Access, Accessibility
The opportunity to reach a given end use within a certain time frame, or without being impeded by physical, social or economic barriers. Typically, accessibility is the extent to which transportation improvements make connections between geographic areas or portions of the region that were not previously well connected.

Alternative
Generally, one of a set of transportation proposals under comparative study.

Arterial
A major street, primarily for through traffic, usually with unlimited access to adjacent streets.

Average Daily Traffic (ADT)
The average number of vehicles passing a fixed point in a 24-hour time frame. A way to measure traffic volume.

Base Year
The lead off year of data used in a study, usually the current year or a year with the most recent comprehensive data.

Build/No Build
As defined by the federal transportation legislation, Metropolitan Planning Organizations (MPOs) must demonstrate that “building” or implementing a long range plan (LRP) and Transportation Improvement Program (TlP) will provide more emissions reduction (improve air quality) than by “not building” or not implementing that same long range plan and TIP.

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Capacity
Usually the maximum number of vehicles and/or people that can be carried past a point on a transportation system in a specified time, at a specified level of service (LOS).

Collector
A road that collects and distributes traffic. Sometimes built next to an expressway to collect traffic from the area and then funnel it onto the expressway. Generally fewer lanes than an arterial.

Conformity
The process to assess the compliance of any transportation plan, program, or project with air quality control plans. The conformity process is defined by the Clean Air Act and related amendments.

Congestion Management System (CMS)
A plan developed by a Transportation Management Area (TMA) that provides for effective management of new and existing transportation facilities through the use of travel demand reduction and operational management strategies.

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Design Concept
In a major investment study, the type of facility (i.e. freeway, arterial, local road, etc.) being considered. Also see scope.

Desire Line
A straight line on a map joining the origin and destination. Desire lines are normally plotted with widths proportional to the trip volumes.

Environmental Impact Statement (EIS)
Report which evaluates the economic, social, and environmental effects of a proposed major transportation project for which federal funding is being sought. Impacts could include air, water, or noise pollution; natural resources; employment effects; displacement of people or businesses; or community or regional growth impacts.

Environmental Protection Agency (EPA)
EPA is the federal source agency of air quality control regulations affecting transportation.

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Expressway
A controlled access, divided highway for through traffic, the intersections of which are usually separated from other roads by differing grades.

Federal Highway Administration (FHWA)
Division of the U.S. Department of Transportation that funds highway planning and programs.

Freeway
A divided highway designed for the unimpeded flow of large traffic volumes. Access to a freeway is rigorously controlled and intersection grade separations are required.

Functional Classification
A method of cataloging a road’s purpose and design. Roads are classified as Interstates, Freeways / Expressways, Arterials, Collectors, and local roads.

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Highway
Term used to describe higher capacity roads; also includes rights of way, bridges, railroad crossings, tunnels, drainage structures, signs, guardrails, and protective structures in connection with highways.

Home Based Work Trip
A trip to or from home for the purpose of one’s employment.

Infrastructure
A term connoting the physical underpinnings of society at large, including, but not limited to, roads, bridges, transit, water and waste systems, public housing, sidewalks, utility installations, parks, public buildings and communications networks.

Interstate System
The system of highways that connects the principal metropolitan areas, cities, and industrial centers of the United States. The Interstate System also connects the U.S. to internationally significant routes in Mexico and Canada. The routes of the Interstate System are selected jointly by the state department of transportation for each state and the adjoining states, subject to the approval of the U.S. Secretary of Transportation.

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Land Use
Refers to how land and the structures (development) on it are used, i.e., commercial, residential, retail, industrial, etc.

Level of Service
A qualitative measure describing operational road (traffic) conditions and the perception of motorists of the existing conditions. Six levels of service are defined for each type of facility, ranging from A to F, with level of service A representing the best operating conditions and level of service F the worst.

Local Street
A street intended solely for access to adjacent properties.

Long Range
In transportation planning, refers to a time span of more that five years. A long-range plan typically covers a twenty-year time span.

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Major Investment
A “high-type highway or transit improvement of substantial cost that is expected to have a significant effect on capacity, traffic, level of service or mode share at the transportation corridor or sub-area scale.”

Metropolitan Planning Organization (MPO)
The organizational entity designated by law with lead responsibility for developing transportation plans and programs for urbanized areas of 50,000 or more in population. MPOs are established by agreement of the Governor and units of general purpose local government, which together represents 75 percent of the affected population or an urbanized area. In the Chicago metropolitan region, the Chicago Area Transportation Study is the designated MPO and covers the six counties of Cook, DuPage, Kane, Lake, McHenry and Will and a portion of Kendall county.

Metropolitan Statistical Area (MSA)
Census Bureau delineation for major metro areas in the U.S. Also includes standard (SMSA) and consolidated metropolitan statistical area (CMSA).

