ENVIRONMENTAL PROTECTION AGENCY
[AMS-FRL-4115-8]
VMT Forecasting and Tracking Notice of Availability
AGENCY: Environmental Protection Agency (EPA).
ACTION: Notice of Availability of Section 187 VMT Forecasting and Tracking
Guidance.
SUMMARY: Today's action provides notice of available guidance on how to forecast and
track vehicle miles traveled (VMT) in Moderate and Serious carbon monoxide (CO) non-
attainment areas with design values greater than 12.7 ppm at the time of classification. This
guidance is required by Section 187(a) of the Clean Air Act Amendments of 1990 (CAAA).
The guidance states that estimates of actual annual VMT in areas subject to the
Section 187 requirements should be obtained from the Highway Performance Monitoring
System (HPMS). A state containing such an area should commit in its State
Implementation Plan (SIP) to follow the Department.of Transportation, Federal Highway
Administration guidance in sampling for HPMS, with separate urbanized area sampling for
the affected areas in 1993 and later calendar years. The HPMS VMT estimates will be used
to track actual VMT.
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The guidance also states that VMT forecasts should be based on a validated
network-based travel demand modeling process meeting certain requirements, except that in
Moderate areas without a currently validated travel demand model that meets these
requirements, VMT forecasts may be based on the HPMS.
Further, the guidance discusses the criteria for determining whether actual VMT or
an updated forecast is greater than a prior forecast.
Finally, the guidance discusses the linkage between forecasted VMT and the several
CO emission inventories required by the Amendments.
As required by Section 187 of the CAAA, the guidance was developed in
consultation with the U.S. Department of Transportation.
TO OBTAIN A COPY OF THE GUIDANCE: Please send requests by FAX or by mail to
Natalie Dobie. FAX: (313) 668-4368 or FTS 374-8368. Mailing address: Test and
Evaluation Branch, U.S. EPA Motor Vehicle Emission Laboratory, 2565 Plymouth Road,
Ann Arbor, MI 48105.
FOR FURTHER INFORMATION CONTACT: Natalie Dobie or Mark A. Wolcott, Test
and Evaluation Branch, U.S. EPA Motor Vehicle Emission Laboratory, 2565 Plymouth
Road, Ann Arbor, MI 48105. Telephone: (313) 741-7812 or (313) 668-4219, FTS 374-
8812 or 374-8219.
SUPPLEMENTARY INFORMATION: Section 187(a)(2)(A) of the CAAA requires that
states containing a Moderate and/or Serious CO non-attainment area with a design value
greater than 12.7 ppm at the time of classification must forecast vehicle miles traveled in the
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non-attainment area for each year before the attainment year. The first forecast is due no
later than November 15,1992. The VMT forecast for the attainment year is the basis for
the area's attainment demonstration. The intermediate forecasts act as milestones for
progress towards attainment.
Annual updates of the annual VMT forecasts must be submitted to EPA along with
annual reports regarding the extent to which such forecasts have proven to be accurate.
These reports must contain estimates of actual vehicle miles traveled in each year for which
the forecast was required.
Although the Section 187 VMT Forecasting and Tracking Guidance does not
identify the required contingency measures to be implemented if a VMT forecast is
exceeded by either actual VMT or an updated forecast nor does it discuss the process for
their implementation, the contingency measures and the implementation process will be
discussed in future EPA guidance.
Dated: March 12. 1992 (sipiedV
William K. Reilly
Administrator
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U.S, Department of
Transportation
Office of the Secretary
of Transportation
Office of Assistant Secretary
DEC 23 1991
400 Seventh St., S.W.
Washington. D.C. 20590
Refer to: HEP-22
Mr. Richard D. Wilson
Director, Office of Mobile Sources
US Environmental Protection Agency
Washington, D.C. 20460
Dear Mr. Wilson:
I am writing in response to your October 30, 1991, letter
transmitting the VMT Forecasting and Tracking Guidance required
by Section 187 of the Clean Air Act Amendments of 1990. This
letter is our formal acknowledgement that the consultation
required under the Clean Air Act in the preparation of this
guidance has indeed taken place.
As you know, EPA and DOT have been working diligently in the
preparation of this guidance since March 1991. This effort has
resulted in a product that we believe addresses the Section 187
requirement and represents good planning practice. The "Final
Draft" dated November 1991 (with subsequent modifications to
provide for (1) a phase-in for improved VMT estimation over time
and (2) alternative approaches to estimating transit travel),
represents EPA/DOT agreement on appropriate methods for VMT
estimating and forecasting.
From the outset, both EPA and DOT have been concerned that the
methods and procedures contained in the guidance appropriately
consider the analytical and resource capabilities of States and
MPOs, and the state-of-the-practice. This is of particular
concern since these methods for estimating VMT will be applicable
to both serious and above Ozone nonattainment areas as well as
the CO nonattainment areas specified in the guidance. In
addition, we wanted to make the best use of data collection and
analyses already in place to keep additional costs for States and
MPOs to a minimum. We also wanted to use a methodology which
provided consistent validity across "the country. The use of the
Highway Performance Monitoring System (HPMS) as a base achieves
these objectives in most cases.
While DOT believes that the methods in the Guidance represent
"best practice," not all States and MPOs are currently up to
this level of application. Some areas will require some
flexibility and time to upgrade to existing procedures. For
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«.
example, several States and MPOs have voiced concern over the -
baSffor ?SaCy °£ l?cal traffic counting progra^and LMS as a
basis for the nonattainment area VMT estimates, as well as the
reSonir^^H1 aSSUmed in this data by the guidance? In ~
response to these concerns, we fully support the "phasinq-in" of
lJ95lre?h?r»nhar -er1S f°* *stimatedVMT for 199? 19^4 and
1995. _ This "phase-in" recognizes that initially there will be
significant unknowns, but that data collection and analytical
SSSS'JhS1^ imProved over time. WhilSwe canno^be
certain that a 3 percent variance in the HPMS-based VMT estimate
is achievable^by 1995 due to uncertainties involved irTthe
^
the
We look forward to a continued close association with
K^r^ 5heSS and °ther initiative, Elated
5 SK *""*«>* EPA has indicates that additional
'uKla ?hid?^Se W^X bS devel°Ped "to assist States Snd
our support and
Sincerely,
Canny
Deputy Assista£"secretary
for Policy and Regulatory
Affairs
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. TABLE OF CONTENTS
1.0 PURPOSE, BACKGROUND, AND GENERAL APPROACH.
1.1 Purpose ........ ..... ......
... ..... ......
L2 s^ct;!0^
the Clean Air Act Amendments of 1990 ....... . ....
1.3 General Approach. ............ ........ ........ -
2.0 SUMMARY OF GUIDANCE. .......
2.1 Actual Annual Vehicle Miles Traveled.. ..........
2.2 Forecasted Vehicle Miles Traveled... ... ....... . ......... ... 1Q
2.2.1 Serious Areas... .......
2.2.2 Moderate Areas ........ ....... ;
2.3 Determining Whether a Forecast Has Been Exceeded ..... .... ........ U
3.0 1990 VMT ESTIMATION AND VMT TRACKING ........ 13
3 . 1 Period and Geographic Coverage . . .
3.2 Highway Performance Monitoring Systi
3.3 Local Functional System VMT Estimates ^
.............. > ............ < ......... 16
3.4 VMT Estimates C)utside of ^Federal Aid Urbaruze^
.13
em 14
3V6 Areas Using Network-Based Models to Estimate 1990 VMT
3.7 VMT Estimation for Localized Non-Attainment Problem....
4.0 VMT FORECASTING FOR 1992 SIP SUBMITTAL
""
