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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.
Air Quality
The cleanliness of the air; the fewer pollutants in the air, the better the air quality.
The route that an improvement could take through a corridor.
An alternative includes various improvements (modal options) designed to address transportation deficiencies in the project area.
An arterial roadway serves major traffic movements or major traffic corridors. While they may provide access to abutting land, their primary function is to serve traffic moving through the area.
Average Daily Traffic (ADT)
The total volume of traffic in both directions on a highway during a time period of greater than one day but less than a year, then divided by the number of days for which traffic data were collected.


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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 Action
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.
Bureau of Design & Environment (BDE)
The Illinois Department of Transportation, Division of Highways Bureau of Design & Environment, ensures that all department and consultant personnel preparing Phase I studies and reports and contract plans for the department are carried out by following prescribed uniform criteria.


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The maximum amount of traffic on any transportation facility that can be accommodated and still function.
Chicago Metropolitan Agency for Planning (CMAP)
Formed in 2005, CMAP integrates planning for land use and transportation in the seven counties (Cook, DuPage, Kane, Kendall, Lake, McHenry, and Will).of northeastern Illinois. The new organization combined the region's two previously separate transportation and land-use planning organizations -- Chicago Area Transportation Study (CATS) and the Northeastern Illinois Planning Commission (NIPC) -- into a single agency.
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.
Consensus is defined as a majority of the stakeholders in agreement, with the minority agreeing that their input was duly considered.
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.
Context Sensitive Solutions (CSS), IDOT program
An interdisciplinary approach that seeks effective, multimodal transportation solutions by working with stakeholders to develop, build and maintain cost-effective transportation facilities which fit into and reflect the project's scenic, economic, historic, and natural surroundings.
Cooperating Agencies (CA)
Per the National Environmental Policy Act (NEPA), a cooperating agency is any federal agency that has jurisdiction by law or special expertise with respect to any environmental impact involved in a proposed project. Cooperating agencies are permitted, by request of the lead agency, to assume responsibility for developing information and preparing environmental analyses for topics about which they have special expertise.
A corridor is a general path from one point to another.
Corridor Advisory Group (CPG)
Interactive group made up of elected officials representing stakeholders that are directly affected by the project, and who have authority to enter into intergovernmental agreements.


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Descriptive characteristics of populations. Examples include age, race and ethnicity, gender, income, employment and household status.
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.
Draft Environmental Assessment (DEA)
A Draft Environmental Assessment (DEA) is a document submitted to the FHWA in order to comply with the NEPA process. The DEA is a study of land to determine any unique environmental attributes, considering everything from endangered species to existing hazardous waste to historical significance.


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Surrounding conditions or circumstances. Usually used as a reference to nature (the natural environment) but also can include man-made conditions (the built environment).
Environmental Assessment (EA)
A study of land to determine any unique environmental attributes, considering everything from endangered species to existing hazardous waste to historical significance.
Environmental Factors
In transportation, these factors include air, water and living (eco)systems, as well as community and social factors such as aesthetics/visual, archeology, culture, economics, history and noise.
Environmental Mitigation
Methods, strategies or actions to reduce the negative effects, direct, indirect and cumulative, of a transportation project on the environment.
Environmental Protection Agency (EPA)
EPA is the federal source agency of air quality control regulations affecting transportation.
Evaluation Criteria
A standard or measure that permits a comparative evaluation of an alternative.


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Any death on the transportation system that occurs as a result of a moving vehicle.
Federal Highway Administration (FHWA)
Division of the U.S. Department of Transportation that funds highway planning and programs.
A calculation or estimate of future conditions.
Commercial goods carried by a vehicle, usually a truck, plane, train or ship; cargo.
Functional Classification
A method of cataloging a road’s purpose and design. Roads are generally classified as Interstates, Freeways / Expressways, Arterials (principal or minor, urban or non-urban), Collectors (major or minor, urban or non-urban), and local roads (urban or non-urban).


