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Official Release of EMFAC2000 Motor Vehicle Emission Factor Model for Use in the San Francisco Bay Area; State of California

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Environmental Protection Agency (EPA).


Notice of availability.


EPA is approving and announcing the availability of the latest version of the California EMFAC model for use in ozone State Implementation Plan (SIP) development in the San Francisco Bay Area. EPA is approving the model for use in the Bay Area with certain conditions due to technical limitations of the model. The model is only approved for use in development of ozone motor vehicle emission factors for SIP development and future conformity determinations in the San Francisco Bay Area.


This determination is effective Jnauary 11, 2002.

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Karina O'Connor (775) 687-4670, x3112, Air Planning Office (AIR-2), Air Division, U.S. EPA Region 9, 75 Hawthorne Street, San Francisco, California.

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I. Background

A. What Is the EMFAC Model?

The EMFAC model is part of the California Air Resources Board's (CARB's) Motor Vehicle Emission Inventory (MVEI) modeling system. The first three models in the system are the CALIMFAC, the WEIGHT and the EMFAC models. The CALIMFAC model estimates emission rates for California on-road vehicles when the vehicle is new and as it ages. The WEIGHT model determines each vehicle model year's accumulated mileage and the relative weight each vehicle model year should be given in the California statewide emission inventory. The EMFAC model combines the results from these two models, along with correction factors and other data, to produce emission factors for the entire California vehicle fleet.

B. Why Are We Announcing Our Approval of the EMFAC Model?

Clean Air Act section 172(c)(3) and 40 CFR 51.112(a)(1) require that SIP inventories be based on the most current and applicable emission estimation models that are available at the time the SIP is developed. Clean Air Act section 176(c)(1) requires that the latest emission estimates be used in transportation conformity analyses. Transportation conformity is a Clean Air Act requirement to ensure that federally supported highway and transit activities are consistent with (“conform to”) the SIP. Conformity to a SIP means that a transportation activity will not cause or contribute to new violations of ambient air quality standards; worsen existing violations; or delay timely attainment of such standards.

Under 40 CFR 93.111(a), EPA must approve new versions of EMFAC for SIP development before they can be used in conformity analyses. In its November 30, 2001 letter, CARB requested that EPA approve EMFAC2000 for use in Bay Area ozone SIP development and transportation conformity determinations. EPA notes that EMFAC2000 would normally be considered the latest emissions model for statewide use in California SIP development (rather than an interim update to the EMFAC model as EMFAC7G was an interim update to EMFAC7F). EMFAC2000 is a significant change from previous EMFAC models and is capable of calculating motor vehicle emissions for all California areas. However, EMFAC2000 is now known to contain technical limitations. It would be inappropriate to approve EMFAC statewide for all SIPs and conformity determinations.

C. Why Is EPA Approving This Version of EMFAC for Only Ozone Emission Analyses in the Bay Area?

EPA is approving EMFAC2000 for ozone SIP development for only the Bay Area at this time. EPA is proceeding with this approval because: (1) EMFAC2000 is an improvement on existing available models despite certain technical limitations; and (2) CARB has committed to revise the Bay Area ozone attainment SIP's motor vehicle emissions budgets with EMFAC2001 or a successor model as part of its mid-course review SIP revision in April 2004. Additionally, we understand that the next EMFAC model will correct EMFAC2000's technical limitations and be available for use in all future California SIPs. Therefore, CARB does not currently intend to develop other SIPs with EMFAC2000.

II. EPA Action

A. What Version of EMFAC Is EPA Approving?

In this notice, EPA is approving and announcing that EMFAC 2000, as developed by CARB and submitted for approval to EPA on November 30, 2001, Start Printed Page 1465is available to use in the development of ozone motor vehicle emission estimates in the Bay Area, as described above. Note that CARB refers to EMFAC in its request for approval as the SF Bay Area-EMFAC 2000.

