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Clean Air Construction Overview and Requirements

The Clean Air Construction (CAC) Program is a collaboration among public agencies in the Portland Metro Area to reduce diesel emissions on their construction projects. 
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The Clean Air Construction (CAC) Program is a collaboration among the City of Portland, Port of Portland, Multnomah County, Washington County, TriMet, Portland Community College and Metro ("CAC Agencies") to reduce diesel emissions on our agency's construction projects.  We aim to accomplish this by:

  • implementing a standard set of idle reduction and diesel equipment requirements on job sites and
  • implementing a regional program to verify compliance with the requirements.  

By adopting the same approach and working together, we will minimize related administrative burdens on contractors and CAC Agencies.

Clean Air Construction - Agency Contract Dollar Thresholds 

The Clean Air Construction Requirements are consistent across participating CAC Agencies, however each agency applies the requirements at different contract thresholds.  Below is a list of the contract thresholds each agency has adopted (as of 7/30/2020).

  • City of Portland - all construction contracts over $1,000,000
  • Multnomah County -  all construction contracts over $500,000
  • Metro - all construction contracts over $500,000
  • Portland Community College - all construction contracts over $1,000,000
  • Port of Portland - all construction contracts over $2,000,000
  • TriMet - all public improvement contracts
  • Washington County - all construction contracts over $500,000

Idle Reduction Requirements

Beginning January 1, 2020 contractors working on CAC Agencies construction projects shall take the following steps to reduce unnecessary diesel equipment idling:

  • All nonroad diesel equipment must shut down after five (5) minutes of inactivity, and
  • All nonroad diesel equipment shall have decals/prompts visible to the operator to remind them to shut down the equipment after five (5) minutes of inactivity, and
  • Contractors will post “Five Minute Limit” signs in high foot traffic areas of the job site, visible to workers, and
  • Contractors will ensure all diesel equipment operators are aware of the policy.

>>Example 5-Minute Idling Limit Sign/Prompt

Exemptions to the above idle reduction requirements are allowed in circumstances where:

  • the safety of contractors and their employees may be compromised if diesel equipment is turned off; for example, where employees are working in a trench; or
  • the equipment meets the most stringent EPA emissions standards or has been retrofit with a DPF; or
  • frequent shutdowns may be detrimental to the exhaust control system, reducing the effectiveness of that system by lowering the exhaust temperature; or
  • equipment requires testing, servicing, inspection, or repairs.

Diesel Engine Requirements and Phase-In Schedule - UPDATED September 2020

Effective January 1, 2022 and in accordance with the phase-in schedule outlined below all diesel-powered nonroad construction equipment greater than 25 horsepower and all on-road diesel dump trucks and concrete mixers used on CAC Agency construction projects must meet the following CAC Engine Requirements.  When pursuing diesel emission control device retrofits, equipment and vehicle owners shall install the emission control device that maximizes diesel particulate matter reductions for that specific piece of equipment or vehicle in accordance with the Compliance Options Protocols.

Table of the Clean Air Construction Requirements and Timeline


Contractors may apply for exemptions to the above diesel engine requirements on a per project basis in circumstances where:

  • The equipment/vehicle is required for an emergency (including for underground equipment operators).
  • After following the Compliance Options Protocol, the required emission control device would obscure operator lines of sight or otherwise impact worker safety or the equipment is not able to be retrofit with a verified emission control device; and no compliant rental equipment is available within 100 miles of the job site.
  • After following the Compliance Options Protocol, the contractor can demonstrate that due to the uniqueness of the equipment/vehicle or similar special circumstances, it is not reasonable to comply with the diesel engine requirement for a specific piece of equipment/vehicle.

Compliance Options Protocols

The Compliance Options Protocols guide equipment owners through which compliance option applies to their equipment following a "Best Available Technology" approach.  In other words, the compliance option for a specific piece of equipment must be the option that reduces the diesel particulate matter the most within the capabilities of that piece of equipment.  Compliance with the CAC Diesel Engine Requirements will be determined according to the following protocols.

Table of the Clean Air Construction Nonroad Compliance Options Protocol
Chart of compliance protocol steps for on-road engines

Compliance and Verification

Contractors (prime and sub-contractors, and applicable suppliers) will demonstrate compliance with the Clean Air Construction requirements on an annual basis by providing to the applicable contracting agency, or approved program operator, all requested diesel equipment/vehicle information needed to verify compliance, including confirmation that retrofit devices are maintained on the equipment in proper operating condition. Upon determining compliance with the requirements, the applicable contracting agency, or approved program operator, will issue an equipment/vehicle decal for each compliant piece of equipment/vehicle. This decal must be displayed on the compliant equipment/vehicle at all times in a location readily visible to agency staff. In addition, random on-site inspections by agency staff (or approved program operator) will be conducted on a project by project basis.  Additional details regarding consequences for noncompliance will be determined on an agency-by-agency basis.  Additional implementation/program elements are currently in development. 

Clean Air Construction Definitions

CARB: California Air Resources Board, a state regulatory agency charged with regulating the air quality in California.

Diesel Particulate Matter: the solid or liquid particles found in the air released through the exhaust from diesel vehicles/equipment. Exposure to diesel particulate matter increases the risk of heart attack, stroke, cardiovascular disease, exacerbates asthma, and can lead to low-weight and pre-term births. Diesel particulate matter is also a known as a human carcinogen as determined by the International Agency for Research on Cancer.

DMWESB: Disadvantaged, Minority, Women, or Emerging Small Business as certified by the State of Oregon Certification Office for Business Inclusion and Diversity

DOC: Diesel oxidation catalyst. A device designed to reduce harmful diesel emissions such as carbon monoxide, hydrocarbons and certain diesel particulate emissions.

DPF: Diesel particulate filter. A device designed to trap all diesel particulate matter above a certain size.

Emission Control Device: technology added to equipment to reduce harmful emissions. These may include catalytic converters and particulate filters, among other technologies. 

EPA: U.S. Environmental Protection Agency, a federal regulatory agency charged with regulating the environment.

Nonroad: Construction equipment and vehicles that fall under the EPA non-road engine equipment category, which includes all diesel equipment not intended for highway use. For the purpose of this policy, these vehicles/equipment include only diesel construction vehicles/equipment with engines larger than 25 horsepower, which includes tractors, excavators, dozers, scrapers and other construction vehicles/equipment.

SDVB: Service Disabled Veteran Business as certified by the State of Oregon Certification Office for Business Inclusion and Diversity.