Skip to content U.S. Department of Transportation/Federal Highway AdministrationU.S. Department of Transportation/Federal Highway Administration

Office of Planning, Environment, & Realty (HEP)
PlanningEnvironmentReal Estate

HEP Events Guidance Publications Awards Contacts

Prairie Parkway Study Fine Particulate Matter (PM2.5) Project Level Hot-Spot Analysis

1.0 Executive Summary

The Northeastern Illinois and Northwestern Indiana regions have been designated as nonattainment of the national ambient air quality standard (NAAQS or "standard") for fine particulate matter (PM2.5). Based on the Transportation Conformity regulations found in 40 CFR 93.123(b)(1) (as amended March 10, 2006) federally funded nonexempt transportation projects in the Northeastern Illinois/Northwestern Indiana region are required to address project level or "hot-spot" considerations for PM2.5.

According to 40 CFR 93.123(b)(2) and (4), a quantitative analysis for applicable projects is not required until EPA releases modeling guidance in the Federal Register. However, a qualitative hot-spot analysis is required for projects that are found to be "projects of air quality concern" in order to assess whether the project will cause or contribute to any new localized PM2.5 violations, increase the frequency or severity of any existing violations, or delay timely attainment of the PM2.5 NAAQS. This document addresses those requirements for the Prairie Parkway project.

This analysis used a surrogate methodology for complying with the qualitative hot-spot requirements. A "surrogate" (or substitute) site is a site for which the current levels of Average Daily Traffic (ADT) and truck traffic are comparable to or greater than those of the future worstcase build scenario. If, additionally, the surrogate site has a monitor in the vicinity with current PM2.5 monitored values less than the standards, then one can logically conclude that the worstcase build scenario will not cause or add to an existing PM2.5 violation.

Four surrogate sites with PM2.5 monitors in proximity to existing freeways were chosen for this analysis: Elgin/I-90, Aurora/I-88, Joliet I-80 & I-55 and Braidwood/I-55. At these locations current freeway mainline daily traffic ranges from 30,000 to over 100,000; nearest arterial road interchange daily traffic ranges from 8,000 to over 33,000 and heavy commercial vehicle traffic is between 10% and 24% of total daily traffic. The Prairie Parkway Preferred Alternative forecast traffic ranges from 13,400 to 28,600 (nearterm) and 25,000 to 50,000 (design year) vehicles per day with approximately 20% estimated to be diesel powered vehicles. Current traffic conditions at these four surrogate sites equal or exceed those forecast for the Prairie Parkway Preferred Alternative. The most recent (2004 to 2006) PM2.5 monitor data at these four locations show them to be below both the 24-hour and annual PM2.5 NAAQS.

In summary, current monitor data from four locations with (1) traffic levels equal or higher than those estimated for the Prairie Parkway Preferred Alternative; (2) current development levels comparable to those forecast for the study area; and (3) proximate enough that metrological conditions are equivalent all meet the current PM2.5 24-hour and annual mean NAAQS. Thus, it is determined that the Prairie Parkway Preferred Alternative meets the PM2.5 project-level conformity requirements, and will not cause or contribute to a new violation of the PM2.5 NAAQS, or increase the frequency or severity of a violation.

2.0 Purpose of this Document

The Clean Air Act section 176(c) requires that federally supported highway and transit project activities be consistent with state air quality goals, found in the State Implementation Plan (SIP). The process to ensure this consistency is called Transportation Conformity. Conformity to the SIP means that transportation activities will not cause new violations of the national ambient air quality standards (NAAQS or "standards"), worsen existing violations of the standard, or delay timely attainment of the relevant standard.

Transportation conformity is required for federal supported transportation projects in areas that have been designated by the U.S. Environmental Protection Agency (EPA) as not meeting a NAAQS. These areas are called nonattainment areas if they currently do not meet air quality standards or maintenance areas if they have previously violated air quality standards, but currently meet them and have an approved Clean Air Act section 175A maintenance plan.

EPA amended the Transportation Conformity rule on March 10, 20061 requiring a hot-spot analysis to determine project-level conformity in PM2.5 and PM10 nonattainment and maintenance areas. A hot-spot analysis is an assessment of localized emissions impacts from a proposed transportation project and is only required for "projects of air quality concern." The March 10, 2006 rule provides examples of projects of air quality concern. The PM2.5 and PM10 hot-spot requirements in the final rule became effective April 5, 2006. Project level hot-spot analyses are required pursuant to 40 CFR Part 93.

The Prairie Parkway project is partially located within the Metropolitan Chicago Interstate Air Quality Control Region (AQCR #67). The portion of the project from I-88 south to the Kane/Kendall border (approximately 10 miles) and where preferred alternative connects to I-80 near Minooka in Aux Sable Township of Grundy County are within AQCR #67. This region is currently designated as a nonattainment area for the ozone and PM2.5 NAAQS2. Early interagency coordination on the project involving IDOT, FHWA, USEPA, IEPA and CMAP resulted in the determination that the Prairie Parkway project is a project of air quality concern, and thus a qualitative hot-spot analysis has been completed for the project. This hot-spot analysis of the Prairie Parkway Preferred Alternative follows the joint EPA/FHWA guidance for qualitative PM hot-spot analysis3.



1 EPA posted the final rule on its website on March 1, 2006 and the final rule was published in the Federal Register on March 10, 2006.
2 EPA: Last updated on Wednesday, March 15, 2006; URL: http://www.epa.gov/oar/oaqps/greenbk/
3 EPA/FHWA, "Transportation Conformity Guidance for Qualitative Hot-spot Analyses in PM2.5 and PM10 Nonattainment and Maintenance Areas", March 2006.
Updated: 07/06/2011
HEP Home Planning Environment Real Estate
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000