Mobility
The ability to move or be moved from place to place. Typically, mobility is the ease with which movement can occur between geographic areas or parts of the region.

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Mode, Intermodal, Multimodal
Form of transportation, such as automobile, transit, bicycle and walking. Intermodal refers to the connections between modes and multimodal refers to the availability of transportation options within a system or corridor.

Model
A mathematical formula that represents the activity and the interactions within a system so that the system may be evaluated according to various conditions: land use, population, households and employment (socio-economic), transportation, or others.

Network
A graphic and/or mathematical representation of multimodal paths in a transportation system.

National Ambient Air Quality Standards (NAAQS)
Federal standards that set allowable concentrations and exposure limits for various pollutants.

Ozone
Ozone is a colorless gas with a sweet odor. Ozone is not a direct emission from transportation sources but rather a secondary pollutant formed when hydrocarbons (HC) and nitrogen oxides (NOx) combine in the presence of sunlight. Ozone is associated with smog or haze conditions. Although ozone in the upper atmosphere protects the earth from harmful ultraviolet rays, ground level ozone produces an unhealthy environment in which to live.

Particulate Matter (PM), (PM 10)
Any material that exists as solid or liquid in the atmosphere. Particulate matter may be in the form of fly ash, soot, dust, fog, fumes, etc. Small particulate matter, or PM 10, is less than 10 microns in size and is too small to be filtered by the nose and lungs.

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Peak Hour
The 60 minute period during which the largest volume of travel is experienced.

Person Trip
A one-way trip made for any purpose, by any (usually vehicular) travel mode, by one person.

Public Authority
A Federal, State, county, town, or township, Indian tribe, municipal or other local government or instrumentality with authority to finance, build, operate, or maintain toll or toll free transportation facilities.

Public Participation
The active and meaningful involvement of the public in the development of transportation plans and improvement programs. Federal transportation legislation regulations require that state departments of transportation and MPOs proactively seek the involvement of all interested parties, including those traditionally under served by the current transportation system.

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Public Road
Any road or street under the jurisdiction of and maintained by a public authority and open to public traffic.

Region
An entire metropolitan area including designated urban and rural sub-regions.

Right-of-Way (ROW)
Usually that land owned by or under the direct control of a transportation system and on which its vehicles operate.

Scope
The vehicle or person carrying capacity and control of a proposed facility (i.e. number of lanes or tracks, length of project, signalization, etc.)

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Screen Line
The number of vehicles on all roads that cross an imaginary line across all of or part of the study area. This provides a snapshot of the magnitude of travel between areas separated by the line.

Transit
Generally refers to passenger service provided to the general public along established routes with fixed or variable schedules at published fares. Related terms include public transit, mass transit, public transportation or paratransit. Transit modes include commuter rail, heavy or light transit, bus, or other vehicles designated for commercial transportation of non-related persons.

Transportation (or Travel) Demand Management (TDM)
Strategies and collective efforts designed to achieve reductions in vehicular travel demand. It general, TDM does not require major capital improvements. It includes ridesharing, land use policies, employer-based measures, and pricing/subsidy policies.

Transportation Improvement Program (TIP)
This is a document prepared by states and MPOs citing projects to be funded under federal transportation programs, typically for a three to five year period. Without TIP inclusion, a project is ineligible for federal funding.

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Transportation Management Area (TMA)
Defined in federal transportation legislation as all urbanized areas over 200,000 in population. Within a TMA, all transportation plans and programs must be based on a continuing and comprehensive planning process carried out by the Metropolitan Planning Organization (MPO) in cooperation with states and transit operators. The TMA boundary affects the responsibility for the selection of transportation projects that receive federal funds.

Travel Time
Customarily calculated as the time it takes to travel from “door-to door.” In transportation planning, the measures of travel time include time spent accessing, waiting, and transferring between vehicles as well as time spent traveling.

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U.S. Department of Transportation (DOT)
The principal direct federal funding and regulating agency for transportation facilities and programs. FHWA and FTA and units of the US DOT.

Urbanized Area
Area that contains a city of 50,000 or more population plus incorporated surrounding areas meeting set size or density criteria.

Vehicle Hours of Travel (VHT)
The sum of time all vehicles spend traveling, calculated most typically over a 24-hour period. This statistic is most commonly summed over some area like county, but can also be calculated for specific routes or trip purposes like work.

Vehicle Miles of Travel (VMT)
A standard area-wide measure of travel activity. The most conventional VMT calculation is to multiply the average length of trip by the total number of trips.

Volume-to-Capacity (V/C)
The number of vehicles that travel on a road divided by the theoretical capacity of the road. Actual road capacity depends on a wide variety of factors such as lane width, pavement condition, total number of lanes, weather conditions, and more.

Zone
The smallest geographically designated area for analysis of transportation activity. A zone typically ranges in size from one to 10 square miles. Average zone size depends on total size of study area.

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