/
i«
" .......................... Io
4.1 Forecasting Years...... ..... .......... .
. " ...... .............. ...... ..... ..... .........18
4.2 Network-Based Travel Demand Modeling Process Methodology............. 19
4.3 Historical Area-Wide VMT Method ........... ................. , 2{
4.4 Safety Margin..
" .................. ' ................... '-. ...... -... ...... ...22
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5.0 REVISING A FORECAST 23
5.1 Network-Based Travel Demand Modeling Process Methodology 23
5.2 Highway Performance Monitoring System 23
6.0 CONTINGENCY MEASURES 24
7.0 ANNUAL REPORTING PROCEDURES 25
7.1 Requkement 25
7.2 Responsibility 26
7.3 Process 26
7.4 Report Content 26
7.4.1 General Content ...26
7.4.2 Highway Performance Monitoring System-1990 B ase and
Tracking VMT 26
7.4.3 Network-B ased Travel Demand Modeling Proces s
Methodology 28
7.4.4 Highway Performance Monitoring System-Based Forecasts 32
7.4.5 Record Keeping Requirements 32
8.0 AREAS RECEIVING EXTENSIONS UNDER SECTION 186(a)(4) 33
9.0 RECLASSIFICATION OF MODERATE AREAS UPON FAILURE f O
ATTAIN 33
10.0 INVENTORIES 34
10.1 Guidance Applicable to Specific Non-Attainment Area Inventories 34
10.1.1 1990 Inventory [187(a)(D] 34
10.1.2 "Periodic Inventories" [187(a)(5)] 34
10.1.3 "Specific Annual Emission Reductions" [187(a)(7)] 34
10.1.4 Attainment Demonstration Inventory : 34
10.1.5 Severe Area Milestone [187(d)( I >] 34
10.2 Guidance Applicable to All Inventories in CO Non-Attainment Areas
with Design Values Greater than 12.7 ppm : 35
11.0 AUTHORITY 36
12.0 TIMELINE 36
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.1.0 PURPOSE, BACKGROUND, AND GENERAL APPROACH
1.1 Purpose
This guidance is required by Section 187(a) of the Clean Air Act Amendments of 1990
(CAAA). It offers the Environmental Protection Agency's (EPA's) recommendations on how to
forecast and track vehicle miles traveled (VMT) in Moderate and Serious carbon monoxide (CO)
non-attainment areas with design values greater than 12.7 ppm at the time of classification.
The purpose of this guidance is to help states prepare Stale Implementation Plan (SIP)
revisions that EPA can readily propose to approve as meeting the requirements of the CAAA. If a
state adheres to the guidance, EPA will propose approval of its SIP. A state intending to depart
from the guidance, however, should show that the alternative approach it proposes is technically
sound and adequate to meet the requirements of the CAAA. EPA will review SIP submittals from
such states on a case-by-case basis to determine whether they do in fact comply with the CAAA
requirements. Stages are encouraged to obtain EPA approval before using methods other than
those specified in this guidance, in order to avoid later problems.
Each state may assign its responsibaities, as specified in this guidance, to various state
organizations as it sees fit. EPA will coordinate its responsibilities under the guidance with the
Federal Highway Administration.
This guidance does not establishor affect legal rights or obligations. It does not establish a
binding norm, and it is not finally determinative of the issues addressed. Agency decisions in any
particular case will be made by applying the applicable law and regulations to the specific facts of
that case. In any proceeding in which the policy articulated in this guidance may be applied, the
Agency will thoroughly consider the policy's applicability to the facts, the underlying validity of '
the policy, and whether changes should be made in the policy based on submissions made by any
person.
L2 Overview pf Carbon Monoxide Air Quality Planning Requirements of the Clean Air A^
Amendments of 1900
Under the Clean Air Act Amendments of 1990 states have the responsibility to inventory
emissions contributing to violations of the National Ambient Air Quality Standards (NAAQS), to
track these emissions over time, and to ensure the implementation of control strategies that reduce
emissions and move areas toward attainment.
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The CAAA establish non-attainment area classifications and control program requirements
ranked according to the severity of a carbon monoxide non-attainment area's air pollution problem.
There are two CO non-attainment classifications: Moderate and Serious. In addition, for
the purposes of Section 187(a)(2)(A), "Vehicle Miles Traveled," the subject of this guidance, the
Moderate classification is divided into two sub-classifications on the basis of design value: 12.7
pprn and lower, and greater than 12.7 ppm. This guidance applies to CO non-attainment areas
with design values greater than 12.7 ppm.1
1 The areas currently affected are the following. (For a complete listing of non-attainment area classifications and
designations, see the Federal Register Notice "Designation of Areas for Air Quality Planning Purposes" published on
November 6,1991.) a
Area Name
Anchorage, AK
Denver-Boulder, CO
Fresno, CA
Las Vegas, NV
Los Angeles South Coast Air Basin, CA
New York-N. New Jersey-Long Island, NY-NJ-CT
Prove, UTb
Seattle-Tacoma, WA
Spokane, WA
Design Value
(ppm)
13.1
16.2
13.0
14.4
23.4
13.5
15.8
13.4
13.8
Classification
Moderate
Moderate
Moderate
Moderate
Serious
Moderate
Moderate
Moderate
Moderate
8 The attainment designation for the area encompassed by Jefferson County, OH, Brooke County, WV, and Hancock
County, WV is not final. At the date of enactment of the CAAA, the area was designated unclassifiable/attainment, but
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Section 187(a) requkes Moderate CO non-attainment areas to submit a comprehensive,
accurate, current inventory of actual emissions from all sources, as described in Section 172(c)(3).
The inventory is defined as the base year inventory and is for the calendar year 1990. EPA has
instructed states to submit draft base year inventories between January and March of 1992. The
inventory must report actual CO emissions during the peak CO season for the non-attainment
area.2 All stationary point and area sources and all highway/non-highway mobile sources3 must be
included in the inventory.
Section J.87(a)(2)(A) requkes that states containing a Moderate and/or Serious CO non-
attainment area with a design value greater than 12.7 ppm at the time of classification must forecast
vehicle miles traveled in the non-attainment area for each year before the attainment year. The first
forecast is due no later than November 15,1992. The VMT forecast for the attainment year is the
basis for the area's attainment demonstration. The intermediate forecasts act as milestones for
progress towards attainment.
Annual updates of the annual VMT forecasts must be submitted to EPA along with annual
reports regarding the extent to which such forecasts have proven to be accurate. These reports
shall contain estimates of actual vehicle miles traveled in each year for which the forecast was
requked.
these states and EPA are reviewing whether to confirm or reverse this designation and will publish a separate notice to that
effect. (Federal Register. Vol. 56, No. 215, November 6, 1991.)
Only the city of Provo was designated non-attainment by operation of law under Section 107(dXl)(Q of the CAAA,
and the rest of Utah County remained unclassifiable/attainment. However, the state and EPA are reviewing whether to
confirm or reverse that designation under the process set out under Section 107(d)(4XA) and will publish a separate notice to
that effect. (Federal Register. Vol. 56, No. 215, November 6, 1991.)
2 For most CO non-attainment areas, this will be the winter months of November, December, 1990 and January,
1991. -
3 All states except California should use an updated version of the mobile source emission factor model
(MOBILE4.1) to estimate mobile source emissions. The updated model replaces MOBELE4 and should be used in
the development of all 1990 base year inventories.
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The statutory requirement for annual VMT reports suggest;? that Congress intended the
reports, and any action that they indicate is necessary, to be completed reasonably soon after the
close of the reporting period. This guidance, therefore, specifies that annual reports on actual
VMT and subsequent forecasts should be submitted annually no later than each September 30.
Most states now submit their HPMS data reports to FHWA around June 30, and the additional
three months will allow states to respond to FHWA data validity questions and to prepare updated
projections, projected-versus-actual comparisons, and other elements of the report for EPA. The
first forecast includes the years 1993 and each year prior to the year of attainment. Annual reports
must contain estimates of actual VMT in the non-attainment area in each year for which a forecast is
required.
Section 187(a)(3) requires that a state subject to the VMT forecasting/tracking provision
must provide in its SIP for the implementation of contingency measures if the annual estimate of
actual VMT or a subsequent VMT forecast exceeds the most recent prior forecast of VMT or if the
area fails to attain the CO NAAQS by the attainment date. These contingency measures must be
adopted and enforceable in the SIP and must take effect immediately, without further action by the
State or the Administrator, following such an event.
Section 187(a)(4) is a savings provision for existing vehicle inspection/maintenance (I/M)
programs.
Section 187(a)(5) requires Moderate CO non-attainment areas to submit periodic (historical)
inventories. The first periodic inventory is due no later than September 30, 1995; subsequent
inventories are due every three years thereafter until the non-attainment area is redesignated to
attainment. The periodic inventory must meet the same requirements as those that apply to the base
year inventory.
Section 187(a)(6) requires Moderate CO non-attainment areas with a design value greater
than 12.7 ppm to implement an enhanced I/M program in an urbanized area with a 1980 population
of 200,000 or more.
Section 187(a)(7) requires that a state containing a Moderate non-attainment area with a
design value greater than 12.7 ppm demonstrate that the area will comply with the NAAQS by
December 31, 1995. The demonstration must include specific annual emission reductions
necessary to achieve attainment by that date.
Section 187(b)(l) requires a state containing a Serious CO non-attainment area to make the
same submissions as a state containing a Moderate non-attainment area.
