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Durability Compliance Program

The goal of the Durability Compliance Program is to ensure that manufacturer durability programs accurately predict in-use emission levels and deterioration rates for vehicles they wish to certify. The predictions must reflect in-use vehicle field data and engineering knowledge of the emission control system. The following information is designed to assist manufacturers as they demonstrate compliance with emission standards for the intermediate and full useful life of a vehicle.

Manufacturers may use accelerated deterioration methods and artificial aging techniques to simulate wear on vehicle and emission system components. Manufacturers may also use proprietary aging cycles to conduct their durability program. All manufacturer durability program plans must be submitted to EPA annually for review and approval. In addition, manufacturers that use a unique aging cycle for durability demonstration purposes must develop an equivalency factor (read Equivalency Factors below for more details) that equates their cycle to a standard EPA aging cycle. Specifically, the equivalency factor relates the amount of aging performed on the unique road or bench aging cycle to the amount of aging that occurs over EPA's standard cycles.

EPA will provide a list of manufacturer equivalency factors and other applicable vehicle information for each model year on this web site.

For durability compliance questions please contact: Joel Ball at 734-214-238 (ball.joel@epa.gov).

NOTE: You will need Adobe Acrobat Reader, available as a free download, to view some of the files on this page. See EPA's PDF page to learn more about PDF, and for a link to the free Acrobat Reader.


Final Rule and Supplemental Notice for Durability Procedures for New Light-Duty Vehicles, Light-Duty Trucks, and Heavy-Duty Vehicles (Published January 17, 2006)



Manufacturer Guidance on Compliance Demonstration with the Emissions Durability Procedures and Regulations (PDF) (5 pp, 49K, April 2007)

Equivalency Factors

The purpose of equivalency factors is stated in the preamble language contained in the January 17, 2006, 71 FR 2818, Final Rule (PDF) (33 pp, 361K, published January 17, 2006)

Manufacturers have three options to demonstrate full useful life durability (120,000 or 150,000 miles) of their vehicles and emission control components:

  • EPA Standard Road Cycle or Standard Bench Cycle (SRC/SBC): EPA developed the Standard Road Cycle (EPA SRC: 40 CFR Part 86, Appendix V) and the Standard Bench Cycle (EPA SBC: 40 CFR Part 86, Appendix VII and Appendix VIII) to provide a universal road/bench aging cycle. These cycles are available to all manufacturers for purposes of demonstrating durability. Manufacturers may use a standard EPA cycle without prior EPA approval but must inform EPA of their intent to do so when they submit their durability plan for review.

    In addition, EPA has developed a "Bench Aging Time" (BAT) calculator that outputs the bench aging hours and temperature necessary on the SBC to replicate aging and deterioration that would occur on a road cycle (either the SRC or a manufacturer's alternative cycle).

  • Alternative Road or Bench Cycles (ARC/ABC): Manufacturers may design their own cycles to mimic the aging or deterioration of emission control components that would occur on real-world vehicles over their useful life. These cycles are typically designed to reproduce useful life aging/deterioration in a shorter period of time.  The manufacturer can choose to age the emission control components on the vehicle (i.e., whole vehicle aging) or, to reduce cost and test burden, use a test bench to age the emission control components (i.e., bench aging).  Manufacturers must obtain prior EPA approval to use an alternative road or bench cycle.
  • Customized Standard Road Cycle or Standard Bench Cycle (Cust. SRC/SBC): Manufacturers may also customize the EPA SRC/SBC to fit their specific in-use vehicle fleet aging/deterioration rates (e.g., higher speeds regimes to achieve more deterioration within the full useful life) or unique test facilities such as changing EPA SRC lap length to accommodate the length of their service accumulation track. These methods also require prior EPA approval.

The standard EPA bench and road cycles represent a baseline or measuring stick for all other cycles since they can be applied to all vehicles.  Manufacturer-derived alternative or customized cycles may be more or less severe than the SRC/SBC, depending on the design of the cycle.  Therefore, EPA requires manufacturers to develop an equivalency factor, or EF, that can be used for comparison.  Specifically, the EF is the ratio of the SBC bench aging hours for a manufacturer-derived alternative or customized cycle and the SBC bench aging hours for the SRC, at the applicable full useful life mileage.

Specific details on how to calculate and use the EF are provided in Manufacturer Guidance on Compliance Demonstration with the Emissions Durability Procedures and Regulations (PDF) (5 pp, 49K, April 2007). Note that manufacturers using the EPA SRC and/or SBC for durability demonstration will simply have an equivalency factor of 1.0.

The equivalency factors must be provided by manufacturers of light-duty vehicle, light-duty trucks and heavy-duty vehicles each model year and will be published semi-annually on this site.

Durability Program Equivalency Factors

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Bench Aging Time Calculator

The Bench Aging Time (BAT) calculator is used to determine the appropriate aging temperature and time on the EPA’s Standard Bench Cycle (SBC) that will replicate aging performed using a road cycle. The BAT calculator requires a catalyst temperature profile generated from an actual vehicle to calculate the aging temperature and time. See below for further discussion on how to create the catalyst temperature profile and how it is used in the BAT calculator.

Bench Aging Time (BAT) Calculator

How is the temperature profile created and how is it used in the BAT calculator?

The catalyst temperature profile can be created by driving an actual vehicle over a prescribed road cycle (either EPA’s SRC or an alternative cycle) and collecting catalyst temperature information. Thermocouples are inserted in the hottest portion of the catalyst and the temperature is recorded at some frequency over the road cycle to create the temperature profile (e.g.. data set or a plot of temperature versus time). The temperature profile is input into the BAT calculator to determine a single, composite temperature (reference temperature) and amount of time at that reference temperature (time-at-temperature) that represents the range of temperatures in the temperature profile. Using this reference temperature and time-at-temperature, an exhaust system with the catalyst and oxygen sensors, is placed down stream from an engine, or other source that can produce/simulate exhaust gases, and operated in a mode that produces the reference temperature for the determined amount of time. As a result, a bench aging system and the BAT values can be used to achieve equivalent aging to a road cycle. Please refer to the Durability Regulations for specifics on data recording frequency and processing methods for catalyst temperature profiles.

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