Air Quality

Air pollution is derived from numerous sources. These include: stationary sources such as power plants, large industrial sources, metals, and chemical processing as well as small businesses such as print shops, gas stations, and dry cleaning shops; mobile sources including cars, trucks, buses, planes, trains, as well as construction and lawn equipment; natural sources such as dust, volcanoes or fires including forest and wild fires, controlled burns such as prairies; and finally, other combustion sources including furnaces in our homes, plants, and fires from wood-burning fire places, etc. All these sources contribute to and release different pollutants and incomplete combustion emissions into the atmosphere. The chart below depicts the air pollutants by emission category.

Source: U.S. EPA, Our Nation’s Air Status and Trends Through 2008, February 2010.
*(Particulate Matter (PM); Ammonia (NH 3); Sulfur Dioxide (SO 2); Nitrogen Oxides (NO x); Volatile Organic Compounds (VOC); Carbon Monoxide (CO)) 

Air emissions from these source categories are regulated by the U.S. Environmental Protection Agency (U.S. EPA) and state and local air agencies. U.S. EPA has developed health-based air standards which are known as the National Ambient Air Quality Standards (NAAQS) for six criteria pollutants. These include: carbon monoxide, lead, nitrogen dioxide, particulate matter (PM2.5 and PM10), ozone, and sulfur oxide.

According to the Federal Highway Administration (FHWA), “Transportation contributes to four of the six criteria pollutants: ozone, carbon monoxide, particulate matter, and nitrogen dioxide.” Currently in Illinois, two areas of the State do not achieve the NAAQS for the 8-Hour ozone standard and PM2.5 annual standard: the Chicago Metropolitan Area and the Metro East St. Louis area. The exhibits below depict Illinois’ PM2.5 and ozone 8-hour non-attainment areas. The Illinois EPA Annual Air Quality Report includes additional information.


To fulfill specific air quality requirements under the Clean Air Act (CAA), IDOT partners and works closely with the U.S. Department of Transportation, U.S. and Illinois Environmental Protection Agency (EPA), and Metropolitan Planning Organizations (MPO), to deal with regional as well as micro-scale air quality issues. To help achieve transportation air quality planning goals and to attain the NAAQS, IDOT works through the inter-agency consultation process to ensure that the Long Range Plans and Transportation Improvement Programs, developed by MPOs, conform with air quality improvement plans.

IDOT also evaluates and documents various micro-scale air quality issues such as carbon monoxide and particulate matter hot-spot analyses, in our environmental documents to fulfill National Environmental Policy Act (NEPA), CAA, and other air quality requirements. Chapters 24 to 26 of the Bureau of Design and Environment (BDE) Manual outlines various highway-related air quality issues that are documented in IDOT NEPA documents. 

In addition, air quality emissions from construction-related activities are also addressed. To address potential dust concerns, Dust Control requirements are outlined in IDOT’s Standard Specifications for Road and Bridge Construction.

IDOT has developed additional construction-related specifications and contract special provisions dealing with the use of cleaner diesel fuel, idling reduction requirements for construction equipment, and the installation of emission control devices on contractor vehicles. Construction air quality specifications (cleaner diesel fuel and idling reduction requirements) are contained in Article 107.41 of the Standard Specifications for Road and Bridge Construction.

IDOT has also included a special provision for the installation of emission control devices on contractor vehicles.

IDOT has also sponsored various Air Quality meetings and Peer Exchanges to discuss emerging air quality issues and state-of-the-art air quality practices. Representatives from state DOT’s, FHWA, MPOs, U.S. and Illinois EPA have attended and participated in these meetings. Proceedings from these meetings are provided below:

Water Quality

IDOT maintains approximately 60,000 bridges over streams and rivers. During the construction or rehabilitation of bridge structures, IDOT must comply with the Clean Water Act, the National Environmental Policy Act (NEPA), the Fish and Wildlife Coordination Act, and other related laws and regulations. To comply with these regulations IDOT conducts environmental surveys. These field surveys range from the identification of federal and state listed endangered and threatened species to the characterization of the physical (substrate), biological (fish, mussels, aquatic macroinvertebrates), and chemical (concentrations of heavy metals, chloride, dissolved oxygen) components of streams. The results of these surveys are used to obtain permits (section 404 and 401 of the Clean Water Act) from the Corps of Engineers, Illinois Environmental Protection Agency (IEPA) and/or to meet the requirements of NEPA.