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Sections L87(a)(2)(B) and 187(b)(2) require Serious CO non-attainment areas and Denver,
Colorado to adopt and implement enforceable transportation control measures (TCMs) to offset any
growth in emissions from growth in vehicle miles traveled and numbers of vehicle trips, and to
achieve reductions in mobile source emissions as are necessary in conjunction with other control
measures to comply with the periodic emission reduction requirements of the CAAA. Section
187(b)(2) also requires Serious CO areas only to adopt an employer-based trip reduction program.
Section 187(c)(2) allows the Administrator to waive any requirements that pertain to
transportation controls for CO non-attainment areas in which mobile sources do not contribute
significantly to CO levels in the area.
Section 187(d) requires Serious CO non-attainment areas to submit to EPA by March 31,
1996 a demonstration that the emission reductions anticipated to occur by December 31,1995 as
specified in the 1992 State Implementation Plan revision have, indeed, occurred. Serious CO non-
attainment areas that miss this milestone must submit to EPA a SIP revision to implement an
economic incentive and transportation control program sufficient to achieve the annual emission
reductions specified in the SIP by the attainment date. This SIP revision is due within nine months
of a failure to make the demonstration or of EPA's notification of an inadequate demonstration.
Sections 187(b)(3) and 21 l(m) together require that a state containing a CO non-attainment
area with a design value above 9.5 ppm based on 1988 and 1989 data must require that, by
November 15, 1992, fuel sold or supplied or offered for sale or supply within the larger of either
the Consolidated Metropolitan Statistical Area (CMSA) or Metropolitan Statistical Area (MSA) in
which the non-attainment area is located contain 2.7 percent oxygen by weight during the period
of high CO concentrations, as determined by the Administrator.
Section 246(a)(2)(B) requires all CO non-attainment areas with a 1980 population of
250,000 or more and a design value of 16.0 ppm or greater to provide for clean-fuel vehicle fleet
programs no later than May 15,1994. The programs must require a specified percentage of fleet
vehicles in model year 1998 and thereafter to be clean-fuel vehicles and use clean alternative fuels
when operating in the non-attainment area.
1.3 General Approach
Air quality forecasting and attainment planning require an estimate of emissions in a certain
geographic area in a past period with a known air quality, and forecasts of future emissions under
various alternative strategies designed to reduce emissions. Motor vehicles are the dominant
source of CO in most non-attainment areas. CO emissions from highway motor vehicles are a
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product of gram per mile emission factors (reflecting periods of both travel and parking) and the
number of miles driven.. The emission factors in turn are a function of trip length and traffic flow,
with average traffic speed being the most common indicator of flow.
While trip length and traffic flow characteristics also influence emissions and are to some
extent sensitive to influence by clean air programs, the more VMT growth there is in an area, the
more effort is requked to reduce both per vehicle and stationary source emissions to attain the
ambient CO standard by the required deadlines. Consequently, the CO attainment plan is built
largely around forecasted VMT in the attainment year.
However, future VMT is dependent on trends in regional population and economic growth,
on land and transportation system development patterns, and on the effectiveness of measures to
foster the use of alternative modes of transportation. Forecasting VMT is therefore subject to
uncertainty.
A feature of the Clean Air Act Amendments of 1990 is annual VMT tracking in CO areas in
the period prior to the target attainment date. This is intended to spot situations in which the actual
VMT growth occurring in the non-attainment area is higher than the forecasted VMT growth used
in the attainment demonstration. Such a situation may arise from higher than expected population
'or economic growth, or lower than expected success at promoting alternative modes of travel.
Under these circumstances, attainment is in jeopardy, and action beyond that originally
contemplated in the demonstration might be necessary. Such actions include further reducing VMT
growth and per mile vehicle emissions, as well as further controlling stationary emissions sources.
Because of the safety-net role played under the CAAA by a good tracking system and
contingency measures, uncertainty in the initial VMT forecast is of somewhat less concern than it
otherwise might be, since deviations from the forecast can be detected and mid-course corrections
can be made to preserve the attainment date. This guidance, therefore, places as much emphasis on
a well-defined and quality-assured tracking method as it does on valid forecasting methods. In
particular, the guidance specifies the use of systematic traffic ground counts as the underlying data
for estimates in the future of actual VMT, at least in the urbanized airea. This method is considered
by EPA to be superior in terms of both practicality and effectiveness to other methods such as
driver surveys, odometer data, registration counts, fuel sales, annually validated network models,
etc.
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In preparing this guidance, EPA encountered two views among interested parties regarding
how ground counts should be used to estimate actual travel in a year just completed. One view
supported the approach that has already been institutionalized in the Federal Highway
Administration's Highway Performance Monitoring System. In this approach, traffic counts taken
at various points on an urban area's road network are directly expanded into an estimate of area-
wide VMT using statistics on the number of roadway miles associated with each sampling point.
The other view supported the use of network-based transportation models, which
theoretically provide more detail on the location, sources, and purposes of travel. While network-
based models begin with only indirect indications of VMT (for example, number of households,
household locations, and household trips per day by purpose), their final results are generally
validated via comparison to actual ground counts at selected sites, usually sites on major traffic
corridors. However, annual updates of household and other input data and annual validation
against traffic counts would be too resource intensive to be practical. Therefore, EPA has chosen
to specify the use of the HPMS approach in this guidance for purposes of tracking 1993 and later
VMT.
Estimating 1990 VMT is a different issue because some areas did not make as full a set of
HPMS ground counts as they will be able to in 1993 given this guidance as advance notice, and
because validating a network-based model for one historical year is a practical possibility. EPA
therefore considered including as an option in the guidance the use of network models to define
1990 VMT, provided that demographic inputs are properly updated to 1990 and the model is
validated against 1990 ground counts. However, this method was not considered to be viable for
most areas due to the general disrepair of a large number of network models. Areas should use
this method only if their network model is particularly strong and their 1990 HPMS data are
particularly weak, and only after consulting with EPA.
.- Since HPMS will be used to track VMT after 1990, areas using a network model to
estimate 1990 VMT must accept the risk entailed in comparing data derived from two different
estimation methods. If the 1990 VMT estimate from the model is not consistent with later HPMS
data, the discrepancy may not be discovered until the later HPMS data are reported, and
adjustments will have to be made.
For forecasting VMT, network models were chosen as the best method. Though these
models are not considered to be a superior source of historical area-wide VMT, if they are well
validated and if they use an equilibrium approach to allocating trips, they are considered to be the
best predictor of growth factors for VMT forecasts.
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For all areas, estimates of actual 1993 and later vehicle miles traveled should be derived
from traffic ground counts consistent with the existing Highway Performance Monitoring System.
Since participation in this system is already a requirement of the Federal Highway Administration
(FHWA), this approach will involve minor costs above those imposed in the same time period by
the FHWA requirement.4
Moderate areas, which need to forecast VMT only through 1995, may use a simple,
liistorically based extrapolation method, if a better method is not locally available. The detailed
guidance statement that follows provides flexibility for cases in which the accuracy of the historical
data is suspect or there are other factors that would discredit this extrapolation method. Serious
areas that have not obtained an exemption under Section 187(c)(2) based on stationary source
emissions, a group that probably will comprise only the South Coast Air Basin of California,
should use a demographically based transportation demand model to forecast VMT growth factors
through 2000.
A state may adjust its VMT forecast upward without limit, if it considers a higher forecast
more accurate than that developed under this guidance. Also, if a state adopts new or strengthens
existing transportation control measures, it may adjust its VMT forecast downward to the degree
that the proposed TCMs will change VMT, provided that the effect: of such measures is based on
sound analytical techniques and is clearly documented in the SIP. EPA will disseminate
information on the VMT reduction benefits of TCMs as it is developed by EPA and other
organizations active in the area.
The CAAA also require updated forecasts each year. EPA interprets this to be a
Congressional desire to make sure that the State Implementation Plan is based on the best VMT
information available.
In general, economic factors should inform long-term VMT forecasts when an area uses
land use and transportation network travel demand models to forecast VMT.5 This guidance
allows such an approach.
4 FHWA is implementing improvements that will add to the reliability of the ground count method in the period
in question. States are free to exceed the FHWA requirements.
5 Metropolitan Washington, D.C., metropolitan Chicago, IL, and the South Coast Air Quality Management
District around Los Angeles, CA currently rely upon large forecasting models that explicitly use economic variables.
