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San Joaquin Valley

Federal Ozone Nonattainment Area

April 24, 2014
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INTRODUCTION

The purpose of the vehicle miles travelled (VMT) emissions offset demonstration for the 

1-hour and 8-hour ozone standards is to respond to U.S. EPA’s action withdrawing 

approval of revisions to California’s State Implementation Plan for the San Joaquin 

Valley published on November 26, 2012 (77 Fed.Reg. 70376). In that action, U.S. EPA 

withdrew its approval of the 2004 1-hour ozone plan (including the VMT emissions 

offset demonstration), and withdrew its approval of the VMT offset demonstration

contained in the 2007 8-hour ozone plan. U.S. EPA’s action is in response to decisions

of the Ninth Circuit Court of Appeals in Association of Irritated Residents v U.S. EPA, 

(9th Cir., reprinted as amended on January 27, 2012, 686 F. 3d 668), and Sierra Club v 

U.S. EPA, (671 F.3d 955 (9th Cir. 2012)).

BACKGROUND

In 1979, U.S. EPA established a primary health-based national ambient air quality 

standard (NAAQS) for ozone at 0.12 parts per million (ppm) averaged over a 1-hour 

period. See 44 Fed.Reg. 8220 (February 9, 1979). The Clean Air Act (CAA), as 

amended in 1990, classified areas that had not yet attained that standard, based on the 

severity of their ozone problem, ranging from Marginal to Extreme. Extreme areas were 

provided the most time to attain, until November 15, 2010, but were also subject to the 

most stringent requirements. In particular, Severe and Extreme areas were subject to 

CAA Section 182(d)(1)(A), which requires state implementation plans to adopt “specific 

enforceable transportation control strategies and transportation control measures to 

offset any growth in vehicle miles traveled or numbers of vehicle trips in such area....” 

U.S. EPA designated the San Joaquin Valley Air Basin as “Extreme” on April 16, 2004

(69 Fed Reg 20550). Thus the San Joaquin Valley Air Basin was subject to this 

requirement. The U.S. EPA has historically interpreted this provision of the CAA (now 

called “VMT emissions offset requirement”) to allow areas to meet the requirement by 

demonstrating that emissions from motor vehicles decline each year through the 

attainment year. See, e.g., 57 Fed. Reg. 13498, at 13521-13523 (April 16, 1992).

NEW OZONE STANDARD

In 1997, U.S. EPA replaced the 1-hour ozone standard with an 8-hour standard of 0.08 

ppm [62 Fed.Reg. 38856 (July 18, 1997)]. The U.S. EPA promulgated rules 

implementing the new standard. The “Phase 1” rule was issued on April 30, 2004 (69 

Fed.Reg. 23951). That rule includes anti-backsliding requirements that meant that 

many requirements remained applicable even after the revocation of the 1-hour 

standard, which was effective June 2005. See 40 CFR §51.905(a)(1) and §51.900(f). 

In particular, an area that was classified as Extreme for the 1-hour standard would 

remain subject to the VMT emissions offset requirement even if it would not otherwise 

have been subject to that requirement based on its classification under the new 8-hour 

ozone standard [40 CFR §51.900(f)(11)]. The U.S. EPA’s Phase 2 rule, issued on 
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November 29, 2005 (70 Fed. Reg. 71612) required that areas classified as Severe or 

Extreme under the new 8-hour standard would also be subject to the VMT offset 

requirement.

SAN JOAQUIN VALLEY SIP SUBMISSIONS FOR VMT OFFSET 

REQUIREMENT AND LITAGATION

U.S. EPA approved the 2004 Extreme Ozone Attainment Demonstration Plan (2004 1-

Hour Ozone Plan) and the 2007 Ozone Plan (for the 1997 8-hour ozone NAAQS) on 

March 8, 2010 and March 1, 2012, respectively. Each plan contained VMT emissions 

offset demonstrations consistent with EPA’s interpretation of CAA §182(d)(1)(A) at the 

time of submission and approval. 

Subsequent to those approvals, a decision of the Ninth Circuit Court of Appeals in 

Association of Irritated Residents (AIR) v U.S. EPA (reprinted as amended on January 

27, 2012, 632 F.3d 584, 9th Cir. 2011) rejected EPA’s interpretation of the CAA, which 

had provided the basis for U.S. EPA’s approval of VMT offset demonstrations in district 

plans. With the AIR decision, the Court determined that the CAA requires additional 

transportation control strategies and measures whenever vehicle emissions are 

projected to be higher than would have been had VMT not grown, even if aggregate 

vehicle emissions are decreasing. 

