Air Quality Impacts


High levels of ozone and fine particulates have been a persistent issue for the OKI region, often exceeding national air quality standards. Vehicle emissions are a major contributor to ozone and particulates, and are a major consideration in transportation planning. Individual vehicle trips may seem insignificant, but their cumulative effect is a major determinant of an area’s air quality.

Impact Assessment

The air quality impacts of the 2040 Plan have been forecasted using OKI’s Travel Demand Model and EPA’s Emissions Model. The Plan, through recommendations to increase transit availability, improve traffic operations and reduce roadway bottlenecks, will result in:

  • Fewer vehicle emissions of ozone-forming volatile organic compounds (VOC) and oxides of nitrogen (NOx).
  • Fewer emissions of greenhouse gases (expressed as carbon dioxide equivalent).

Improvements to vehicle technology, as required by federal regulations, are the primary reason for the dramatic improvement in future vehicle emissions. The states of Ohio and Kentucky have also implemented regulations specifically aimed at vehicle emission reductions. During the summer months, a cleaner-burning gasoline is sold throughout all of OKI’s Ohio and Kentucky counties.

Regional Commitment to Clean Air

Air quality continues to be a key criterion for OKI in making decisions for transportation plans, programs and projects. In addition to capital improvement to the transportation system, the OKI 2040 Plan has recommended behavior based strategies to reduce vehicle miles traveled. These travel demand management (TDM) strategies encourage using alternatives to SOV travel and shifting trips out of peak travel period, or even eliminating some trips all together. OKI’s Regional Clean Air Program continues to market its successful “Do Your Share For Cleaner Air” campaign that provides valuable information to the community, businesses and the media on air quality topics.

Regional Air Quality Status

Daily Emissions

Daily Emissions from Transportation Sources (tons per day)
2040 Base
2040 Plan
Volatile Organic Compounds (VOC)
Oxide of Nitrogen (NOx)
Fine Particles (PM2.5)
CO2 Equivalent (greenhouse gases)

Transportation Conformity

In May 2012, pursuant to provisions of the Clean Air Act Amendments of 1990, the U.S. Environmental Protection Agency (EPA) designated nine counties in the Cincinnati area as a marginal nonattainment area for ozone under the 2008 ozone standard.

U.S. EPA has designated seven counties as a maintenance area under the 1997 annual fine particulate (PM2.5) standard. The region is in attainment for all other criteria pollutants monitored by U.S. EPA.

All nonattainment and maintenance areas are subject to transportation conformity requirements. OKI is responsible for the air quality conformity determination for the region’s Transportation Plan and Transportation Improvement Program.

This 2040 Plan includes 104 recommended projects, which, due to their scope and regional significance, are subject to transportation conformity requirements (non-exempt projects). A new regional emissions analysis and finding of conformity is required. OKI has determined through a quantitative analysis, the following findings:

  • The implementation of this OKI 2040 Regional Transportation Plan will result in motor vehicle emissions that are consistent with the air quality goals of State Implementation Plans (SIPs). -The region’s ozone forming vehicle emissions do not exceed the established motor vehicle emissions budgets for 2015 through 2040.
  • The region’s motor vehicle emissions of fine particulate matter will not cause or exacerbate exceedances of the fine particulate matter standard.

In addition, OKI qualitatively finds that no goals, directives, recommendations or projects identified in the plan contradict, in a negative manner, any specific requirements or commitments of the applicable SIP. Full details on the regional conformity process and determination may be found in Air Quality Conformity Determination of OKI FY 2016-2019 Transportation Improvement Program and OKI 2040 Regional Transportation Plan in the Cincinnati-Hamilton OH-KY-IN Area for National Ambient Air Quality Standards (NAAQS) Technical Documentation, June 2016.