Office of Transportation and Air Quality

EPA-420-B-12-053 

August 2012 

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

Purpose

The document is intended to provide guidance to Severe and Extreme ozone 

nonattainment areas on how to address Clean Air Act (CAA) section 182(d)(1)(A). This section 

of the CAA requires such areas to offset growth in emissions due to growth in vehicle miles 

traveled (VMT) through the implementation of transportation control strategies and 

transportation control measures (TCMs). This guidance is necessary due to a decision issued by 

the U.S. Court of Appeals for the 9th Circuit in a case related to the 1-hour ozone SIP for the 

South Coast area in California. 

Background

CAA section 182(d)(1)(A) applies to Severe and Extreme ozone nonattainment areas and 

requires that:

Within 2 years after November 15, 1990, the State shall submit a revision [to their state 

implementation plans (SIPs)] that identifies and adopts specific enforceable 

transportation control strategies and transportation control measures to offset any growth 

in emissions from growth in vehicle miles traveled or numbers of vehicle trips in such 

area and to attain reduction in motor vehicle emissions as necessary, in combination with 

other emission reduction requirements of this subpart, to comply with the requirements of 

subsection (b)(2)(B) 1 and (c)(2)(B) of this section (pertaining to periodic emissions 

reduction requirements). The State shall consider measures specified in section 108(f) of 

this title, and choose from among and implement such measures as necessary to 

demonstrate attainment with the national ambient air quality standards; in considering 

such measures, the State should ensure adequate access to downtown, other commercial, 

and residential areas and should avoid measures that increase or relocate emissions and 

congestion rather than reduce them. 

EPA has observed in prior final SIP approvals that section 182(d)(1)(A) contains three 

elements [i.e., 1) offsetting growth in motor vehicle emissions from growth in vehicle miles 

traveled or vehicle trips, 2) attaining reduction in motor vehicle emissions consistent with 

reasonable further progress (RFP) demonstrations, and 3) implementing measures as necessary to 

demonstrate attainment of the ozone national ambient air quality standards (NAAQS)] that can 

be divided into three separate SIP submissions that could be submitted on different dates. EPA 

explained in the SIP approvals that it views the elements of section 182(d)(1)(A) as distinct and 

separate from one another. The elements do not rely on one another in that they are either 

considered as a stand-alone element (in the case of the first element) or are considered in 

 

1 So in original. Probably should read “subsections (b)(1)(A)”. (Committee Print: Compilation of of Selected Acts 

Within the Jurisdiction of the Committee on Energy and Commerce. Clean Air Act Section 182(d)(1)(A). Page 182 

U.S. Government Printing Office. Washington, DC. 1993.)
2 

conjunction with other SIP elements (the 15% and post-1996 RFP demonstrations in the case of 

the second element and the attainment demonstration in the case of the third element). This 

document relates only to the first element addressed in section 182(d)(1)(A), referred to herein as 

the "VMT Offset requirement," not the second or third elements of CAA section 182(d)(1)(A).

EPA first issued guidance on the VMT Offset requirement in the April 1992 “General 

Preamble,” which advised states to first estimate on-road volatile organic compound (VOC) 

emissions starting in the base year through the area’s attainment year.2 Under this guidance, as 

long as a state’s SIP submission showed that on-road emissions did not increase from year to 

year, states could demonstrate that there was no increase in emissions due to growth in VMT. In 

such circumstances, it would not be necessary to include TCMs in the SIP, in order to meet the 

VMT Offset requirement of CAA section 182(d)(1)(A). Alternatively, if there was an upturn in 

emissions before the attainment year, those increased on-road emissions would need to be offset 

with reductions obtained through additional transportation-related measures in the SIP. 