8
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This guidance only addresses VMT forecasts in CO non-attainment areas with design
values greater than 12.7 ppm. CO areas with design values at or below 12.7 ppm are not required
to forecast VMT or demonstrate attainment. This guidance does not address requirements for VMT
forecasts and tracking in ozone non-attainment areas. Nor does it address VMT forecasts made
under the conformity provisions of the CAAA. Also, this guidance does not address issues of
speed and other vehicle operating parameters. These topics will be addressed in other guidance
documents and/or other Federal Register notices and/or rules.
2.0 SUMMARY OF GUIDANCE
2.1 Actual Annual Vehicle Miles Traveled
A state containing a Moderate and/or Serious CO non-attainment area with a design value
greater than 12.7 ppm at the time of classification should commit in its State Implementation Plan
to sample each Highway Performance Monitoring System facility class/volume group separately
for each such CO non-attainment area, starting no later than January 1,1993. This sampling is to
be done fii accordance with die Department of Transportation, Federal Highway Administration's
HPMS guidance, as described in:
U.S.D.O.T.Code
M 5600.1A
M 5600.1 A, Chg. 1
M 5600.1 A, Chg. 2
(Deleted by Chg. 3)
M 5600.1 A, Chg. 3
Title
Highway Performance Monitoring System (HPMS) Field Manual
-r- :...':, ..^ ' ,_; _-.:... _.-.. ^ . . , . . . :.-; :_ _.' .
Highway Performance Monitoring System (HPMS) Field Manual Updates
Highway Performance Monitoring System (HPMS) Field Manual
-
Highway Performance Monitoring System (HPMS) Field Manual
and the traffic monitoring guidance described in:
the Traffic Monitoring Guide. June, 1985, U.S. Department of Transportation, Federal Highway
Administration, Office of Highway Planning,
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for the purposes of:
1. estimating 1990- actual area-wide VMT in the designated VMT Tracking Area. Methods
other than HPMS may be used to estimate that portion of 1990 VMT that occurs outside of
the Federal Aid Urbanized Area (FAUA).6 (A state that does not sample each FAUA
separately and cannot supplement its HPMS data with other counts not reported to HPMS
but has a well-maintained network model that is validated with 1990 ground counts will
have the flexibility to use the network model rather than HPMS to estimate 1990 VMT.)
2. estimating 1993 and later calendar years' actual area-wide VMT in the designated VMT
Tracking Area. These estimates of actual area-wide VMT will be used in tracking both
actual VMT and calculated emission inventories. Methods other than HPMS may be used
to estimate that portion of 1993 and later VMT that occurs outside of the FAUA.
Under certain conditions, a state with a localized CO non-attainment problem may use an
alternative to HPMS for estimating VMT, if the alternative is documented and justified in the SIP.
2.2 Forecasted Vehicle Miles Traveled
All states containing Moderate and/or Serious CO non-attainment areas with design values
greater than 12.7 ppm at the time of classification must forecast annual VMT for each year from
1993 until the year in which the SIP forecasts attainment.
2.2.1 Serious Areas
All states containing a Serious CO non-attainment area7 should forecast VMT in the VMT
Tracking Area by applying growth factors based on a validated network-based travel demand
modeling process (the "Network Travel Demand Model Method") to the actual annual 1990 VMT
described in Section 3.0, "1990 VMT Estimation and VMT Tracking." Details of this application
are described in Section 4.2, "Network-Based Travel Demand Modeling Process Methodology."
6 The Federal Aid Urbanized Area is the area within the boundary jointly developed by state and local officials and
approved by the Department of Transportation Federal Highway Administration to serve the federal aid highway
program needs and requirements. Boundary maps,are available from state Departments of Transportation and FHWA
Division offices.
7 Only the Los Angeles South Coast Air Basin non-attainment area is so designated.
10
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2.2.2 Moderate Area$ :
Ail states containing a Moderate CO non-attainment area with a design value greater than
12.7 ppm at thetime of classification should forecast VMT in the VMT Tracking Area by the
method just described for Serious CO areas if validated travel demand models are currently
available or if such modelscould be.made available intime to allow the required SIP revisions and
submissions. ,-
If the lead planning agency for a Moderate CO area, in consultation with appropriate other
state and local organizations, determines that avalidated travel demand model is currently
unavailable and that such a model cannot be made available in time to allow the required SIP
revisions and submissions, then the state may submit a request to the EPARegional Administrator
foran EPA commitment topropose approval of a SIP based on the Historical VMT Method,
discussed in Section 4.3, "Historical Area-Wide VMT Method." The EPA Regional Administrator
will review the request in consultation with the Federal Highway Administration Regional Office
and will attempt to respond to the request within 30 days.
A state that uses an alternative to HPMS to estimate and track VMT may base its VMT
forecasts on growth factors derived from the historical data collected for the alternative program.
2.3 Detemiining Whether a Forecast Has Been ETCS?^
EPA has determined, in consultation with the Department of Transportation, that there is a
statistical variability in the*stimates of actual annual VMT generated through HPMS. Since
- JS?^^^ the
,.,. ' ° conc
exceeded the most
the statistical^ia^Iiry jn tte accuracy of the numbers themselves. Although EPA is confident
that this statisti^^riabairy exists and always will, EPA is not certain of the exact magnitude of
me variability. Pre^^ the variability of HPMS estimates and forecasts
based on recent traffic counts is five percent. However, since EPA expects states to improve their
HPMS programs over the next few years in response to FHWA guidance and this EPA guidance,
EPA anticipates mat the variability will be reduced to three percent.
n
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Thus, EPA believes it is appropriate to allow a margin of error of 5.0 percent for VMT
comparisons made in 1994 based on HPMS data collected for 1993, a margin of 4.0 percent for
VMT comparisons made in 1995 based on HPMS data collected for 1994, and a margin of 3.0
percent for VMT comparisons made in 1996 and thereafter based on HPMS data collected for 1995
and later years.
So, in 1994, the estimate of actual VMT for 1993 will be considered to exceed the most
recent prior forecast, if the estimate of actual VMT is more than 5.0 percent greater than the prior
forecast of 1993 VMT submitted by November 15, 1992. In 1995, the estimate of actual 1994
VMT will be considered to exceed the most recent prior forecast, if the estimate of actual VMT is
more than 4.0 percent greater than the prior forecast of 1994 VMT reported in 1994. In 1996 and
later years, an estimate of actual VMT will be considered to exceed the most recent prior forecast if
the estimate of actual VMT exceeds by more than 3.0 percent the most recent prior forecast for the
same year.
The same margin of error applies in each year for comparisons of an updated forecast to the
most recent prior forecast. For example, in a Moderate area that forecasts VMT through 1995, a
prior forecast will be considered to be exceeded in 1994, if either the 1994 or 1995 updated VMT
forecast is more than 5.0 percent greater than the previous forecast for the corresponding year,
submitted by November 15,1992. For a Moderate area making comparisons in 1995, its updated
VMT forecast for 1995 will be considered to exceed the prior forecast for that year, if the updated
forecast is more than 4.0 percent above the prior forecast.
However, it is possible that both the estimate of actual VMT and the updated VMT forecast
could routinely exceed the most recent prior VMT forecast. Since each such revised forecast
becomes the VMT baseline for triggering contingency measures, the application of a margin of
error every year could allow the forecasts to increase without bound, without ever triggering
contingencies.
In light of EPA's uncertainty as to the exact magnitude of the statistical variability in VMT
calculations, and EPA's concern about the implications for SIP planning presented by the
potentially uncontrolled VMT growth that can result from the application of a statistical error band
every year, EPA believes that a cap must be imposed to prevent VMT estimates and forecasts from
exceeding a defined margin above the VMT forecast relied upon as the basis of the approved
attainment demonstration for a non-attainment area. Thus, while EPA believes that it is appropriate
to allow areas the benefit of the 5.0,4.0, or 3.0 percent variability, EPA believes that it is
12
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appropriate only as long as, cumulatively, estimates of actual VMT or VMT forecasts never exceed
bynetha,5.0pe«
. In practice, then, there are two ways in *h an estimate of actu^
forecast can be found to exceed a prior forecast Individual yearly comparisons can resultin an
exceedance of the prior forecast by more than the prescribed percentage for that year and
exceedances can accumulate so.that, cumulatively, they exceed the 5.0 percent "exceedance "
budget", which is based on the attainment demonstration forecast. So, even though actual VMT or
an updated forecast remains within the errortand around the most recentprior forecast for a
particular year, the individual exceedance for that year plus the exceedances accumulated over
previous years could amount to more than 5-Opercent above me forecast used m me attainment
demonstration, thus triggering the automatic contingency measures. :
3.0 1990 VMT ESTIMATION AND VMTTRACKING
Period and Geography
neededibrmventories and
factors. -.-..;
ion of Section 187(a)(2)(A) on annual VK^ since mis is
fT estimates for other spatial and temporalxtesohitioris are
ill be calculated from the annual VMT by the use of^djustment
riaries of tte CO non-attai
- ^^omi^iiiiM?a^^
:S»Sfea;iO/Cff-^^iSi-!