IDOT looks at rivers on the National Wild and Scenic River System and the Nationwide Rivers Inventory and coordination may occur for work on these streams with the National Park Service. IDOT uses IEPA Illinois Integrated Water Quality Report and Section 303(d) List to determine streams or lakes water quality standards, the designated uses of these water bodies, and the IEPA assessment of these uses.

Highways may impact water quality through storm water runoff. IDOT is involved in activities to control and reduce contamination from highway runoff (see Storm Water Management Program on this website). Deicing materials used for snow and ice removal flow into area streams via roadside ditches and/or storm sewers. In addition, a portion of road salt that remains on the pavement may be dispersed into the air due to the motion of traffic. In order to analyze atmospheric dispersal of salt, IDOT, in conjunction with the Illinois State Tollway Authority and the Federal Highway Administration initiated studies that were performed by the Illinois Water Survey.

The 1987 Illinois Groundwater Protection Act was implemented to protect groundwater resources from degradation. The Act allows for the establishment of both regulated groundwater recharge areas and groundwater protection areas. For transportation projects groundwater is assessed in terms of recharge areas to identify the potential for proposed highway corridors to contaminate shallow aquifers. Groundwater studies using monitoring wells are often performed in areas that are considered sensitive because they support plant communities containing endangered or threatened species or land areas that have been designated as Natural Areas or Nature Preserves. Potential impacts to these resources can involve interruption and/or change in groundwater flow patterns. Areas featuring karst topography are especially subject to groundwater contamination because these areas do not contain the usual filtering layers provided by soil so that surface water contamination can flow directly into the groundwater.

An aquifer is an area containing saturated (with groundwater) soils and geologic materials that are sufficiently permeable to readily yield economically useful quantities of water to wells, springs, or streams under ordinary hydraulic gradients. A sole-source aquifer is one which supplies at least 50 percent of the drinking water consumed in the overlying area with no practicable alternative drinking water source. While Illinois has no designated sole-source aquifer at the present time, it has many shallow (sand and gravel) and deep (bedrock) aquifers. Public well water supplies are regulated through set back zones established by IEPA.

Every two years the IEPA issues an “Illinois Integrated Water Quality Report and Section 303(d) List”. Information on groundwater standards and groundwater quality can be found in this report.

Floodplains are areas of land that could be inundated by floodwaters from any source. Floodplains usually occur adjacent to streams, rivers, and lakes. Transportation projects are assessed for the potential for impacts to floodplains, more specifically encroachments into the 100-year floodplain. The 100-year floodplain is defined as an area that has a 1 percent or 1 chance in 100 of experiencing a flood condition that exceeds any previous 1 year period. Coordination with the U.S. Army Corp of Engineers and the Department of Natural Resources Office of Water Resources (IDNR-OWR) is required to obtain the necessary permits for work within floodplains. A regulated floodway is the channel of the stream plus any adjacent floodplain areas. These areas must be kept free of encroachment so that the 1 percent chance annual flood can occur without substantial increases in flood heights. Depending upon the location of the regulated floodplain, the regulatory authority may be the community within which the floodway is located, FEMA or IDNR-OWR. Bridge structures located over major rivers such as the Mississippi must be coordinated with the U.S. Coast Guard to ensure that pier placement does not affect shipping channels.


IDOT assesses potential impacts to wildlife and their habitats while planning and designing transportation facilities. To comply with the National Environmental Protection Act and other state and federal environmental laws and regulations, special studies and assessments are conducted, and coordination with state and federal natural resource agencies is initiated. Project impacts to wildlife are identified and evaluated and consideration is given to implementing practical measures to avoid, minimize, and mitigate any adverse impact to these valuable resources. To accommodate wildlife connectivity and to increase safety to the motoring public, IDOT includes wildlife crossing structures such as underpasses, culvert extension, and fencing within project designs in environmentally sensitive locations that feature quality habitat. These measures not only reduce wildlife mortality and the number of vehicle-animal collisions but help to ensure that species populations remain viable. In addition, IDOT considers effects on area sensitive migratory birds during project development and evaluates the potential for habitat fragmentation.