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Geographic Information Systems (GIS)
A computer software tool that is used to solve problems based on geographically related information. It is a system linked to a graphics system capable of collecting, storing, analyzing and manipulating spatial information.


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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.


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Illinois Department of Natural Resources (IDNR)
Illinois Department of Natural Resources (IDNR) is a State Agency that manages, protects and sustains Illinois' natural and cultural resources; provide resource-compatible recreational opportunities and to promote natural resource-related issues for the public's safety and education.
Illinois Department of Transportation (IDOT)
The Illinois Department of Transportation has responsibility for planning, construction and maintenance of Illinois' extensive transportation network. This network encompasses highways, bridges, airports, public transit, rail freight and rail passenger systems.
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.
A multilevel highway intersection arranged so that vehicles may move from one road to another without crossing streams of traffic.
A point at which separate roadways cross, meet, or overlap.


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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. Initially used to define the road network, the concept has been expanded to include bicycle and pedestrian conditions.
Local Street
A street intended solely for access to adjacent properties.
Long Range Transportation Plan (LRTP)
In transportation planning, typically covers a twenty-year time span. Projects expecting to use federal funding must be included in the LRTP.


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Metra provides commuter rail service in the Chicago Metropolitan area. Metra, with 495 miles of track, serves 230 stations in the counties of Cook, DuPage, Lake, Will, McHenry and Kane.
Metropolitan Planning Organization (MPO)
Formed in cooperation with the state, the Metropolitan Planning Organization (MPO) develops transportation plans and programs for the metropolitan area. For each urbanized area, an MPO must be designated by agreement between the Governor and local units of government representing 75% of the affected population (in the metropolitan area), including the central cities or cities as defined by the Bureau of the Census, or in accordance with procedures established by applicable State or local law. The MPO for the Chicagoland area is Chicago Metropolitan Agency for Planning (CMAP).
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.
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.
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.
Moving Ahead for Progress in the 21st Century Act (MAP-21)
The federal transportation law enacted in 2012 that guides and funds the various programs that affect the nation’s transportation system. Previous laws were the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU) in 2005 and Transportation Equity Act for the 21st Century (TEA-21) in 1998.


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National Ambient Air Quality Standards (NAAQS)
Federal standards that set allowable concentrations and exposure limits for various pollutants.
National Environmental Policy Act (NEPA)
NEPA guides federally funded projects and projects that require a Federal permit to lessen potential damages to the environment. The NEPA process requires federal agencies to integrate environmental values into their decision-making process by considering the environmental impacts of their proposed actions and reasonable alternatives to these actions. Environmental factors such as air quality, wildlife, vegetation, water quality, wetlands, geology, neighborhoods, park/recreation areas, utilities, visual quality, and cultural resources will be assessed. NEPA encourages early and frequent coordination with the public and resource agencies throughout the project development process. Public comments that are received during the alternative analysis phase are considered in the draft environmental document. Following NEPA guidelines, a document called an Environmental Assessment will be prepared. The process calls for continuous environmental evaluations as alternatives are analyzed.
A graphic and/or mathematical representation of multimodal paths in a transportation system.


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Operations, Operational Strategies
How a transportation network functions; operational strategies are techniques that influence how a network functions. For example, traffic signals and signs are operational activities that control traffic.
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.