i cannot spatially resolve VMT within t
^AWUrbanized Area and since the Federal Aid Urbanized Area, ir
may not fully encotnpass-thenon-attam^
subdmsxons, states should identif^r a "VMT Tracking Area" forpurposes of VMT forecasting and
ireiCiCiii^. , _ ._-__'- . . _.-'-, _. _
13
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The boundaries of the VMT Tracking Area should be consistent with those of the several
CO inventories required.of CO non-attainment areas to the extent that VMT in the areas can be
logically related. In addition, the boundaries generally should be not smaller than the FAUA that
contains or overlays the designated non-attainment area since HPMS produces a statistically valid
sample only for the FAUA as a whole. However, a Tracking Area smaller than the FAUA may be
appropriate if it encompasses all vehicle travel contributing to the non-attainment situation and if the
state or another designated entity operates -a VMT tracking system equivalent in performance to
HPMS for that area The VMT Tracking Area need not exceed the Limits,of the MSA (unless
adjacent areas are involved in the non-attainment area).
The MSA itself may be the most convenient choice for the VMT Tracking Area. The
estimated VMT would, in that case, include the VMT within the FAUA, estimated directly from
HPMS, plus the VMT in the remainder of the VMT Tracking Area, estimated by a method selected
by the state after consultation with the lead planning agency for the area.
3.2 Highway Performance Monitoring System
All states containing a Moderate and/or Serious CO non-attainment area with a design value
greater than 12.7 ppm at the time of classification should estimate actual annual VMT using the
Department of Transportation, Federal Highway Administration's Highway Performance
Monitoring System, according to guidance listed in Section 2.1. Actual annual VMT should be
derived from estimates of VMT on all functional systems within the corresponding Federal Aid
Urbanized Area.8
All states, except for the states of California, Connecticut, Florida, Hawaii, Maine,
Michigan, Missouri, North Carolina, New York, Ohio, Oregon, South Carolina and Washington,
should base their 1990 estimates of actual annual VMT on unique sample panels for each Federal
8 States may obtain prior approval from the EPA Regional Administrator to supplement the 1990 HPMS counts
with counts not submitted to HPMS, if the collection of those individual non-HPMS counts equals or exceeds in
reliability the specifications for such counts listed in the the Department of Transportation's publications, as
described in Section 2.1.
14
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Aid Urbanized Area within the state, since sampling has already occurred at that level of
geographic detail.9
The excepted states have three options:
1. An excepted state may allocate its-state-wide HPMS estimate of 1990 VMT in all Federal
Aid Urbanized Areas to the given Federal Aid Urbanized Area on the basis of the
population aged 16 years and older within the associated Federal Aid UrbanizedArea in
comparison to the population aged 16 years and older within all Federal Aid Urbanized
Areas within the state. This allocation should be done separately for rural, small urban,
and urban areas.
2. An excepted state may also request approval from the EPA Regional Administrator to
supplement any available 1990 HPMS counts for the affected area with sufficient non-
HPMS counts to allow ah area-specific VMT estimate. Non-HPMS counts should be used
only if the collection of those individual counts equals or exceeds in reliability the
specifications for such counts listed in the the Department of Transportation's publications,
as described krSection 2.1.
3. Finally, an excepted state may use a method of its own choosing, provided the method is
well documented and justified in the SIP, to estimate 1990 VMT in each urban area on the
basis of the area-wide VMT submitted to the FHWA under HPMS.10
All states subject to the VMT forecasting/tracking provision should base their 1993 and
later calendar year's estimates of actual annual VMT on separate Federal Aid Urbanized Area
sampling. All counts used in-tfae VMT estimates should also be submitted as HPMS counts, so
that they meet the'HPMS quality^assurance guidance and are subjert to FlfW^A review.
9 The states of California, Honda, Hawaii, Maine, Michigan, Missouri, North Carolina, Oregon, South Carolina
and Washington base HPMS VMT estimates on one or more collective sample panels while the states of
Connecticut, New York and Ohio base HPMS VMT estimates on a combination of individual and collective sample
panels.
10 These estimates are considered by FHWA to be of less uniformly certain reUability than the area-specific
estimates from states that complete full HPMS ground counts in each urban area, but in individual cases they may
be of equal reUability depending on the method used by the state. '
15
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Tliree additional options for estimating 1990 VMT in unusual circumstances are described
below in the sections titled "HPMS-Like Alternative," "Areas Using Network-Based Models to
Estimate 1990," and "YMT Estimates for Localized Non-Attainment Problem."
3.3 Local Functional System VMT Estimates
While HPMS includes state-provided estimates of VMT on the local functional system,
these estimates are not generally based on current ground counts at statistically representative sites.
Instead the estimates are based on a method chosen by the state in light of its own circumstances.
States may continue to use the same methodology to estimate actual 1990,1993,1994 and 1995
VMT on the local functional system within the VMT Tracking Area.11
If, after a state submits its VMT forecast and attainment demonstration, it wishes to change
the methodology it uses to estimate actual VMT on the local functional system within the Federal
AM Urbanized Area, it should re-estimate, or re-forecast, as appropriate, 1990,1993, 1994, and
1995 VMT on that system using the same alternative methodology for each year.
Proper estimation of actual travel on the local functional system is most important for areas
subject to the highest ambient CO concentrations but will require some lead time. Therefore, states
containing areas designated as Serious CO non-attainment areas at the time of classification should,
by June 30,1994, propose to and obtain approval from the EPA Regional Administrator for a
method to estimate VMT on the local functional system within the Federal Aid Urbanized Area by a
count-based methodology equivalent to that described in Section 2.1, to take effect no later than
January 1, 1995. The EPA Regional Administrator will consult with FHWA when considering the
proposed count-based methodology.
. States may use any reasonable methodology to estimate 1990,1993,1994, and 1995 VMT
on the separate functional systems within the VMT Tracking Area but outside of the associated
Federal Aid Urbanized Area.
11 A state may substitute, for the 1990 estimate of actual VMT accumulated on the local functional system, a
methodology superior to that used in the past, provided that the substitution is reflected in both its VMT forecast and
its attainment demonstration.
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If, after a state submits its VMT forecast and attainment demonstration, it wishes to change
the methodology it uses to estimate actual VMT on the separate functional systems within the VMT
Tracking Area but outside of the associated Federal Aid Urbanized Area, the same procedures
apply as given above for changes in the method used to estimate VMT on the local functional
system within the FAUA.
As with count-based estimates of travel on the local functional system within the FAUA,
EPA believes that accurate estimates of VMT outside of the FAUA are necessary in those areas
subject to the highest CO concentrations. Therefore, states containing areas designated as Serious
GO non-attainment areas at the time of classification should, by June 30,1994, propose to and
obtain approval from the EPA Regional Administrator for a method to estimate VMT on the
separate functional systems within the VMT Tracking Area but outside of the associated Federal
Aid Urbanized Area by a count-based methodology equivalent to that described in Section 2.1, to
take effect no later than January 1,1995. The EPARegional Administrator will consult with
FHWA when considering the proposed count-based methodology.
3-5 HPMS-Like Alternative
Under certain conditions, a state may use an alternative to HPMS to estimate actual VMT.
If a state or other entity operates an HPMS-like system to track VMT within an area that
encompasses all vehicle travel contributing to the non-attainment situation and this alternative
system is equivalent to HPMS in terms of providing a reliable and accurate VMT estimate for the
area and if it conforms to Federal Highway Administration guidance, the state can use this
alternative system to estimate actual VMT. In order for this method to be used, adequate data for
making forecasts for this area should also be available. (See Section 4.3, "Historical Area-Wide
VMT Method,"below). TheTarea and the alternative system should be well documented and
justified in the SIP, and the SIPshouM demonstrate that the conditions of this paragraph have been
met. In this case, the area covered by the alternative system would be the VMT Tracking Area.
3-6 Areas Using Network-Based Models to Estimate 1990 VMT
Since 1990 ground counts submitted to HPMS may not be as comprehensive as ground
counts submitted for 1993 and later and since it may be possible for network-based travel demand
models to be validated for 1990, this guidance allows for the use of travel demand models to
estimate 1990 VMT under certain circumstances.
