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CMAQ and Diesel Retrofits

Image of a retrofitted long-haul tractor-trailer traveling down a highway. And an image of a heavy-duty construction vehicle with a diesel particulate filter.

What is CMAQ?

Jointly administered by the Federal Highway Administration (FHWA) and the Federal Transit Administration (FTA), the Congestion Mitigation and Air Quality Improvement (CMAQ) Program provides a flexible funding source for transportation projects and programs that help improve air quality and reduce congestion.

State and local governments can use the funding to support efforts to meet National Ambient Air Quality Standards (NAAQS) under the Clean Air Act in both nonattainment and maintenance areas for carbon monoxide, ozone, and particulate matter.

For a list of nonattainment and maintenance areas, see

The Moving Ahead for Progress in the 21st Century Act (MAP-21) requires that States with designated nonattainment or maintenance areas for small particles, known as fine particulate matter (PM2.5), use a portion of their CMAQ funds for projects to reduce those emissions.

Eligibility Requirements

To be eligible for CMAQ funding, a project must come from a conforming transportation plan and transportation improvement program (in metropolitan areas) or from a State transportation improvement program (in rural areas). State Departments of Transportation (DOTs) are responsible for distributing CMAQ funds. The federal share for most CMAQ-eligible projects is 80 percent, but certain safety projects that include an air quality or congestion relief component (e.g., carpool/vanpool projects), may have a Federal share of 100%. The CMAQ program operates on a reimbursement basis, so funds are not provided until work is completed.

Further, all CMAQ projects must meet these three eligibility requirements:

A diesel particulate filter and an image of a piece of construction equipment retrofitted with a diesel particulate filter.

Diesel particulate filters like these can be installed on many types of vehicles and equipment to reduce emissions.

Why Diesel Retrofits?

Diesel engines play a vital role in key industry sectors including freight, public transportation, construction, and agriculture. However, diesel exhaust contains high levels of PM2.5, which can pose significant risks to public health, including causing lung damage and premature death.

MAP-21 places considerable emphasis on select project types, including diesel retrofits, to reduce PM2.5 emissions. Eligible projects include acquisition of retrofitted vehicles, installation of tailpipe emissions control devices, and provision of diesel-related outreach activities. Typical diesel engines in heavy-duty trucks and equipment can last up to 30 years, and the U.S. Environmental Protection Agency (EPA) estimates that more than 11 million older diesel engines are in use today. Unlike newer models, older engines are highly polluting.

Diesel retrofits offer a cost-effective way to reduce air emissions. The harmful effects of diesel emissions on public health are well-established, and over 45 products are available and EPA-verified for engines built between 1960 and 2006.

CMAQ funds have been used for diesel retrofits on many types of vehicles:

Photo of a street sweeper.

A street sweeper is retrofitted with a diesel particulate filter.

What are the Benefits?

1 Source:

Who Can Participate?

State departments of transportation are responsible for distributing CMAQ funds to metropolitan planning organizations (MPOs) and rural nonattainment and maintenance areas. A public sponsor, such as an MPO, city, county, or school district, is required for each project.

Examples of CMAQ-funded Diesel Retrofit Projects

A diesel particulate filter and an image of a piece of construction equipment retrofitted with a diesel particulate filter.

This refuse truck is outfitted with a diesel particulate filter.

New York City, Refuse Trucks

The New York City Department of Sanitation used CMAQ funds to retrofit approximately 828 refuse trucks. Diesel particulate filters were installed on 616 trucks, while diesel oxidation catalysts were used on the remaining vehicles.

Cost: $10 million over several years

Emissions reductions:

Chicago, Switcher Locomotives

The Chicago Metropolitan Agency for Planning funded the retrofit of seven switcher locomotives at the CSX Barr Rail Yard in Riverdale, IL.

Cost: $9.2 million (with local match provided by CSX)

Emissions reductions:

Image of a retrofitted CSX switcher locomotive.

CMAQ funds helped pay for retrofitting of CSX switcher locomotives like this one.

San Francisco Bay Area, Transit Buses

The Metropolitan Transportation Commission allocated funding to 12 transit agencies in the Bay Area to retrofit nearly 1,700 transit buses with diesel particulate filters.

Cost: $15.6 million ($13.8 million CMAQ; $1.8 million local match)

Emissions reductions:

For more information, please contact:

U.S. Department of Transportation Federal Highway Administration
Office of Natural Environment
1200 New Jersey Avenue, S.E.
Washington, D.C. 20590


This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for use of the information contained in this document. This report does not constitute a standard, specification or regulation.

Quality Assurance Statement

The Federal Highway Administration provides high quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

Publication No. FHWA-HEP-13-011

Updated: 1/31/2017
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