In approving the VMT Offset demonstration submitted in connection with the 2003 South 

Coast 1-Hour Ozone SIP, EPA applied its longstanding interpretation of the corresponding CAA 

requirement that allowed a state to conclude that no further TCMs are necessary if aggregate 

motor vehicle emissions are projected to decline each year from the base year of the plan to the 

attainment year. EPA’s approval was then challenged in the U.S. Court of Appeals for the 9th 

Circuit. One aspect of the suit concerned EPA’s approval of the VMT Offset demonstration that 

showed compliance with the VMT Offset requirement by showing an annual decline in 

aggregate motor vehicle emissions for the area though the attainment year. The Court ruled 

against EPA in early 2011, saying in part that EPA should have required TCMs to be 

implemented to offset growth in emissions from growth in VMT, because in the Court’s view 

EPA incorrectly interpreted the phrase “growth in emissions” as meaning a growth in “aggregate 

motor vehicle emissions.” Association of Irritated Residents v. EPA, 632 F.3d 584, at 596-597 

(9th Cir. 2011), reprinted as amended on January 27, 2012. 

The following is intended to provide guidance to Severe and Extreme ozone 

nonattainment areas on how to address this CAA requirement in light of the Court’s decision. 

This guidance is not a final action, and is merely based on CAA requirements and does 

not create any new requirements. The CAA contains legally binding requirements. This 

document is not a substitute for those provisions and it is not a regulation itself. Thus, it does not 

impose legally binding requirements on EPA, or states, and may not apply to a particular 

situation based upon the circumstances. This guidance may be revised periodically without 

public notice. This guidance recommends how states and local government agencies might 

address the CAA section 182(d)(1)(A) VMT Offset requirement, taking into consideration the 9th

Circuit’s aforementioned decision. 

 

2

 See 57 Fed. Reg. 13,498, at 13,521-15,523 (April 16, 1992).
3 

The 9th Circuit’s Decision

In its February 2011 decision the Court determined that the question that it needed to 

address was “whether ‘any growth in emissions’ can mean any growth in aggregate motor 

vehicle emissions, or is unambiguous in meaning any increase in the level of emissions solely 

from VMTs.” The Court concluded that EPA’s longstanding guidance on the requirements of 

CAA section 182(d)(1)(A) gave meaning only to the portion of the provision that requires TCMs 

to be used if they are needed for RFP or attainment purposes and did not give meaning to the 

portion of the provision that “contemplates using TCMs to reduce VMT.” The decision included 

a review of legislative history for this CAA section. For example, the decision included 

language from the House Committee report which states that the baseline for determining 

“growth in emissions” should be established by calculating the “level of vehicle emissions that 

would occur if VMT held constant in the area.” (H.R.Rep. No. 101-490, pt. 1 at 242 (1990)) The 

Court concluded that in order to give meaning to all of the requirements in CAA section 

182(d)(1)(A) EPA should have required TCMs that offset the growth in emissions that was due 

to the increase in VMT in addition to requiring TCMs if they were needed for RFP or attainment 

purposes. However, even in purporting to reject EPA’s longstanding interpretation of the phrase 

“growth in emissions,” the Court acknowledged that “clean car technology” advances could 

result in there being no increase in emissions even in the face of VMT growth, which would then 

allow VMT to increase without triggering the requirement to adopt offsetting TCMs: “we cannot 

ignore the possibility that with advances in clean car technology, one day VMT could increase 

without a corresponding increase in emissions. If that happens, under the statute, EPA would not 

need to impose TCMs even though VMT increased.” Association of Irritated Residents v. EPA, 

632 F.3d 584, at 596-597 (9th Cir. 2011), reprinted as amended on January 27, 2012. 

Note that the Court held that “EPA should have required transportation control 

measures,” which are clearly defined in the CAA and in EPA’s implementing regulations. See 

CAA section 108(f) and 40 C.F.R. 51.100(r). However, the Court omitted any reference to 

“transportation control strategies,” which are not specifically defined in the CAA, but which 

under CAA section 182(d)(1)(A) are equally eligible to offset any growth in emissions resulting 

from growth in VMT. Similarly, EPA regulations do not explicitly define “transportation control 

strategies.” Instead, EPA’s regulations at 40 C.F.R. 51.100(n) broadly define “control strategy” 

to mean “a combination of measures designated to achieve the aggregate reduction of emissions 

necessary for attainment and maintenance of national standards, including, but not limited to, 

measures such as: [...] (6) Emission control measures applicable to in-use motor vehicles, 

including, but not limited to, measures such as mandatory maintenance, installation of emission 

control devices, and conversion to gaseous fuels; [. . .] (8) Any variation of, or alternative to any 

measures delineated herein.” Clearly, several “control strategies” under EPA regulations are 

transportation-related, and the regulations do not therefore on their face appear to restrict what 

kinds of measures might be eligible for treatment as “transportation control strategies” for 

purposes of section 182(d)(1)(A)’s VMT Offset requirement. 