B. When Will the Technical Limitations in EMFAC 2000 Be Corrected?

CARB will fix the technical errors in EMFAC 2000 in its next version of EMFAC. At this time EPA understands that EMFAC2001 or its successor will be released by CARB before any additional California SIPs are submitted to EPA. EMFAC2001 or its successor will also include a user interface so local agencies can examine alternative scenarios and update local data (e.g., vehicle miles traveled (VMT), fleet characteristics). The future model will allow transportation agencies to complete their own conformity determinations. Note that the Bay Area SIP includes CARB's commitment to revise the SIP with the latest technical information as part of its mid-course review in April 2004, which was subject to the state public comment process. EPA understands that California will not be submitting EMFAC2001 or its successor for EPA approval until early 2003, so that CARB's submission of the mid-course review using the newly available model will occur within one year of EPA's approval of EMFAC2001 or its successor. This is consistent with EPA's past practice where older versions of models such as the national MOBILE model have been used prior to release of newer versions of the model that make certain corrections in emission estimation.

C. What Pollutants Can EMFAC2000 Be Used To Estimate?

EPA is approving the model only for use to estimate ozone emissions. Since this approval is specific to ozone for the Bay Area, carbon monoxide microscale analyses in the Bay Area should continue to be based on EMFAC7F.

D. Will a Conformity Grace Period for the Entire State of California Be Started by This Approval of EMFAC2000?

No. The transportation conformity rule (40 CFR part 93.111) requires that conformity analyses be based on the latest motor vehicle emissions model approved by EPA for SIP purposes for a state or area. When EPA approves a new emissions model like EMFAC2000, we normally establish a grace period before the model is required for new conformity analyses (40 CFR 93.111(b)). However, as explained above, EMFAC2000 is known to contain a few technical problems. Due to the limitations of EMFAC2000, it would be inappropriate to approve EMFAC2000 statewide for all SIP planning, and thus to require its use for conformity determinations in all areas, particularly those without a SIP and budgets based on EMFAC2000. Based on discussions with CARB, EPA understands that EMFAC2001 or its successor will correct the limitations and include additional improvements. Therefore, EPA is not approving EMFAC2000 for statewide SIP planning, and a conformity grace period for the entire state will not be established for EMFAC2000.

Although EPA's potential approval of EMFAC2001 or its successor will not occur until farther into the future, EPA currently intends to establish a grace period before EMFAC2001 or its successor would be required for new transportation conformity analyses across the state of California. From now until the end of such a grace period, nonattainment and maintenance areas outside the Bay Area can continue to use EMFAC7F and EMFAC7G as appropriate for new conformity analyses. For more information about the use of EMFAC7F and EMFAC7G, please see the April 16, 1998, EPA Region IX letter to CARB describing the applicability of these models for conformity analyses.

EMFAC2000 will apply for all future ozone conformity analyses in the Bay Area until one of the following two scenarios occurs (1) a revised attainment SIP and budgets with EMFAC2001 or its successor are submitted and EPA has found these revised budgets adequate or (2) the grace period for EMFAC2001 or its successor has expired. Since EPA is approving EMFAC2000 for use in the Bay Area based on CARB's commitment to revise the Bay Area ozone SIP once an improved model is available, EPA intends to approve the motor vehicle emission budgets in any Bay Area ozone SIP only until new budgets developed with the new model are submitted and found adequate for conformity purposes.

E. Will any Special Requirements Apply to Bay Area Conformity Analyses Using EMFAC2000?

Since EMFAC2000 contains VMT estimates developed by CARB, CARB has committed in its November 30, 2001 letter requesting approval of EMFAC2000, to work with the Metropolitan Transportation Commission (MTC) to complete future conformity analyses in the Bay Area. Once EMFAC2001 or its successor is approved generally for use in California, MTC, like other MPOs, should be able to use the EMFAC model to examine alternative scenarios with its own VMT estimates for future conformity analyses.

III. Summary of EPA Actions

EPA is approving EMFAC2000 as submitted by CARB on November 30, 2001 with the following limitations and conditions.

(1) The approval is limited to the Bay Area.

(2) The approval is limited to ozone.

(3) No statewide conformity grace period will be triggered.

(4) CARB will correct the technical limitations in EMFAC2001 or its successor, and EPA understands that the new model will be released by CARB for EPA approval before any additional California SIPs are submitted to EPA.

(5) CARB will revise the Bay Area ozone SIP with EMFAC2001 or its successor in its mid-course review of the Bay Area SIP by April 2004.

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Dated: January 4, 2002.

Wayne Nastri,

Regional Administrator, Region IX.

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[FR Doc. 02-756 Filed 1-10-02; 8:45 am]