Congestion Mitigation and Air Quality (CMAQ) program

Policy Issue

Congestion Mitigation and Air Quality Program (CMAQ)

The Congestion Mitigation and Air Quality (CMAQ) program, co-administered by Federal Highway Administration and the Federal Transit Administration was created to help off-set the adverse impact on air quality from additional traffic generated by new and expanded road projects. CMAQ funds are allocated from the Federal Highway Trust Fund to assist states with “nonattainment areas.” These funds can be used in concert with transportation projects to either reduce traffic congestion, improve air quality, or both. For more information on the history of the CMAQ program, please click here.

As part of the 2005 Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU), Congress acted to:

  1. Allow states to use CMAQ funds to reduce pollution from road construction equipment.

  2. Build on the success of emission control projects like the one employed during the Big Dig. The Big Dig site in Boston is the prototype for emission reductions at a construction site. The impact of diesel pollution was minimized at the site by retrofitting construction equipment and limiting idling time. Preliminary estimates of area-wide emission reductions from just the retrofitting of equipment amounted to approximately 36 tons per year of carbon monoxide (or the equivalent of entirely removing more than 75 newer model cars from use each year), 12 tons per year of hydrocarbons (or the equivalent of entirely removing more than 350 newer model cars from use each year), and 3 tons per year of particulate matter (or the equivalent of entirely removing more than 270 newer model cars from use each year). Moreover, the Big Dig experienced no adverse operational problems or additional maintenance costs related to its emission reduction strategies.

  3. Provide states with a powerful – but flexible – tool to apply the most cost- effective emission reduction strategies. The CMAQ language does not mandate emission reductions but instead offers states the ability to evaluate their own needs and seek a range of solutions, including using CMAQ funds for diesel retrofits.


Legislative Information:
US Code § 149. Congestion mitigation and air quality improvement program
Library of Congress information on PL 109-59
CMAQ section of PL 109-59

Additional legislative information can be found at The Library of Congress THOMAS site.

Background Information and Reports:
The CMAQ Solution to Diesel Emissions: How to Use CMAQ More Effectively
Transportation Research Board “The CMAQ Program: Assessing 10 Years of Experience” (Please note, this link takes you to the National Academies Press so that you may purchase the report).
A Methodology for Comparing the Cost-Effectiveness of CMAQ Projects (Wescott Study commissioned by ECTA)

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Photograph: Provided courtesy of Johnson Matthey.