IDOT is one of many state and local agencies, and environmental groups involved in the “Illinois Wildlife Action Plan.” This initiative was developed to address the particular needs of wildlife species in an effort to stabilize and reverse trends in declining populations. The plan can be accessed here.

Other sources of information about this topic include:

  • The 2006 publication “Eco-Logical: An Ecosystem Approach to Developing Infrastructure Projects” is a guide for making infrastructure more sensitive to wildlife and ecosystems through greater interagency cooperation. More information on the “Eco-Logical” approach can be found here.
  • “The North American Breeding Bird Survey” is a major landscape-level survey of the birds of North America. It is an on-going cooperative program sponsored jointly by the U.S. Fish and Wildlife Service and the Canadian Wildlife Service. The main purpose of this roadside survey is to estimate population trends of the many species of birds that nest in North America and migrate across international boundaries. More information can be found on the U.S. Fish & Wildlife Service website or the North American Breeding Bird Survey page.
  • The Illinois Natural History Survey website contains extensive information regarding all aspects of vertebrate and invertebrate species in Illinois. The “Inventory of Resource Rich Areas,” a watershed based land cover survey that identifies areas within the state that contain high quality habitat such as large tracts of woodlands and nearly one-half of the remaining wetlands can be found on the Illinois Natural History Survey Research webpage.
  • Information regarding wildlife – vehicle collisions can be found on the Deer Vehicle Crash Information Clearinghouse webpage. This national study details the causes and impacts to wildlife-vehicle collisions. The site is a deer crash information clearinghouse that contains accident data and suggested countermeasures and strategies to reduce the number of deer-vehicle accidents.

Threatened and Endangered Species

Under the Endangered Species Act of 1973 and the Illinois Endangered Species Act, IDOT is required to consult with the U.S. Fish and Wildlife Service (U.S. FWS) and the Illinois Department of Natural Resources (IDNR) to insure that the department’s projects are not likely to jeopardize the continued existence of any endangered and threatened species (listed species). IDOT Division of Highways, Bureau of Design and Environment (BDE) procedures for consulting with the U.S. FWS and IDNR on these two Acts are detailed in Chapters 26 (section 26-9) and 27 (section 27-1) of the BDE manual.

The department utilizes in-house expertise together with other sources of geographic information to screen project areas for the presence of habitats that may contain or be suitable for a listed species. In the event a listed species is present or there is suitable habitat within a project area, IDOT will conduct surveys through a statewide contract with the Illinois Natural History Survey (INHS) to determine the continued presence of the species and suitable habitat in the area which aids the department in avoiding impacts, minimizing impacts, and as a last case scenario mitigating impacts. More information can be found on the INHS website.

There are occasions where the department will request INHS through the statewide contract to conduct surveys throughout the state or a specific region to gather more data to further streamline consultation with the agencies. One example of that is the survey work performed in District 1 for the Indiana bat. More information can be found under the Indiana Bat (below).

Indiana Bat

IDOT’s BDE, Illinois State Toll Highway Authority, and Chicago office of the U.S. FWS developed a plan in 2006 for a mist-netting survey in northeastern Illinois to determine if the federally endangered Indiana Bat (Myotis Sodalis) occurs in the region. The U.S. FWS staff produced a list of 20 survey areas, primarily in public ownership, in Cook, DuPage, Kane, Kankakee, Lake, McHenry, and Will counties that were deemed to provide high-quality summer habitat for the Indiana Bat. Most of these areas included multiple netting sites. INHS conducted the survey during the summers of 2006 and 2007. Mist netting was conducted for 87 nights at 43 sites. This represented a 176 net-nights of effort (1 net-night = 1 net checked for one night). Following this effort, no Indiana Bats were captured by the INHS. The Indiana Bat collected in Chicago in September 1928 remains the only record for the area. Results of the 2006-2007 survey suggest that the Indiana Bat is extinct from the northeast corner of the state. Survey results will be used by the U.S. FWS to clear a number of transportation projects over the next several years that involve impacts to suitable habitat for the Indiana Bat.