In addition to the Court’s ruling in the AIR case, a previous Ninth Circuit Court of 

Appeals decision (Sierra Club v EPA, 671 F.3d 955 (9th Cir. 2012)) found that U.S. 

EPA’s action approving the 2004 1-Hour Ozone Plan was arbitrary and capricious under 

the Administrative Procedure Act because it did not take into account new emissions 

inventory data that California had submitted subsequent to submittal of the plan. The 

Court remanded U.S. EPA’s approval back to the agency in its entirety. 

On November 26, 2012, in an effort to address issues pertinent to both court cases, 

U.S. EPA withdrew its March 8, 2010 final action approving state implementation plan 

(SIP) revisions submitted by the California Air Resources Board (ARB) to provide for 

attainment of the 1-hour ozone NAAQS in the San Joaquin Valley extreme ozone 

nonattainment area (77 Fed. Reg. 70376). In the same March 8, 2010 final action, EPA 

also withdrew the March 1, 2012 approval of the VMT Offset Demonstration in the 2007 

8-hour Ozone Plan. 

U.S. EPA GUIDANCE ON VMT OFFSET REQUIREMENT

In August 2012, U.S. EPA issued guidance entitled “Implementing Clean Air Act Section 

182(d)(1)(A): Transportation Control Measures and Transportation Control Strategies to 

Offset Growth in Emissions Due to Growth in Vehicle Miles Travelled”. Among other 

things, U.S. EPA’s guidance points out that the Court, in the AIR decision, omitted any 

reference to “transportation control strategies” (TCS). TCSs, which are not defined in 
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the CAA or U.S. EPA regulation, are eligible to offset growth in emissions due to growth 

in VMT. The U.S. EPA’s new guidance indicates that technology improvements such as 

vehicle technology improvements, motor vehicle fuels, and other control strategies that 

are transportation-related could be used to offset increases in emissions due to VMT. 

U.S. EPA’s revised guidance sets forth a method of calculating the actual growth in 

emissions due to growth in VMT. Essentially, the state would compare projected 

attainment year emissions assuming no new control measures and no VMT growth with 

projected actual attainment year emissions (including new control measures and VMT 

growth). If the latter number is smaller than the former, no additional transportation 

control measures or strategies would be required. If additional transportation control 

measures and transportation control strategies are required, they should be clearly 

identified and distinguished from the measures included in the initial calculations for the 

base year and the three scenarios identified for the attainment year.

In addition, the guidance recommends that the base year to be used in the 

demonstration be the base year used in the attainment demonstration for the ozone 

ambient air quality standard. This Appendix includes VMT offset demonstrations in 

accordance with U.S. EPA’s new guidance for both the 8-hour and 1-hour ozone 

requirements. To address U.S. EPA’s guidance on the base year, two base years are 

used: 2002 for the 1997 8-hour standard and 1990 for the 1-hour ozone standard.

TRANSPORTATION CONTROL STRATEGIES AND TRANSPORTATION 

CONTROL MEASURES

By listing them separately, the Clean Air Act [CAA §182(d)(1)(A)] differentiates between 

transportation control strategies (TCS) and transportation control measures (TCM), and 

thus provides for a wide range of strategies and measures as options to offset growth in 

emissions from vehicle miles traveled (VMT) growth. In addition, the example TCMs 

listed in Section 108(f)(1)(A) of the CAA include measures that reduce emissions by 

reducing VMT, reducing tailpipe emissions, and removing dirtier vehicles from the fleet. 

California’s motor vehicle control program includes a variety of strategies and measures 

including new engine standards and in-use programs (e.g., smog check, vehicle scrap, 

fleet rules, idling restrictions). TCMs developed by the eight San Joaquin Valley 

Metropolitan Planning Organizations (MPOs) provide additional reductions. In addition, 

the eight MPOs report every two years on the implementation status of TCMs in their 

jurisdiction.

