Search Air Quality Web Site
CLEAN AIR MAKE MORE

Diesel Idling

P-21 Vehicle Idling Restriction Ordinance

Reducing emissions from diesel engines is one of the most important air quality challenges facing the country. Even with EPA’s more stringent heavy-duty highway and non-road engine standards set to take effect over the next decade, millions of diesel engines already in use will continue to emit large amounts of nitrogen oxides, particulate matter and air toxics, which contribute to serious public health problems. The Maricopa County Air Quality Department is dedicated to achieving emission reductions from diesel sources.


  1. P-21 Maricopa County Vehicle Idling Restriction Ordinance
    On June 26, 2002, Maricopa County adopted an ordinance restricting idling of heavy-duty diesel vehicles. The purpose of this ordinance is to protect public health and the environment by reducing emissions of toxics and criteria pollutants while also conserving fuel. These vehicles are required to limit idling to no longer than five minutes under most circumstances. View the Maricopa County Vehicle Idling Restriction Ordinance.
  2. Who is affected by the Maricopa County Ordinance?
    Operators of a diesel-fueled commercial motor vehicle that weighs more than 14,000 pounds operating in Maricopa County, regardless of where the vehicle is registered. It applies to vehicles designed to operate on public highways and powered by a diesel engine.
  3. What are the penalties for non-compliance of the County Ordinance?
    The driver of the vehicle who violates this ordinance is subject to a minimum civil penalty of $100 for the first violation and $300 for a second or any subsequent violation.
  4. Where does this Ordinance Apply?
    The Maricopa County Vehicle Idling Restriction Ordinance applies to vehicles idling within Maricopa County.
  5. Are there exceptions
    • Drivers stuck in traffic due to congestion or weather issues.
    • The main engine is being idled during DOT mandated rest periods (US 49 CFR Part 395, AZ R17-5-202).
    • The main engine is being idled in order to conform to the manufacturer's "warm up" or "cool down" specifications.
    • The main engine is being idled for maintenance or diagnostic purposes.
    • The main engine meets ALL of the following:
      • Provides a necessary power source for mechanical operations other than propulsion
      • Involves a Power-Take-Off (PTO) mechanism
      • Powers the loading/unloading of cargo, the mixing or processing of cargo, the temperature control of cargo, or a mechanical extension to perform work functions
    • Passenger buses (including school buses), which are being idled in order to provide heat or air conditioning necessary for comfort/safety may idle for up to:
      • 30 minutes during any 60 minute period
      • When temperatures exceed 75 degrees Fahrenheit, allowed to idle up to 60 minutes during any 90 minute period
      • Emergency and/or law enforcement purposes
  6. What Can I Do About Idling Emissions?
    File a Complaint
    You may use any of the following options to report a suspected idling violation: