined-plane cable car, automated
guideway transit, ferryboats, and the portion of motor
bus service that operates on exclusive or controlled
rights-of-way and high-occupancy or toll (HOT) lanes.
Focus group A small group discussion with professional leadership.
A carefully selected group of individuals convenes to
discuss and give opinions on a single topic.
Participants are selected in two ways: (1)random
selection is used to ensure representation of all
segments of society or (2) nonrandom selection can
help clarify a particular position or point of view.
Geographical information system A computer system capable of assembling, storing,
(GIS) manipulating, and displaying geographically
referenced information. GIS enables spatial data files
to be layered for purposes of analysis or presentation.
Global positioning system (GPS) A worldwide radio-navigation system involving a
constellation of 24 satellites and their ground stations.
GPS receivers use signals from these satellites to
accurately compute positions relative to the face of the
earth.
GMS 4.0 (Groundwater Modeling A comprehensive program with tools for every phase
System) of a groundwater simulation, including site
characterization, model development, postprocessing,
calibration, and visualization.
Gravity model A method of analysis that generally assumes the
number of trip ends at a destination location to be
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proportional to the size or attractiveness of the
destination and inversely proportional to a measure of
separation between this location and various origin
zones. Gravity models are routinely used in travel
demand models to forecast how many trips will be
made to each destination from a given origin.
Ground-level air quality (microscale, Air quality in the lower atmosphere very near the
or hot spot) source of emissions, such as around an intersection.
Corps of Engineers Hydraulic A water surface profile model for steady and unsteady
Engineering Center River Analysis one-dimensional, gradually varied flow in both natural
System (HEC-RAS) and constructed river channels.
HEC-2 A water surface profile model for steady, gradually
varied flow in natural and constructed channels.
Highway Economic Requirements A computer model developed for FHWA to assist
Model (HERS) and HERS-ST state and local governments in programming their
highway resources. HERS contains routines to
estimate the economic benefits of potential
transportation projects.
Highway Performance Monitoring A national highway information system that includes
System (HPMS) data on the extent, condition, performance, use, and
operating characteristics of highways.
Horizontal equity Horizontal equity refers to the equitable distribution of
benefits and costs within a group.
Incident An event that reduces the performance level of a
roadway, including crashes, vehicle breakdowns, and
debris on the road. Incidents are random events, but
the likelihood of their occurrence is affected by the
design and condition of the roadway, as well as by the
congestion level on the roadway.
Initial Isolation Zone (IIZ) The radius of a zone around an accidental release of
toxic chemicals from which all people not directly
involved in emergency response are to be kept away.
ISTEA Intermodal Surface Transportation Efficiency Act of
1991.
Leaking underground storage tank Underground storage tanks (e.g., gasoline) that have
(LUST) uncontained leaks.
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Level of service (LOS) A concept that describes traffic conditions and
associated traffic flow rates. Six levels of service are
typically recognized: A (free flow) through F (stop-
and-go waves). The concept of LOS also is applied to
gauge the performance of nonmotorized transportation
(e.g., the ability of pedestrians to cross a major urban
street).
Likert scale A composite measure that attempts to improve levels
of measurement through the use of standardized
response categories in survey questionnaires.
Response categories may include strongly agree,
agree, neither agree nor disagree, disagree, and
strongly disagree.
Major investment studies (MIS) Federally mandated studies in which MPOs examine
which alternative transportation strategy, or mix of
strategies, would best solve transportation problems
within particular corridors.
Metropolitan Planning Organization A transportation policy-making organization made up
(MPO) of representatives from local government and
transportation authorities. They are required for any
urbanized area with a population greater than 50,000.
Federal funding frequently is channeled through
MPOs.
Mobile Emission Assessment System Model-based method used for developing pollution
for Urban and Regional Evaluation surfaces.
(MEASURE)
Mobility The ability of people to move about and make use of
various transportation modes. See accessibility.
Mode The method of transportation by which people travel
or goods are shipped.
Motor Carrier Management The Federal Motor Carrier Safety Administration
Information System (MCMIS) (FMCSA) operates and maintains the MCMIS.
MCMIS contains information on the safety fitness of
commercial motor carriers and hazardous material
(HM) shippers subject to the Federal Motor Carrier
Safety Regulations (FMCSRs) and the Hazardous
Materials Regulations (HMRs).
National Ambient Air Quality Directed by the 1990 Clean Air Act and created by the
Standards (NAAQS) U.S. EPA, these standards are designed to protect
human health and the public welfare. Primary
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standards protect human health; secondary standards
protect public welfare.
National Environmental Policy Act of A federal law enacted January 1, 1970, to ensure that
1969 (NEPA) federal agency decision-making takes environmental
factors into consideration. State and local entities must
comply with NEPA when they are involved in federal
actions (e.g., using federal funding for a project).