Based on the provisions in Section 182(d)(1)(A) and the clarifications provided in the 

U.S. EPA guidance, any combination of transportation control strategies and TCMs may 

be used to meet the requirement to offset growth in emissions resulting from VMT 

growth. Since 1990 when this requirement was established, California has adopted 

more than sufficient enforceable transportation strategies and measures to meet the 

requirement to offset the growth in emissions from VMT growth. For the 1997 8-hour 

standard offset demonstration, 2002 controls are used as the base case control level 

since 2002 is the base year of the SIP. For the 1-hour ozone standard demonstration, 
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1990 level controls are used as the base year control level since 1990 is the base year 

for the 1-hour SIP. 

A list of the state’s mobile source control program adopted since 1990 is provided in 

Attachment 1. In addition, a list of TCMs implemented in the San Joaquin Valley Air 

Basin is provided in Attachment 2.

EMISSIONS DUE TO VMT GROWTH

As discussed above, the U.S. EPA guidance does provide a recommended calculation 

methodology that could be done to determine if sufficient transportation control 

strategies and TCMs have been adopted and implemented to offset the growth in 

emissions due solely to growth in VMT. As such, any increase in emissions solely from 

VMT increases in the future attainment year from the base year (assuming that there 

are no further motor vehicle control programs implemented after the base year) would 

need to be offset. In addition, a calculation is needed to show the emissions levels if 

VMT had remained constant from the base year to the future attainment year. As 

discussed earlier, a comparison of the projected attainment year emissions assuming 

no new control measures and no VMT growth with projected actual attainment year 

emissions (including new control measures and VMT growth) would be made. If the 

latter number is smaller than the former, no additional transportation control measures 

or strategies would be required.

METHODOLOGY

The following calculations are based on the U.S. EPA guidance recommended 

calculation methodology. As shown for the 8-hour ozone standard, 2002 is the base 

year used for the attainment demonstration and 2023 is the attainment year. For the 1-

hour ozone standard demonstration, 1990 serves as the base year and 2017 is the 

projected attainment year. 

Analysis Tool

This analysis uses California’s approved motor vehicle emissions model, EMFAC. 

The EMFAC model estimates the emissions from two combustion processes: running 

exhaust and start exhaust, and four evaporative processes: hot soak, running losses, 

diurnal, and resting losses.

Emissions from running exhaust, start exhaust, hot soak, and running losses are a 

function of how much a vehicle is driven. Emissions from these processes are directly 

related to VMT, trips, and starts. These processes are included in the calculation of the 

emissions levels used in the VMT offset demonstration. Emissions from resting loss 

and diurnal loss processes are not related to VMT, trips or vehicle starts and are not 
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included in the analysis because these emissions occur regardless if the vehicle makes 

a trip (i.e. a start) or not.

EMFAC combines trip-based VMT from the regional transportation planning agencies, 

starts data based on household travel surveys, and vehicle population data from the 

Department of Motor Vehicles with corresponding emission rates to calculate 

emissions. 1

With the EMFAC model, the calculation of emissions growth and whether it is offset is 

simplified to a comparison of future year emissions with “no growth” in VMT or new 

control strategies to future emissions with VMT growth and new control strategies. This 

follows EPA’s 2012 guidance and is consistent with the Ninth Circuit’s interpretation of 

CAA section 182(d)(1)(A).

The Advanced Clean Cars (ACC) regulations adopted by ARB in 2012 are not included 

in EMFAC 2011. The output from EMFAC 2011 was adjusted off-model to estimate the 

benefits of the ACC regulations. No other off-model adjustments were taken. 

Analysis Using 2002 as the Base Year for the 1997 8-hour Ozone Standard with 

Attainment Year of 2023.

Step 1. Provide the emissions level for the base year.

The following table shows the VOC emissions, VMT, starts, and vehicle population for 

calendar year 2002 from the EMFAC2011 model.

Summary of 2002 Base Year

VMT

(thousand miles/day)

Starts 

(thousands/day)

Vehicle 

Population

(thousands)

VOC 

Emissions

(tons/day)

2002 Base Year 78,400 11,307 1,826 76

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1 More information on data sources can be found in the EMFAC technical document which is located on 

the web at: http://www.arb.ca.gov/msei/emfac2011-technical-documentation-final-updated-0712-v03.pdf
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Step 2. Calculate three emissions levels in the attainment year.