. 17
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An affected area with a strong network-based travel demand model that is based on
reasonably recent demographic trip-making data may use its model to estimate 1990 VMT after
consultation with EPA-and under the following conditions:
1. Urban areas within the state were not sampled separately under HPMS in 1990;
2. The state cannot supplement the available HPMS data with non-HPMS counts;
3. The model is validated with 1990 counts;
4. The model uses demographic inputs properly updated to 1990.
An area using this method should make sure that all VMT in the entire VMT Tracking Area
is included in the estimate. Most network-based models normally do not account for infra-zonal
trips or trips on functional classes outside of the modeling area. States may use any reasonable
method to estimate VMT on those functional classes that are within the VMT Tracking Area but that
are not included in the model.
3.7 VMT Estimation for Localized Non-Attainment Problem
If a state containing a Moderate CO non-attainment area covered under this guidance
receives prior approval for an attainment demonstration that addresses only locally generated
vehicle emissions in a finite number of specific intersections or other localized areas of high CO
concentrations (such that virtually all trips in each area originate or terminate outside it), the state,
with prior approval from the EPA Regional Administrator, may estimate and track the traffic across
the boundaries of each of the specified areas, rather than VMT over a wider area. Monitoring
should include all approaches to the area, meet FHWA guidance, and occur during the CO season
on those days of the week and times of day when CO exceedances occur. Base-year counts should
be taken within the 1987-92 period and should be adjusted for area-wide growth to 1990.
4.0 VMT FORECASTING FOR 1992 SIP SUBMTTTAL
4.1 Forecasting Years
By November 15,1992, affected states must forecast VMT in the VMT Tracking Area, for
1993 and each subsequent year until the year in which the SIP forecasts the primary National
Ambient Air Quality Standard for carbon monoxide will be attained.
18
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Since Moderate non-attainment areas must attain the primary National Ambient Air Quality
Standard for carbon monoxide by December 31,1995, an affected state must, by November 15,
1992, forecast 1993,1994, and 1995 VMT unless the SIP demonstrates that the area will reach
attainment prior to 1995, in which case the state only needs to forecast VMT through the year of
attainment. '
Since Serious non-attainment areas must attain the primary National Ambient Air Quality
Standard for carbon monoxide by December 31, 2000, a state containing an area designated as a
Serious non-attainment area at the time of classification must, by November 15,1992, forecast
1993,1994,1995,1996,1997,1998,1999, and 2000 VMT, unless the SIP demonstrates that the
area will reach attainment prior to 2000, in which case no forecast is required for years after the
attainment date.
4.2 Network-Based Travel Demand Modeling Process Methodology
The network-based travel demand modeling process brings together an area's highway and
transit network, demographic information, land-use forecasts, and trip characteristics to project
travel volumes and patterns. An area is represented by zones of activity, which are further defined
and connected by links of the roadway system. Through a series of steps, including trip
generation, trip distribution, mode choice, and trip assignment, the travel demand modeling
process allocates travel on the network.
Due to the range of inputs used, the travel demand modeling process provides more
complete information from which to determine VMT than other forecasting methods. Network-
based travel demand forecasting models are available for use on microcomputers.
It is not necessary for regional transportation models to treatthe transit network in as
sophisticated a manner as the highway network is treated in all cities for purposes of accounting for
.'"'' . . - .' &M» «" ' : .- . ' ' ' ' ~ - ~
the effect of transit on regiorrwide VMT. There are alternative approaches that can be used to
estimate the effects of transit travel on regionwide VMT. In most areas these alternatives can be
employed at significantly lower cost without sacrificing accuracy.
Where local planners do not envision a significant systemwide change in the transit
network through investment in new transit infrastructure or a significant increase in highway
congestion that would make transit more attractive as an alternative, transit travel may usually be
taken into account simply by subtracting flat percentages of Central Business District (CBD)-bound
and non-CBD-bound trips prior to traffic assignment. Reasonable adjustments in these flat
19
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percentages will account for the effect on transit ridership of TCMs other than major transit system
changes. Appropriate logit-based or elasticity techniques for making these minor adjustments
exist.
All states containing a Serious CO non-attainment area should forecast VMT by applying
growth factors based on a validated network-based travel demand modeling process to the 1990
actual annual VMT estimate derived by the methodology described in Section 3.0, "1990 VMT
Estimation and VMT Tracking."
All states containing a Moderate CO non-attainment area with a design value greater than
12.7 ppm at the time of classification should forecast VMT in the non-attainment area by this same
method, if such a model is currently available or if such a model could be made available in time to
allow the required SIP revisions and submissions.
States using the Network Travel Demand Model method should forecast VMT for the travel
demand model domain, based on equation (1).
(1) Forecasted VMT(futurei) = Actual VMT(1990) (Travel Demand Model VMT(futurei) /
Travel Demand Model VMT(i990))
where i = 1993, 1994, or 1995-2000
Since travel demand model output will be unavailable for some of the required VMT
forecasting years because the state will not have prepared separate demographic, land-use, and
transportation system projections for all years, the state should linearly interpolate between
chronologically adjacent travel demand model scenario years to calculate the values of both "Travel
Demand Model VMT(1990)» ^d "Travel Demand Model VMT(futtire.)" used in equation (1).
States using a network-based modeling process to forecast VMT growth should validate
their models against 1985 or more recent ground counts. In addition, the models should use a
constrained equilibrium approach to allocating trips among links; no link should be loaded beyond
its reasonable capacity; a distinction should be made between peak versus off-peak travel demand
and travel times; zone-to-zone travel times should be recycled as inputs until a self-consistent
equilibrium trip assignment among zones is achieved; and, if transit trips make up a significant
portion of historical or anticipated future travel on the network, zone-to-zone highway and transit
travel times should be recycled as inputs until a self-consistent equilibrium trip assignment is
20
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achieved among moctes as well. The demographic land-use assumptions for future years may be
judgmental b^rshould be reasonable in light of the planned highway and transit network, local
land-use poiicyV|rid other relevant influences on public and private development and location
'
States usjng a network-based model to forecastVMT growth should construct demographic
land-use scenarios for enough future years so that there is not more than five years between a year
for which a YMT forecast is required and the nearest base year or future year scenario. In
addition, the last scenario year for which land-use and other assumptions are made should be no
earlier m^
!985 ground counts should develop future land-use, employment, and other demographic
forecasts for at least 1995 and 2005, in order to forecast VMT fot 1993 through 2000.
c ^A
foreeak VMT b^^ for travel within the area and road types covered by the
modeled network and to use any other reasonable method to develop growth factors for VMT on
the local functional Astern excluded ffoirr the network model and in the remainder of the VMT
i-Tracking Arear T^
proposing a method to the EPA Regional ^ Adnwiistrator, who will consult with FHWA when
considering approyaL v -
state;in its/SIP adopts new of strengttiens existing transportation control measures
^^ change
Js based on sound
., K.-i, -- "^^^^'^^usbsS^6--**'-^ --"fr-^^""^- -
" -"-,' : ~-' -"T^?.^3lS,^^^-*-:*=is£sfca-».>. ii^Wfr-T^iX;":'''-;-1.
--" = ^»-.." ,-._ -.-^!%_:^TiW-*?sr~ **3i^Su.r*s«!«**»'-«.'-- --/-v =j>*r" '-r,.V;
1 area, in consultation with appropriate other
state and local organi^iom^^
unavailable and that such a model cannot be made available in time to allow the required SIP
revisions and^submissions,then the state may submit a request to the EPA Regional Administrator
for anEPA cornrratrhent to propose approval of a SIP based on historical area-wide VMT. The
EPA Regional^^Adrninistr^orwjU review the request in consultation with the Federal Highway
AdrninisttatibriRegiOTial QfGc? said will attempt to respond to the request within 30 days.
21 ,
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xtrapolation of tha, state's 1985-,990 HPMS repons for
Urbanized Area, according to equation (2).
where i = 1993, 1994, or 1995
State may use any reasonable methodology to forecast VMT on the separate functional
systems withtn the VMT Tracking Area but outside of the associated Federa. L
emissions in a finite «,*. of localized
traffic across the boundaries of each of the specified areas should abo base ft*
grow* factors derived torn an ordinary ieas, squares .inea, regression e^trapo
00. es,^ across these same boundaries, OT so other re,iab,e indicaTof tj g
thatpenod,iftrafficcountswerenotconducted. "iicgrowtni
Affected states that Back actual VMT using an HPMS-Iike alternative for a VMT Tracking
*e
. nrstortcal data from fte Amative cou«ir,g program to forecast grown,, if data were
-»«. "85.1990 period. If no, the SBK should justify some other forec«ing LL
being reliable, or forego use of the alternative HPMS-like method. g method
«
as
n
-ta w
effect ve after 1990 but pnor to a forecast year, it may adjust the
^^^xd^^^-
measures . based on sound anaJytica, techniques and is clearly documented in the
4.4
Safety Margjn
^"'^"^'^"cetelikelihoodofala.erfindingthatacraalannualVMTisgreater
sted annual VMT, that s^te may explicMy identify a safety margin for the non-
area forecasted VMT, provided fta, 4. state also bases its SIP emission inventory and
22
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attaininent demonstration on both the same higher level of VMT and the associated lower level of
vehicle speeds pa the ejected highway network.