National Personal Transportation A survey conducted periodically by FHWA to
Survey (NPTS) measure travel of American households, focusing
primarily on local, repetitive travel. NPTS data are
intended to provide insights on travel by trip purpose
and mode, social and economic characteristics of the
trip makers, changes in vehicle ownership, vehicle and
fuel usage, the changing travel patterns of women and
minorities, and changes in the mobility of the older
driver population.
National wetlands inventory (NWI) An inventory of wetlands maintained by the U.S. Fish
and Wildlife Service. Databases are available in
digital (computer readable) format and are compatible
with GIS software.
Network An integrated series of road segments that behave as a
system. Thus, a change in one road segment often will
affect the performance of others.
Noise abatement criteria (NAC) Noise levels established by FHWA for a series of
activity categories (i.e., land uses). If a proposed
project would result in noise levels higher than the
NAC, noise abatement measures must be taken.
Origin-destination (O-D) pair The passage of traffic originating at one node on the
network and traveling to another along a unique path.
Office of Solid Waste and The office within U.S. EPA that oversees
Emergency Response (OSWER) implementation of most hazardous waste regulations.
In response to Executive Order 12898, OSWER has
had a policy on environmental justice since 1994.
Protective action distance (PAD) The downwind distance from a release that defines a
zone in which persons should be either evacuated or
sheltered-in-place.
Paratransit The use of small buses or vans to provide transit
services for transportation-disadvantaged groups, such
as people with significant physical disabilities, and
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nondrivers who require medical or social services.
Paratransit may also include flexible route, door-to-
door transit service to the general public.
Pass-by traffic Traffic that both originates in, and is destined for,
locations outside of the local area in which it is
traveling.
Pedestrian danger index The number of pedestrian injuries and fatalities in an
area of analysis divided by the area's population. This
number is then divided by a number representing the
overall level of pedestrian activity in the area.
Phase 1 environmental site Initial evaluation of a transportation corridor for the
assessment (ESA) existence of contaminated sites. The ESA may be
undertaken as a portion of the NEPA environmental
review, in preparation for property acquisition, or
before construction in a right-of-way zone.
Photomontage A photo-realism technique in which images of various
alternatives are superimposed on an image of the
existing environment. It allows respondents to
evaluate the positive or negative effects of each
project alternative in relation to the existing
environment.
Price elasticity of demand A measure of consumer response to a change in price
calculated by dividing the percentage change in
quantity by the percentage change in price.
Privacy An issue in sociodemographic data, privacy generally
is understood to mean that the information conveyed
is not specific (i.e., disaggregate) enough for the
attributes of a single household, person, or business to
be revealed. To ensure the privacy of individuals, the
US. Census Bureau may suppress data when only very
small numbers of observations are present.
Progressive A project or financing approach in which the cost
burden is disproportionately higher for persons with
larger incomes or the benefits accrue primarily to
persons with lower incomes. See regressive.
Property damage only (PDO) crashes Motor vehicle crashes in which there are no fatalities
or personal injuries but property is damaged. This
property may be the involved vehicle(s) or other
property that is struck by a vehicle.
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property that is struck by a vehicle.
Protected population Groups of people defined by age, disability, gender,
religion, class, race, low-income, limited English
proficiency, and national origin.
Qualitative analysis An approach that involves considering qualities or
attributes that do not lend themselves to
quantification. It can be applied to assess people's
general feelings toward alternatives by evaluating the
way they respond to a series of nonmetric indicators,
such as aesthetic quality.
Quality of life A general way of expressing the presumed ultimate
objective of any form of public action. There are
numerous dimensions to quality of life, which are
valued differently by different people. Among the
normally included dimensions are safety, access to
opportunity, clean air and water, and social tolerance.
Raster A method of coding and storing a graphic image as a
pattern of dots. Also known as a bitmap.
Regional air quality Air quality in a region or large area.
Regression analysis A statistical technique used to assess the extent to
which one or more measures are related to a criterion
measure. For example, household rent may be affected
by a series of attributes of a property. How much each
of these attributes affects rent, given the presence of
the other attributes, can be assessed using regression
analysis.
Regressive A project or financing method that results in persons
with lower incomes paying a larger share of their
income for a project or a project whose benefits
largely accrue to those with higher incomes. See
progressive.
Rent theory A concept that explains how increased access to a
location tends to encourage more intensive use of land
at that location.
Resource Conservation and Recovery The primary goals of the Resource Conservation and
Act (RCRA) Recovery Act (RCRA) are to protect human health
and the environment from the potential hazards of
waste disposal, to conserve energy and natural
resources, to reduce the amount of waste generated,
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and to ensure that wastes are managed in an
environmentally sound manner.