In fact, in light of the Court’s statement that clean car technologies could advance such 

that there is no increase in emissions from growth in VMT and therefore no need to adopt TCMs 

for this purpose, the Court seems to sensibly recognize and imply that improvements in vehicle 

technology, motor vehicle fuels and other control strategies that are transportation-related might 
4 

reasonably be counted as offsetting “any increase in emissions due solely to VMT,” as the Court 

put it. This guidance suggests how these technology improvements might be included by states 

in the group of measures that the CAA refers to as “transportation control strategies” which may 

be used to offset growth in emissions from VMT growth.3 We now recommend that both 

transportation control strategies and TCMs should be included in calculations for the purpose of 

determining the degree to which any hypothetical growth in emissions due to growth in VMT 

should be offset. 

Revised Guidance

As noted above EPA’s earlier guidance advised states to estimate VOC emissions starting 

in the state implementation plan’s base year through the attainment year and, if there is ever an 

upturn in emissions, that emissions increase must be offset. Under the earlier guidance, states 

calculated on-road emissions for each year starting with the SIP’s base year through the area’s 

attainment year in order to determine if an upturn in emissions ever occurred. 

Under today’s revised guidance states would no longer need to calculate year to year 

changes in emissions. Instead the state would estimate emissions in only two years, the 

nonattainment area’s base year and its attainment year. We believe that states’ estimating 

emissions in these two years rather than in every year would be reasonable because examining 

the base year and attainment year would be consistent with the overall purpose of SIPs, which is 

to provide for attainment of the NAAQS, because of the long lead time necessary to achieve 

significant emissions reductions from adoption and implementation of transportation control 

strategies (such as new vehicle emissions standards or engine retrofit or replacement programs), 

and because the only other reasonable analysis years to evaluate would be the periodic milestone 

years (for RFP) and transportation-related requirements for those years are addressed separately 

in the second element of CAA section 182(d)(1)(A). The decision did not take up the issue of 

what temporal period should be used to determine whether emissions were being sufficiently 

offset. Rather, the Court merely referred to changed circumstances compared to “a prior year” 

without specifying which prior year, without being clear whether it was comparing year-to-year 

changes or a base year to a much later year change. 

The following paragraphs describe recommended calculations 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. A flow chart 

depicting the process described below is included in the appendix. 

The state would present the base year on-road VOC emissions. The base year on-road 

emissions should be based on VMT in that year and it should reflect all transportation control 

strategies and TCMs in place in the base year. This would include the vehicle emissions 

 

3 Based on the definition of "control strategy" found in 40 CFR 51.100(n) and the Court’s acknowledgement that 

“clean car technology” advances could result in there being no increase in emissions even in the face of VMT 

growth, "transportation control strategies" could include but would not be limited to: motor vehicle inspection and 

maintenance programs, reformulated gasoline, low Reid vapor pressure gasoline, and new vehicle emissions

standards (e.g., federal Tier 2 and California Low Emission Vehicle emissions standards and the fuel requirements 

associated with these regulations). 
5 

standards, state and local control programs such as inspection and maintenance programs or fuel 

rules, and any implemented TCMs that were already required by or credited in the SIP as of that 

base year. For the attainment year the state would present three emissions estimates as shown in 

the graph below, two of which would represent hypothetical emissions scenarios that would 

provide the basis to identify the “growth in emissions” due to growth in VMT, and one that

would represent projected actual motor vehicle emissions after fully accounting for projected 

VMT growth and emissions reductions obtained by all creditable TCMs and transportation 

control strategies. 

The first emissions calculation for the attainment year would be based on the projected 

VMT for that year, and assuming that no new transportation control strategies or TCMs have 

been put in place since the base year. This calculation demonstrates how emissions would 

hypothetically change if no new transportation control strategies or TCMs were implemented, 

and VMT was allowed to grow at the projected rate from the base year. In other words, this 

estimate would show the potential for an “increase in emissions due solely to VMT,” as the 

Court put it. This emissions estimate is shown as the red bar in the graph below, and represents a 

no–action-taken scenario. It should be noted that even though no new transportation control 

strategies or TCMs were hypothetically implemented and VMT was allowed to increase, 

emissions in the attainment year may be lower than those in the base year. This would be due to 

the fleet that was on the road in the base year gradually being replaced through fleet turnover 

with newer vehicles certified to the emissions standards that were in effect for new production in 

the area’s base year and were already accounted for in the SIP. 

The second emissions calculation for the attainment year would also assume that no new 

transportation control strategies or TCMs beyond those already credited were added or 

implemented after the base year and would also assume that there was no growth in VMT

between the base year and attainment year. This estimate would reflect the hypothetical 

emissions level that would have occurred had no further TCMs or transportation control 

strategies been adopted or implemented and had VMT levels “held constant,” in the Court’s 

words. This is shown as the green bar in the graph below, and, like the first estimate, emissions 

in the attainment year may be lower than those in the base year due to the fleet that was on the 

road in the base year gradually being replaced through fleet turnover. This emissions estimate 

would reflect a ceiling on the emissions that should be allowed to occur under the statute as 

interpreted by the Court in the attainment year because it shows what would happen under a 

scenario in which no new transportation control strategies or TCMs are put in place and VMT is 

“held constant” during the period from the area’s base year to its attainment year. While this 

estimate obviously would reflect a hypothetical status quo that is extremely unlikely to exist in 

reality, under the Court’s reasoning it is a necessary step in identifying the target level of 

emissions from which states would determine whether further TCMs or transportation control 

strategies would need to be adopted and implemented in order to remedy “any increase in 

emissions due solely to VMT” as shown by the first calculation. The comparison of these first 

two calculations would thus identify whether there is a hypothetical growth in emissions from 

growth in VMT that would need to be offset. 

Finally, the state would present the emissions that are actually expected to occur in the 

area’s attainment year. This estimate would be based on the VMT that is expected to occur in 
6 

the attainment year (i.e., the VMT level from the first estimate) and all of the transportation 

control strategies and TCMs that are in reality expected to be in place and for which the SIP will 

take credit in the area’s attainment year, including any TCMs and transportation control 

strategies adopted and credited since the baseline year (i.e., the estimate of such measures that 

existed prior to the baseline year, plus any additional measures that come into place by the 

attainment year). This is shown as the blue bar in the graph below. If this emissions estimate is 

less than or equal to the emissions ceiling that was established in the second calculation, the 

credited transportation control strategies or TCMs for the attainment year would be sufficient to

offset the hypothetical growth in emissions represented by comparing the first two calculations. 

If, instead, the estimated attainment year emissions are greater than the ceiling which was 

established in the second calculation, the state would need to implement additional transportation 

control strategies or TCMs to further offset the growth in emissions and bring the actual 

emissions down to at least the “had VMT held constant” ceiling estimated in the second

calculation. 

When a state makes a SIP submittal that addresses the section 182(d)(1)(A)’s VMT 

Offset requirement, that submittal should include the calculations described above and it should 

clearly identify the transportation control strategies and TCMs that were included in the 

calculations for the base year and the attainment year. If any additional transportation control 

strategies or TCMs are required in order to offset growth in emissions, those transportation 

control strategies and TCMs should also be clearly identified and distinguished from the list of 

strategies and measures included in the initial calculations for the base year and the three 

scenarios required for the attainment year. 

Figure 1

Graphical Depiction of the Results of the Calculations for the Base Year and Attainment Year 

for a Hypothetical Nonattainment Area 

 - 

100 

200 

300 

400 

500 

600 

700 

Base year Attainment Year

Base year emissions

Emissions assuming no 

new measures with VMT 

growth

Emissions assuming no 

new measures and no 

VMT growth

Actual Emissions with 

controls and VMT growth
7 

Appendix 

Flow Chart Describing the Steps in the Process for Determining if Additional Transportation 

Control Strategies or TCMs are Necessary to Offset Growth in Emissions Due to Growth in 

VMT