Glossary of Terms

Arterial – Provides the highest level of service at the greatest speed for the longest uninterrupted distance, with some degree of access control.

Average Daily Traffic (ADT) – The average number of vehicles traveling in both directions at a specified location along a roadway.

Capacity Analysis – A traffic study completed to determine the quality of operation of a given transportation facility. The Level of Service (LOS) is the resultant of the traffic study and states the transportation facility’s quality of operation.

Categorical Exclusion (CE) – A classification given to federal aid projects or actions that do not have a significant effect on the environment either individually or cumulatively; and for which neither an environmental assessment nor an environmental impact statement is required. Categorical Exclusions do not require extensive levels of environmental documentation.

Federal Approved Categorical Exclusion (formerly CE II) – A type of a Categorical Exclusion where actions might have the potential to involve unusual circumstances. Examples of unusual circumstances include but are not limited to:

  • Significant environmental impacts
  • Substantial controversy on environmental grounds
  • Significant impact on properties protected by Section 4(f) of the DOT Act or Section 106 of the National Historic Preservation Act
  • Inconsistencies with any Federal, State, or local law, requirement or administrative determination relating to the environmental aspects of the action

Chicago Metropolitan Agency for Planning (CMAP) – CMAP is the official regional planning organization for the northeastern Illinois counties of Cook, DuPage, Kane, Kendall, Lake, McHenry, and Will.  CMAP developed, and now guides, the implementation of GO TO 2040, metropolitan Chicago's first comprehensive regional planning plan in more than 100 years.

Collector – Provides a less highly developed level of service at a lower speed for shorter distances by collecting traffic from local roads and connecting them with arterials.

Community Advisory Group (CAG) – A group made up of community representatives that serve as the focal point for the exchange of information between government entities and the local community. It is made up of representatives of diverse community interests: local government officials, community representatives, property owners and residents, and stakeholders with technical expertise. It assists the Illinois Department of Transportation in making better decisions on transportation related projects that benefit the community and environment.

Control Delay – A component of delay that results from the type of control at the intersection. It is the difference between the travel time that would have occurred in the absence of the intersection control, and the travel time that results because of the presence of the intersection control.

Delay – The difference in time that a vehicle, pedestrian, or bicyclist spends to travel in absence of interruptions compared to the travel time with interruptions. For this element, average control delay is measured, which is expressed in seconds per vehicle. A prevalent component of delay is control delay.

Design Hourly Volume (DHV) – The hourly two-way traffic volume used for analysis and design.

Design Year – The year the proposed improvement accommodates. Roadway improvement projects are typically designed for 20 years or more in the future.

Environmental Studies – The investigations that analyze air quality, traffic noise, community impacts such as relocations and access changes, natural resources including protected species and habitats, cultural resources such as pre-historic and historic sites, and land and water contamination issues to determine potential environmental impacts. The proposed environmental impacts determine the amount of coordination with State and Federal Resource Agencies in the environmental process and which environmental document is to be completed.

Environmental Assessment (EA) - An EAs purpose is to determine if a proposed project will cause significant impact on the environment. It is a precise public document that serves to:

  • Briefly provide sufficient evidence and analysis for determining whether to prepare an Environmental Impact Statement (EIS) or a Finding of No Significant Impact (FONSI)
  • Facilitate preparation of an EIS when one is necessary.

Environmental Impact Statement (EIS) – A detailed written statement prepared for major Federal actions significantly affecting the quality of the human environment, which discusses the environmental impact of the proposed action; any adverse environmental effects which cannot be avoided should the proposal be implemented; alternatives to the proposed action; the relationship between local short-term uses of the human environment and the maintenance and enhancement of long-term productivity; and any irreversible and irretrievable commitments of resources which would be involved in the proposed action should it be implemented.

Expressways – Divided highways that provide maximum mobility with limited access. These roadways are designed for high speed travel and access occurs at an interchange.

Federally Funded/Regulated – A project that includes Federal funds and/or jurisdictional authority by any Federal agency for a proposed improvement.

Functional Classification – The process by which streets and highways are grouped into classes, or systems, according to the character of traffic service that they are intended to provide. There are three highway functional classifications: arterial, collector, and local roads.

GO TO 2040 – The comprehensive regional plan to help the seven counties and 284 communities plan together for sustainable prosperity through mid-century and beyond.

Highway Capacity – The maximum number of vehicles that can travel through an intersection or section of roadway during a given time period. It is measured in vehicles per hour and is influenced by traffic conditions and geometric design of the roadway.

Lead Agency – The agency responsible for preparing the environmental and design documents.

Level of Service (LOS) – A qualitative concept developed to grade congestion as perceived by motorists, pedestrians, and bicyclists. This concept has been divided into letter descriptions, A through F. The letter descriptions are linked to quantitative measures based on the delay experienced on a roadway segment or at an intersection. Level A represents the best conditions and Level F the worst.

Local Streets – Consists of all roads not defined as arterials or collectors; primarily provides access to land with little or no through movement.

Metropolitan Water Reclamation District of Greater Chicago – The MWRD consists of seven water reclamation plants that treat residential and industrial wastewater. Its service area is 883.5 square miles of Cook County, Illinois. MWRD routinely monitors all industries and non-residential sources to assure that wastes are disposed of in an environmentally responsible and lawful manner.

Mitigation Measures – Actions intended to decrease the severity of an environmental impact precipitated by the proposed action deemed to be unavoidable in the environmental process.

National Environmental Policy Act (NEPA) – Legislation that requires federal agencies to integrate environmental values into their decision-making processes by considering the environmental impacts of their proposed actions and reasonable alternatives to those actions.

Peak Hour – The hour in which the maximum traffic volume occurs on a particular roadway. Typical peak hours that are analyzed are the A.M. peak hour, P.M. peak hour, and/or a weekend peak hour.

Project Study Group – A group consisting of representatives from the County, State, and Federal Agencies, and the project consultant. The group is responsible for the technical guidance and completing the project’s environmental process.

Regulatory Floodway – The channel of a river or other watercourse and the adjacent land areas, which must be reserved in order to discharge the base flood without cumulatively increasing the water surface elevation more than a designated height. Communities must regulate development in these floodways to ensure that there are no increases in upstream flood elevations.

Right-of-Way – Government property used for the construction and use of public facilities like a roadway or utility.

Section 4(f) Land – Any publicly owned park, recreational area, wildlife and waterfowl refuge, or historic site of national, State, or local significance that is protected under 49 USC 303 (Section 4(f) of the USDOT Act of 1966).

Section 6(f) Lands – Lands or facilities which were purchased or developed by Land and Water Conservation (LAWCON) funds.

Stakeholder – Stakeholders for a project include any person or organization which has a direct stake in the project being considered.

Strategic Regional Arterial (SRA) – A roadway intended to carry larger volumes of traffic at higher speeds as a complement to the region's expressway system. Efforts are made to preserve the level of service on these roadways through appropriate access and traffic signal locations and spacing. To ensure a high level of service for traffic on the SRA system, the Illinois Department of Transportation maintains more restrictive criteria in determining the need for and spacing of traffic signals and access points.

Wetlands (Federal) – Those areas inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas.

Wetlands (Illinois) – Land that has a predominance of hydric soils (soils which are usually wet and where there is little or no free oxygen) and that is inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and that under normal circumstances does support, a prevalence of hydrophytic vegetation (plants typically found in wet habitats) typically adapted for life in saturated soil conditions. Areas which are restored or created as the result of mitigation or planned construction projects and which function as a wetland are included within this definition even when all three wetland parameters are not present.