For the attainment year,

(1) Calculate emissions level with the motor vehicle control program frozen at 

2002 levels and with projected VMT, starts, and vehicle population for the 

attainment year. This represents what the emissions in the attainment 

year would have been if transportation control strategies and TCMs had 

not been implemented after 2002;

(2) Calculate emissions level with the motor vehicle control program frozen at 

2002 levels and assuming VMT, starts, and vehicle population do not 

increase from 2002 levels; and

(3) Calculate an emissions level that represents emissions with full 

implementation of all transportation control strategies and TCMs since 

2002 and which represents the projected future year baseline emissions 

inventory using the VMT, starts, and vehicle population for the attainment 

year.

Calculation 1. Calculate the emissions in the attainment year 

assuming no new measures since the base year, and including 

growth in VMT, starts, and vehicle population.

To perform this calculation, the California Air Resources Board (CARB) staff 

identified the on-road motor vehicle control programs adopted since 2002 and 

adjusted the EMFAC2011 to reflect the VOC emissions levels in 2023 without the 

benefits of the post-2002 control programs. The projected VOC emissions are 

49 tons/day.

Calculation 2. Calculate the emissions with no growth in VMT, starts, 

or vehicle population.

EMFAC2011 allows the user to input different VMT, starts, and vehicle population 

than default. As such, for this calculation, the EMFAC 2011 model was run 

without the benefit of the post 2002 control program for calendar year 2023 with 

the 2002 level of VMT of 78,399,543 miles per day, the 2002 level of starts at 

11,307,036 per day, and the 2002 level of population at 1,825,573 vehicles. The 

VOC emissions associated with 2002 VMT, starts, and vehicle population are 

28 tons/day.
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Calculation 3. Calculate emission reductions with full 

Implementation of Transportation Control Strategies & TCMs.

The VOC emission levels for 2023 assuming the benefits of the post-2002 motor 

vehicle control program and the projected VMT, starts, and vehicle population in 

2023 are calculated using EMFAC2011. The projected VOC emissions level is 

24 tons/day. VOC emissions for the three sets of calculations described above 

are provided in the following table.

Summary of 2023 Attainment Year Emissions Levels

* CY 2023 VMT based on 2013 FTIPs from the 8 San Joaquin Valley MPOs

** Does not include diurnal or resting loss emissions.

Description

VMT* 

(miles/day, 

thousands)

Starts

(thousands/day)

Vehicle 

Population

(thousands)

VOC 

Emissions** 

(tons/day)

(1)

Emissions with 

Motor Vehicle 

Control Program 

Frozen at 2002 

Levels. 

(VMT, starts and vehicle 

population at 2023 levels.)

130,431 19,466 3,047 49

(2)

Emissions with 

Motor Vehicle 

Control Program 

Frozen at 2002 

Levels. 

(VMT, starts, and vehicle 

population at 2002 levels)

78,400 11,307 1,826 28

(3)

Emissions with Full 

Motor Vehicle

Control Program in 

Place

(VMT, starts and vehicle 

population at 2023 levels)

130,431 19,466 3,047 24
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As provided in the U.S. EPA guidance, to determine compliance with the provisions of 

Section 182(d)(1)(A) of the federal Clean Air Act, the emissions levels calculated in 

Calculation 3 should be less than the emissions levels in Calculation 2:

VOC: 24 < 28 tons/day

Analysis Using 1990 as the Base Year for the 1-hour Ozone Standard with 

Attainment Year of 2017.

Step 1. Provide the emissions levels for the base year.

The following table shows the VOC emissions, VMT, starts, and vehicle population for 

calendar year 1990 from the EMFAC2011 model.

Summary of 1990 Base Year

VMT

(thousand miles/day)

Starts 

(thousands/ day)

Vehicle 

Population

(thousands)

VOC 

Emissions

(tons/day)

1990 Base Year 52,199 7,730 1,269 196

Step 2. Calculate three emissions levels in the attainment year.

For the attainment year,

(1) Calculate emissions level with the motor vehicle control program frozen at 

1990 levels and with projected VMT, starts, and vehicle population for the 

attainment year. This represents what the emissions in the attainment 

year would have been if transportation control strategies and TCMs had 

not been implemented after 1990;

(2) Calculate emissions level with the motor vehicle control program frozen at 

1990 levels and assuming VMT, starts, and vehicle population do not 

increase from 1990 levels; and 

(3) Calculate an emissions level that represents emissions with full 

implementation of all transportation control strategies and TCMs since 

1990 and which represents the projected future year baseline emissions 

inventory using the VMT, starts, and vehicle population for the attainment 

year.
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Calculation 1. Calculate the emissions in the attainment year 

assuming no new measures since the base year, and including 

growth in VMT, starts, and vehicle population.