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Pace primarily provides bus service in suburban areas outside the City of Chicago.
Park and Ride Facility
An access mode to transit in which patrons drive private automobiles or ride bicycles to a transit station, stop, or carpool/vanpool waiting area and park their vehicle in the area provided for park and ride patrons. They then ride the transit system or take a carpool or vanpool to their destinations.
Participating Agencies
Per MAP-21, a participating agency is any federal, state, tribal, regional, and local government agency that may have an interest in the project. By definition, all cooperating agencies will also be considered participating agencies. However, not all participating agencies will serve as cooperating agencies.
Peak Hour
The 60 minute period during which the largest volume of travel is experienced.
Peak Travel Period
The period in the morning (a.m. peak period) and afternoon or evening (p.m. peak period) when additional transportation services are needed/provided to handle higher traffic/passenger volumes. The period begins when normal travel times increase and ends when travel times return to normal. In the Chicago metropolitan area, the a.m. peak period is generally 6:00 a.m. to 8:00 a.m. and the p.m. peak period is 4:00 p.m. to 6:00 p.m. each weekday.
Person Trip
A one-way trip made for any purpose, by any (usually vehicular) travel mode, by one person.
Project Study Group (PSG)
The working group for a project will consist of a Project Study Group (PSG). The PSG will make the ultimate project recommendations and decisions on this project and the membership of the PSG will evolve as the understanding of the project’s context is clarified. Other responsibilities of the PSG include the expediting the project development process, identifying and resolving project development issues, promoting partnership with stakeholders to address identified project needs and working to develop consensus among stakeholders.
Public Authority
A Federal, State, county, town, 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 MPO’s proactively seek the involvement of all interested parties, including those traditionally underserved by the current transportation system.
Public Road
Any road or street under the jurisdiction of and maintained by a public authority and open to public traffic.
Public 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 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.
Purpose and Need
The Purpose and Need in an environmental document presents why the proposed action, with its inherent costs and environmental impacts, is being pursued.


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Quality of Life
A term used to describe the lifestyle conditions of an area. Conditions include the scale and depth of opportunities or choices in housing, employment, transportation, the natural environment, education, health care, and recreational and entertainment activities.


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An entire metropolitan area including designated urban and rural sub-regions.
Regional Transportation Authority (RTA)
The Regional Transportation Authority, created in 1973, oversees the operation and funding of public transit in the Chicago metropolitan area. There are three service boards under the RTA—the Chicago Transit Authority (CTA), Metra and Pace.
Right-of-way (ROW)
The land (usually a strip) acquired for or devoted to transportation purposes.


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A term used to describe social and economic factors, generally resulting from an analysis of demographics of a population.
Stakeholder Involvement Plan (SIP)
The SIP is a blueprint for defining methods and tools to educate and engage all stakeholders in the decision-making process for a project. The SIP provides the framework for achieving consensus and communicating the decision-making process between the general public, public agencies, and governmental officials to identify transportation solutions for the project.


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Technical Advisory Group (TAG)
The technical advisory groups (TAG) provide a means for obtaining structured input from a diverse set of stakeholders.
Traffic Analysis Zone
In planning, a division of a study area that is represented by a centroid and used for traffic assignment purposes.
Traffic Controls
Traffic control systems are designed to reduce travel times, delays and stops, while also improving the average speed on arterial roadways and freeways. These systems include elements such as coordinated traffic signals, continuous optimization of timing plans, use of bus priority signal control systems, and implementation of computer-based traffic control and freeway traffic management.
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. In 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 MPO’s 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.
Transportation Network
Arrangement of transportation systems for the movement of passenger and cargo. Transportation systems include grid systems, radial networks, circumferential networks and assorted networks.
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.
Transportation System Management (TSM)
Current TSM practices are fundamental traffic engineering actions taken to improve the operation of the highway system. TSM actions are usually categorized as "supply-side" (actions intended to increase the existing vehicle capacity on the system) and "demand-side" (actions that are designed to reduce vehicle demand on the system by increasing vehicle occupancy). For example:
Travel Demand Modeling
Travel demand modeling or travel forecasting is a major step in transportation planning. This is the process by which trip assignments are made to roadways, transit, and high-occupancy vehicles.
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 (USDOT)
The principal direct federal funding and regulating agency for transportation facilities and programs. FHWA and FTA are agencies in the USDOT.
Urbanized Area
Area that contains a city of 50,000 or more population plus incorporated surrounding areas meeting set size or density criteria.


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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.


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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.