5.0 REVISING A FORECAST
5.1 Network-Based Travel Demand Modeling Process Methodology T:
A state forecasting VMT using a network-based travel demand modeUng process should
annually revise itsforecast of VMTby applying equation (1), substituting for "AcnialVMTf^go)"
and "Travel Etemand Model VMT(i990)" the actual and model-forecasted VMT in the year prior to
the year the annual report is requued for u^ Federal Aid Urbanked Area. " ' - r;
Astate may, as part of its revised forecast, update its network-based traveldemandrnqdel
with new demographic and other input data and new base and forecast years, provided that the
state supplies all of the information described m Section 7.4, "Report dontent,"''ifertheupdated
model. The future highway an^triEnsit network for such a revised model is defir^W the current
highway network plus the modifications of that network on wWch tte^^
demonstration is based, unless the future network^ was modified since SIP approval by a
conforming transportation plan and transportation improvement program^ in which case die future
network is that modified network?The state may include a safety margin in its reyised^^^^^
5.2 , Highway Performance Monitoring System ;-.--''":; V.1^ '/V"^;'^-"-.
: _-.- : 'J-...'-""'T'-'? T-''-" - "-'-'_ ~ ^?-':^ ^ 1vJ'^'^^^':'^-.i^--^""^-5'l^S^:^^L,if;^,^7V-^' " ' . ' . -:': .- p ' " ..-"-":
-,.- -.'-_ ';'.-""-'%-'' :-''"~-r^-' '-.*' ^:-. ;;-^^7^""' ^H- -.^-_-'- ,;T^;f:s;;-r^v^.7^^r^«^:V" ""^;;:. "-;.;' * '. ,-"':.' '. L \:y-^^
_ ^^
Vt^pftipa^^ 1992 historical datiat
Urbaruzed Area boundaries that have been re-defined during the six-year period may
reasonable method to make adjustments to the re-defined geographic base. - £
States may use any reasonable methodology to re-forecast VMT on the separate functiorial
systems within the VMT Tracking Area but outside of die associated FederkAid^jrfjanized Area,
subject to the provisions of Section 3.3, "Local Functional System VMT Estimates^1 and Section
3.4, "VMT Estimates Outside of the Federal Aid Urbanized Area." The statemayjlftclude a safety
margin in its revised forecast. 3 ; :f
23
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6.0 CONTINGENCY MEASURES
By November 15,1992, a state containing a Moderate and/or a Serious CO non-attainment
area with a design value greater than 12.7 ppm at the time of classification must commit in its SIP
to implement specific measures if any estimate of VMT traveled in the area or a subsequent VMT
forecast exceeds the number predicted in the most recent prior forecast or if the area fails to attain
the CO National Ambient Air Quality Standard. These measures shall be included in the plan
revision as contingency measures to take effect without further action by the State or the
Administrator if the prior forecast has been exceeded by an updated forecast or estimate of actual
VMT or if the primary national standard is not attained by the applicable attainment date. This is a
statutory requkement. The statute does not further describe or specify the contingency measures
that must be adopted.
The provision that contingency measures be triggered whenever a new forecast exceeds an
old forecast, even if the actual VMT has not yet exceeded any forecast, appears to be intended to
address as early as possible any situation in which a trend towards higher than expected VMT has
been detected, since such a trend may affect the forecasted attainment date.
The need to preserve the integrity of the attainment demonstration and to react to
unexpected VMT growth must be balanced against the desirability of preventing a false trigger of
the contingency measures caused by the uncertainty in the VMT estimation and re-forecasting
processes. This uncertainty can result in a merely transitory appearance in one year that actual or
newly re-forecasted VMT exceeds the original VMT forecast, with the situation reversing in the
next year or the year thereafter.
The sampling and non-sampling error inherent in HPMS points to a practical and theoretical
need for a margin of error around VMT estimates and forecasts so that contingencies are not
triggered for small and possibly random deviations from forecasted VMT. At the same time, actual
annual VMT cannot be allowed to creep above the original attainment-producing forecast without
limit. Though successively higher forecasts may remain within the established margin of error
compared to the previous forecasts, they could, in fact, be drifting further and further from the
original forecast.
In order for a margin of error to serve the purpose of preventing a false trigger of
contingency measures without allowing unchecked VMT growth, actual annual VMT and later
forecasts should never be allowed to be more than the defined margin above the forecast that is the
24
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basis for an approved attainment demonstration. The use of an attainment-producing forecast as
the base for measuring deviations ensures that growth in VMT remains consistent with the
attainment demonstration, except for a de minimis deviation, or, if it does not, that contingency
measures are triggered.
Consequently, as previously explained in Section 2.3, contingency measures will be
triggered in any case where an estimate of actual annual VMT or an updated VMT forecast exceeds
the most recent prior VMT forecast by more than 5.0 percent in 1994,4.0 percent in 1995, and 3.0
percent thereafter. Contingency measures will also be triggered even though the margin of error is
less than the specified percentage for that year if, cumulatively, estimates of actual VMT or VMT
forecasts exceed the VMT forecast relied upon in the attainment demonstration for the area by more
than 5.0 percent.
As explained in Section 4.4, a state has the option of adding a safety margin to its VMT
forecasts for purposes of both the annual reporting requirement and its attainment demonstration, if
it wants to reduce the likelihood that actual annual VMT or a later forecast will exceed an earlier
forecast and trigger contingency measures.
This guidance does not identify the required contingency measures or the process for their
implementation. _ ,
7.0 ANNUAL REPORTING PROCEDURES
AH states containing Moderate and/or Serious CO non-attainment areas with design values
greater than 12.7 ppm at the time of classification must submit to the EPA Regional Administrator
annual updates of the annual VMT forecasts along with annual reports regarding the extent to
which such forecasts proved to be accurate. These reports shall contain estimates of actual vehicle
miles traveled in each year for which the forecast was required. These reports should be submitted
to EPA by September 30 of the year following the year for which the VMT estimate is made.
In accordance with Section 187(d)(l), states containing Serious CO non-attainment areas
also must submit by March 31, 1996 a demonstration that emission reductions achieved by
December 31, 1995 were as expected in the SIP. Data to estimate actual 1995 VMT may not be
available this early, in which case the most recent forecast of 1995 VMT may be used.
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7.2 Responsibility
The state should, in its SIP, identify the organization responsible for submitting these
reports by the required due date.
7.3 Process
Pursuant to Section 121, the state must, in its SIP, also provide for consultation among all
affected agencies, including, but not limited to, the state department of transportation, local
metropolitan planning organizations, the state department of environment (or the equivalent), local
air agencies, and local councils of governments.
7.4 Report Content
7.4.1 General Content
Each annual report should provide a comprehensive history of VMT forecasts and estimates
of actual VMT. For example, the report due on September 30,1994 by a state containing a
Moderate non-attainment area should contain the estimate of actual 1993 VMT. That report should
also contain the original 1993,1994, and 1995 VMT forecasts as well as updated forecasts of 1994
and 1995 VMT. The report should further show both the comparison of the estimate of actual
1993 VMT and the previously forecasted 1993 VMT and the comparison of the previously
forecasted 1994 and 1995 VMT submitted by November 15,1992 and the revised forecasts of
1994 and 1995 VMT. The next annual report would repeat this information and add the 1994
actual VMT and the updated forecast of 1995 VMT.
Changes in urbanized area boundaries based on the 1990 census and improvements to
HPMS over time should be explained and accounted for in the annual reports but will not alter the
annual report requirement itself. For example, an expanded FAUA would mean that the state
continues to use HPMS to estimate VMT in the FAUA, but only a smaller non-FAUA area requires
VMT estimates using the state selected method.
7-4.2 Highway Performance Monitoring System-1990 Base and Tracking VMT
All states containing Moderate and/or Serious CO non-attainment areas with design values
greater than 12.7 ppm at the time of classification should document within the required annual
reports the following information:
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a. Statistical Precision12
(i) Actual ground counts for each HPMS sample segment, the date(s) those counts
were completed and the number of hours over which those counts were made.