Road segment A short portion of a roadway, often a half-mile or so
in length, that is the unit of analysis in safety
evaluations and in road network models.
Roadway geometry Specific design elements of roadways, including
number of lanes, lane width, median type and width,
length of acceleration and deceleration lanes for on-
and off-ramps, curve radii, and roadway alignment.
SARA Superfund Amendments and Reauthorization Act of
1986.
SAVIAH Small Area Variations in Air Quality and Health.
Scale economies Reductions in average costs that come about through
increases in the output (i.e., scale) of plants and
equipment.
Sensitive noise receptor A person or activity that is particularly vulnerable to
traffic noise (e.g., hospitals, rest homes, schools, or
houses of worship).
Sensitivity analysis The process of analyzing how changes in one factor
(e.g., population growth assumptions) influence a key
outcome such as traffic volume. Often the factor to be
varied is the basis for several scenarios. For example,
one might construct several scenarios based on
different population growth projections.
State Implementation Plan (SIP) EPA-approved state plans for the establishment,
regulation, and enforcement of air pollution standards.
State Transportation Investment A fiscally constrained and prioritized program of
Program (STIP) projects to which state and local transportation
agencies have committed over a three-year period. A
STIP is required to receive federal funding. Projects
within metropolitan areas are contained in the relevant
TIP and are referenced in the STIP.
Stated preference surveys A citizen survey in which respondents are asked to
state their preference for one of two attributes at a
time. A series of such pair-wise comparisons are made
to estimate how people's preferences are ordered.
Storm Water Management Module EPA's storm water and wastewater management
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(SWMM) modeling package for analyzing urban drainage
systems and sanitary sewers. The MIKE-SWMM
application provides users with a complete, graphical,
easy-to-use interface.
TEA-21 Transportation Equity Act for the 21st century, enacted
in 1998.
Topographically integrated Digital files that contain line and polygon information
geographic encoding and referencing representing boundaries of census tracts, block groups,
(TIGER) files and blocks, as well as the locations of streets and
roads.
Toxic by inhalation (TIH) Classes of chemicals that are toxic by inhalation or
that produce TIH gases when they react with water
(referred to as TIHWA).
Toxic Substances Control Act The Toxic Substances Control Act (TSCA) of 1976
(TSCA) was enacted by Congress to give EPA the ability to
track the 75,000 industrial chemicals currently
produced in, or imported into, the United States.
Toxics Release Inventory (TRI) Database of toxic releases in the U.S. compiled from
the Superfund Amendments and Reauthorization Act
of 1986 (SARA) Title III Section 313 reports.
Traffic analysis zone (TAZ) Small geographic areas that represent urban areas in
travel simulation models. TAZs are characterized by
population, employment, and other factors and are the
places where trips begin (i.e., trip producers) or end
(i.e., trip attractors).
Traffic calming A combination of mainly physical measures that
reduce the negative effects of motor vehicle use, alter
driver behavior, and improve conditions for
nonmotorized street users. Expected consequences
include safer roadways for pedestrians, bicyclists, and
neighborhoods in general. Specific road design
characteristics include speed bumps and traffic circles.
Traffic demand models Models used to calculate changes in travel time
between specified origins and destinations that might
be the result of transportation projects, such as
changes in road capacity. A limitation of these models
is that they rarely take into account non-motorized
transportation modes. Same as travel demand models.
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Traffic noise Any unwanted noise generated from four major
sources: tire/pavement interaction, engine noise,
exhaust noise, and brakes.
Traffic Noise Model (TNM) Noise-prediction software. Developed by FHWA,
TNM is the successor to STAMINA and offers clear
improvements over it, including modeling for free-
flow and stop-and-go traffic conditions.
TRANPLAN A set of integrated computer programs that encompass
a four-step travel demand model. It operates within a
GIS environment.
Transportation Analysis and An integrated system of travel forecasting models that
Simulation System (TRANSIMS) includes a population synthesizer, activity generator,
route planner, and traffic microsimulator.
TransCAD A GIS-based computer model that stores, displays,
manages, and analyzes transportation data. It has
modules for routing and travel demand forecasting.
Transportation choice The quantity and quality of transportation options
available in a geographic area. Choice is an especially
complex issue for those who are economically or
physically challenged.
Transportation conformity Process of coordinating the transportation planning
and air quality planning processes. This conformity is
achieved when the TIPs are consistent with SIPs.
Transportation demand management Programs designed to maximize the people-moving
(TDM) capability of the transportation system by increasing
the number of persons in a vehicle or by influencing
the time of (or need to) travel. TDM programs must
rely on incentives or disincentives to make those shifts
in behavior attractive.
Transportation disadvantaged People who face significant unmet transportation
needs.