Below are the results for the 2006 and 2007 mist netting surveys:

Further Information

Web Links

  • Bureau of Design and Environment Manual



IDOT complies with Section 404 of the Clean Water Act (CWA) and the Illinois Interagency Wetland Policy Act of 1989 (IWPA). Departmental procedures for ensuring compliance with the CWA and IWPA are detailed in the IDOT Wetlands Action Plan, Bureau of Design and Environment Manual, Chapter 26-8. Under the CWA and IWPA, IDOT must demonstrate that all measures were taken to first avoid and then minimize impacts to wetlands to the fullest extent practicable. Unavoidable impacts are mitigated by way of wetland compensation through either restoration or creation of wetlands.

IDOT. The INHS and Illinois State Geological Survey provide technical assistance to IDOT in locating, evaluating and monitoring compensatory wetlands. More information on the Wetlands Group can be found on INHS’s Wetland Science Program webpage.

IDOT Wetland Compensation Sites

County Site Name Route and FAP # ISGS# Status
Alexander East Cape Girardeau IL 146, FAP 312 81 Active
Coles I-57/TR1000N Interchange TR1000N, TR41 N/A Active
Effingham Green Creek IL33, FAP 774 75 Active
Franklin Sugar Camp Creek IL 3, FAP 312 74 Inactive
Hancock Hancock County near Carthage US 136, FAP 315 & 10 42 Active
Henderson Gulfport US 34, FAP 313 29 Inactive
Henry Joslin IL 92, FAP 585 23 Inactive
Jackson Carbondale US 51, FAP 332 65 Inactive
Jackson De Soto US 51, FAP 332 68 Inactive
Jo Daviess Galena River Bridge, West Stagecoach Trail FAS 67 46 Inactive
Johnson Max Creek IL 147, FAS 932 80 Active
Lake North Chicago IL 47, FAP 326; IL 56, FAP 365 N/A Active
Macon Decatur US 51, FAP 322 27 Active
Madison Sand Road US 267, FAP 310 15 Inactive
Madison Former Luehmann Property, New River Crossing FAP 999 51 Inactive
Mercer Edwards River, Mercer County US 67, FAP 310 50 Inactive
Perry Pyatts Blacktop IL 13 & 127, FAP 42 67 Inactive
Perry Swan Road TR 222 86 Active
Pike Hannibal Bridge US 36, FAP 319 10 Inactive
Rock Island Milan Beltway, Airport Road FAU 5822 17 Active
Rock Island Milan Beltway, Phase 1 Green Rock FAU 5822 44 Active
Rock Island Milan Beltway, Phase 2 Green Rock FAU 5822 44 Inactive
Rock Island Milan Beltway, Rock Island Site FAU 5822 N/A* Active
Saline Harrisburg US 45, FAP 332 63 Active
Saline Harrisburg, Site 2 IL 14, FAP 857 N/A* Active
Saline Harrisburg Site 3 IL 13, FAP 331 N/A* Active
Saline Saline County IL 13, FAP 331 18 Active
Sangamon Veteran’s Parkway, Springfield FAP 662 9 Inactive
Sangamon Springfield IL 29, FAP 658 54 Inactive
Sangamon Buckhart TR 478, FAS 1637 58 Inactive
Stephenson Orangeville IL 26, FAP 316 16 Inactive
Stephenson Jane Addams Trail US 20, FAP 301 72 Active
Stephenson Weber Property N/A 79 Active
Union Tamms IL 127, FAS 1907 71 Active
Will Grant Creek North I-55, FAI 55 N/A* Active
Winnebago Pecatonica River Forest Preserve Harrison Avenue Extension 73 Inactive

Wetland Mitigation Bank Sites

The link below will provide electronic copies of base-line studies, instruments and monitoring reports for IDOT bank sites and multi-use compensation sites.

IDOT Wetland Mitigation Bank Sites

Further Information

Web Links

Roadside Maintenance

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