To perform this calculation, staff identified the on-road motor vehicle control 

programs adopted since 1990 and adjusted the EMFAC2011 model to reflect the 

VOC emissions levels in 2017 without the benefits of the post-1990 control 

programs. The projected VOC emissions are 178 tons per day.

Calculation 2. Calculate the emissions with no growth in VMT, starts, 

or vehicle population.

EMFAC2011 allows the user to input different VMT, starts, and vehicle population 

than default. As such, for this calculation, the EMFAC 2011 model was run 

without the benefit of the post 1990 control program for calendar year 2017 with 

the 1990 level of VMT of 52,198,974 miles per day, the 1990 level of starts at 

7,729,877 per day, and the 1990 level of population at 1,269,165 vehicles. The 

VOC emissions associated with 1990 VMT, starts, and vehicle population are 

81 tons/day. 

Calculation 3. Calculate emission reductions with full 

implementation of Transportation Control Strategies and TCMs.

The VOC emission levels for 2017 assuming the benefits of the post-1990 motor 

vehicle control program and the projected VMT, starts, and vehicle population in 

2017 are calculated using EMFAC2011. The projected VOC emissions level is 

30 tons/day. VOC emissions for the three sets of calculations described above 

are provided in the following table.
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Summary of 2017 Attainment Year Emissions Levels

* CY 2017 VMT based on 2013 FTIPs from the 8 San Joaquin Valley MPOs

** Does not include resting or diurnal loss emissions.

As provided in the U.S. EPA guidance, to determine compliance with the 

provisions of Section 182(d)(1)(A) of the federal Clean Air Act, the emissions 

levels calculated in Calculation 3 should be less than the emissions levels in 

Calculation 2:

VOC: 30 < 81 tons/day

Description

VMT* 

(miles/day, 

thousands)

Starts

(thousands/ day)

Vehicle 

Population

(thousands)

VOC 

Emissions** 

(tons/day)

(1)

Emissions with 

Motor Vehicle 

Control Program 

Frozen at 1990 

Levels.

(VMT, starts, and vehicle 

population at 2017 levels.)

115,070 17,133 2,688 178

(2)

Emissions with 

Motor Vehicle 

Control Program 

Frozen at 1990 

Levels.

(VMT, starts, and vehicle 

population at 1990 Levels)

52,199 7,730 1,269 81

(3)

Emissions with Full 

Motor Vehicle

Control Program in 

Place

(VMT, starts, and vehicle 

population at 2017 Levels)

115,070 17,133 2,688 30
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SUMMARY

The previous sections provide an analysis to demonstrate compliance with the 

provisions of Section 182(d)(1)(A) of the federal Clean Air Act. To further illustrate the 

demonstration, Figures 1 and 2 below show graphically the emissions benefits of the 

motor vehicle control programs in offsetting VOC emissions due to increased VMT, 

starts, and vehicle population in the San Joaquin Valley Air Basin for both the 1997 8-

hour ozone standard (2002 base year) and the 1-hour ozone standard (1990 base year). 

The left bar (in purple) shows the emissions in the base year with base year controls. 

The three bars on the right in each figure show the emissions levels in the attainment 

year for the three calculations identified above: the red bar shows attainment year 

emissions with base year controls and attainment year VMT, starts, and vehicle 

population, the green bar shows attainment year emissions with base year controls, 

VMT, starts, and vehicle population, and the blue bar shows attainment year emissions 

with attainment year controls, VMT, starts, and vehicle population. Based on the U.S. 

EPA guidance, if the blue bar is lower than the green bar, then the identified 

transportation control strategies and TCMs are sufficient to offset the growth in 

emissions.
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Figure 1. VOC Emissions* from On-Road Mobile Sources in 

the San Joaquin Valley Air Basin (2002 Base Year)

* Does not include resting or diurnal loss emissions
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Figure 2. VOC Emissions* from On-Road Mobile Sources in the

San Joaquin Valley for 1990 Base Year

* Does not include resting or diurnal loss emissions

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