Transportation Improvement Plan A federally mandated regional transportation
(TIP) improvement plan developed by a metropolitan
planning organization (MPO). The TIP outlines the
staged development of the area's fiscally constrained
long-range transportation plan with priority projects
identified.
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Travel demand (TD) models A series of mathematical equations used to represent
how choices are made when people travel. Such
models require a series of assumptions, and the
parameters in the equations are calibrated to match
existing data. The models are used to forecast future
travel. Generally, these models have four steps: trip
generation, trip distribution, mode split, and traffic
assignment.
Travel Model Improvement Program A continuing research program to help planning
(TMIP) agencies improve their travel analysis techniques. A
major product of this program has been the
TRansportation ANalysis SIMulation System
(TRANSIMS), a new form of travel modeling
technology.
Travel time variability Uncertainty as to the amount of time a trip will take or
the time at which one will arrive. For just-in-time
industries or commuters, travel time variability often
is as important as average travel time.
Triangular irregular network (TIN) A surface representation derived from irregularly
spaced sample points and break-line features. Each
sample point has an x,y coordinate and a surface, or z-
value. These points are connected by edges to form a
set of nonoverlapping triangles used to represent the
surface.
Trip purpose The reason why a trip is made. The purpose of a trip
influences the mode used, the time at which the trip is
made, the length of the trip, and other trip attributes.
Common trip purposes include work and work-related
business, shopping, and social/recreational interaction.
Underground storage tank (UST) A storage tank designed to contain chemical
compounds such as hydrocarbons that is located below
ground level. USTs and above-ground storage tanks
(ASTs) can be sources of toxic releases.
Universal access Transportation facility design that accommodates
people with a range of needs, including wheelchair
users, people who walk with difficulty or are
vulnerable to falls, people who have visual disabilities,
and pedestrians who are pushing strollers or handcarts.
Urban form The array of land uses and their densities within an
urban area. Urban form is influenced by transportation
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facilities that affect the relative accessibility of
different locations.
Urban Transportation Planning A system of analytic tools and methods developed by
System (UTPS) the U.S. Department of Transportation in the 1970s to
facilitate the four-step travel demand modeling
process. See travel demand models.
U.S. Environmental Protection EPA's mission is to protect human health and to
Agency (U.S. EPA) safeguard the natural environment--air, water, and
land.
Vehicle hours traveled (VHT) The number of hours spent on a specific road segment
or within a road network by the vehicles operating on
it per unit of time, generally a day. For a given volume
of traffic, higher flow speed (e.g., less congestion) will
lead to a reduction in VHT.
Vehicle miles traveled (VMT) The number of miles driven by the vehicles using a
specific road segment per unit of time, usually a day.
VMT is equal to the traffic volume multiplied by the
length of the roadway. See AADT.
Vehicle operating cost (VOC) The variable cost to vehicle owners of operating these
vehicles on roadways per mile of travel. Included in
VOC are fuel and oil consumption, wear and tear,
depreciation, and insurance. Flow speed, as well as
road geometry and other physical attributes, can
influence VOC.
Vertical equity Equitable distribution of benefits and costs among
groups. Groups are usually distinguished by wealth or
income.
Viewshed An area that can be viewed from a particular site or
roadway. Communities may adopt ordinances to
reduce the impact of man-made structures and grading
on views of existing landscapes and open spaces as
seen from public roads.
Virtual metropolitan model A model that combines several visual computer
models to create a comprehensive virtual model of an
entire metropolitan area. Virtual metropolitan models
are constructed by combining aerial photographs with
street-level imagery and 3-D geometry to produce
realistic simulations of large urban environments.
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Visual acuity The ability of the eyes to resolve detail.
Visual preference survey (VPS) A form of resident survey that allows respondents to
express their preferences for certain types of
development rather than for specific proposals.
Through a series of slides, respondents rate their
attitudes regarding images, which are later analyzed to
produce a consensus of resident preferences.
Volume-to-capacity (V/C) ratio The ratio of the number of vehicles traveling on a
roadway to the number that would result in a slowing
of traffic to a specified speed. This level of traffic is
defined as the effective capacity of the roadway. In
general, congestion begins to set in at a V/C ratio of
about 0.8.
Weighted decibels (dBA) Units of sound that include an adjustment whereby
high- and low-pitched sounds are given higher scores.
The objective is to approximate the way humans hear
sounds.
Windshield survey An inventory of land uses and an observation of
natural and human environments collected visually,
generally by driving through a corridor in which
changes are proposed.
Wire-frame model A type of visual computer modeling commonly used
for proposed transportation projects. Wire-frame
models are derived from a continuous series of
roadway cross sections that are linked together to form
a 3-D model of the proposed roadway design.
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