(ii) Actual number of ground count sample segments required to achieve the FHWA-
prescribed confidence intervals for each HPMS facility class/volume group estimate
of average daily traffic volume.
(iii) For each HPMS facility class/volume group, the actual number of HPMS sample
segments counted.
b. Adjustments and Expansions13
(i) The number of road miles within the Federal Aid Urbanized Area by facility
class/volume group.
(ii) The facility class/volume group factors) used to expand the HPMS segment data
into Federal Aid Urbanized Area VMT estimates.
(iii) The methods, data sources, and specific factors used to adjust counts on sample
segments for month, day-of-week and/or hour-of-day.
(iv) The methods and specific factors used to adjust counts on sample segments for
those segments not actually counted in a given year.
c. VMT Accumulated on Each Volume Group Within Each Functional System Except the
Local Functional System
The resulting estimates of annual^yMT accumulated on each volume group
within each functional system, except the local functional system, within the
Federal Aid Urbanized Area.
12 Alternatively, the report may reference other specific reports, internal agency records, and/or FHWA data bases
for this information.
13
Ibid.
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d. VMT Accumulated on the Local Functional System
The specific methodology and calculations14 used to estimate VMT
accumulated on the local functional system within the Federal Aid
Urbanized Area.
e. VMT Accumulated Outside of the Federal Aid Urbanized Area
The specific methodology and calculations15 used to estimate VMT
accumulated on functional systems within the VMT. Tracking Area but
outside of the associated Federal Aid Urbanized Area.
7-4.3 Network-Based Travel Demand Modeling Process Methodology
All states using a network-based travel demand modeling process under Section 4.2 should
document the following information within the SIP, and subsequent changes should be
documented in the required annual reports.
a. Model Accuracy and Confidence
(i) . That the travel demand forecasting model used is validated with 1985 or more
recent calendar year ground counts according to generally accepted modeling
procedures;
(ii) The methods and measures used to validate the model and the results of that
validation;
(iii) The extent to which the traffic assignment matched the base year ground count for
groups of links ranked by average daily traffic volume;
(iv) That the travel demand forecasting model method uses a constrained equilibrium
approach to allocating trips among links;
14 Calculations may be referenced.
15 Ibid.
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(v) That a distinction is made between peak versus off-peak trip volumes and travel
times;
(vi) That model outputs on zone-to-zone travel times are recycled as inputs until a self-
consistent equilibrium trip assignment among zones is achieved and that this
recycling is done until a self-consistent equilibrium trip assignment is achieved
among modes as well, if transit trips make up a significant portion of historical or
expected future travel on the network;
(vii) That no link is loaded beyond its reasonable capacity;
(viii) That the travel demand forecasting model forecasts of future year VMT are based
upon the future demographic and land-use assumptions of the agency responsible
for making such forecasts for transportation planning purposes and upon the future
highway and transit network, and that the demographic land^use assumptions for
future years are reasonable in light of the planned highway and transit network,
local land-use policy, and other relevant influences on public and private
development and location decisions.
(ix) That the highway and transit network assumptions are consistent with the
attainment strategy and demonstration through the attainment date, and (if a model
scenario year falls after the attainment date) that beyond the attainment date the
network assumptions are based on reasonable expectations,
b. "Model Definition and Inputs
(i) Geographic Domain
The geographic domain to which all of the model inputs and VMT forecasts refer.
(ii) Socio-Economic Data16 *
Socio-economic data associated with each year for which VMT is forecasted,
including, but not limited to, the following:
16 Alternatively, the report may reference other specific reports, internal agency records, and/or FHWA data bases
for this information.
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c.
(A) Population;
(B) .Number of households;
(C) Employment.
(iii) Network
A general description of the network and a reference to complete documentation of
network parameters.
Model Outputs17
(i) Trip Distribution Output
Person-trip lengths in minutes by trip purpose.
(ii) Trip Generation Output
(A) Person trips by purpose for internal trips;
(B) External-internal vehicle trips;
(C) External-external vehicle trips.
(iii) Mode Split
(A) Transit person-trips;
.**
(B) Auto person-trips; ...
(C) Auto driver person-trips.
17
Ibid.
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(iv) Traffic Assignment
(A) The constrained equilibrium speed versus volume-to-capacity equations
used by functional class;
(B) Average speed;
(C) VMT by functional class;
(D) VMT by geographic area; e.g., ring/sector;
d. Growth in VMT Accumulated on the Local Functional System
The specific methodology and calculations18 used to forecast growth in
VMT accumulated on the local functional system within the Federal Aid
Urbanized Area.
e. Growth in VMT Accumulated Outside of the Geographic Domain of the Network But
Within the Federal Aid Urbanized Area
The specific methodology and calculations19 used to forecast growth in
VMT accumulated on functional systems within the associated Federal Aid
Urbanized Area but outside of the geographic domain of the network-based
travel demand modeling process. .
f. Growth in VMT Accumulated Outside of the Federal Aid Urbanized Area
The specie methc^ology and calculations20 vised to forecast growth in
VMTaccumulated on functional systems within the VMT Tracking Area but
outside of the associated Federal Aid Urbanized Area. «**
18 Calculations may be fefereoced.
19 Ibid.
20 Ibid. .
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7.4.4 Highway Performance Monitoring Svstem-Based Forecasts
a. Historical Data and Regression Equation
For all states that are permitted, under Section 4.3, "Historical Area-Wide
VMT." to use the Highway Performance Monitoring System to forecast
Federal Aid Urbanized Area VMT in the VMT Tracking Area, the historical
data and regression equation used to forecast that VMT.
b. VMT Accumulated on the Local Functional System
The specific methodology and calculations21 used to forecast VMT
accumulated on the local functional system within the Federal Aid
Urbanized Area.
c. VMT Accumulated Outside of the Federal Aid Urbanized Area
The specific methodology and calculations22 used to forecast VMT
accumulated on functional systems within the VMT Tracking Area but
outside of the associated Federal Aid Urbanized Area.
7.4.5 Record Keeping Requirements
Each state containing a Moderate or a Serious CO non-attainment area with a design value
greater than 12.7 ppm at the time of classification should commit in its SIP to keeping all
information supporting the annual reports referred to in this section for three years arid should
commit in its SIP to allowing EPA staftand/or private persons under contract to EPA to audit that
- fUrf
supporting information. This audit will be conducted in consultation with FHWA.
21 Ibid.
22 Ibid.
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8.0
AREAS RECEIVING EXTENSIONS UNDER SECTION 186(a)(4)
The CAAAspecify that, upon application by any state, the Administrator may extend for
one additional year the attainment deadline provided that the state has complied with all
requirements ar^^mmitmentsi^a^
more than one exceedance of the National Ambient Air Quality Standard for carbon monoxide has
occurred in the areain the year preceding the extension year. ;
No more than two one-year extensions may be issued for a single
non-attainment area.
Under this guidance, all of the
Reporting Procedures," apply during the extension period.
reporting requirements specified in Section 7.0, "Annual
9.0 RECLASSIHCATION OF MODERATE AREAS UPON FAILURE TO ATTAIN
According to Section 180(b)(2X^
carbon monoxide Moderate non-attainment area, the Administrator will determine, based on a
Moderate area* design value as of me attainment date, whether that area has attained the primary
National Ambient Air Quality Standard for carbon monoxide by that date. Any Moderate area that
the Administrator finds has not attained the standard by that date will be ^classified as a Serious
area ' - -.....- - ---..'---'
area.
^Moderate
unlessaaextensionimbeengraMedbytheEPAAdministrator. If the first one-year extension has been 'granted the
appfica^
attainment date is December 31,1997.
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10.0 INVENTORIES
10.1 Guidance Applicable to Specific Non-Attainment Area Inventories
10.1.1 1990 Inventory
All states containing Moderate and/or Serious CO non-attainment areas with design values
greater than 12.7 ppm at the time of classification should use the annual VMT estimates developed
in accordance with Section 2.1, "Actual Annual Vehicle Miles Traveled," as the starting point for
the 1990 inventory [187(a)(l)].
10.1.2
"Periodic Inventories" F187(aK5)1
All states containing Moderate and/or Serious CO non-attainment areas with design values
%
greater than 12.7 ppm at the time of classification should use the annual VMT estimates developed
in accordance with Section 2.1, "Actual Annual Vehicle Miles Traveled," as the starting point for
the "Periodic Inventories" [187(a)(5)].
10.1.3
"Specific Annual Emission Reductions" ri87(a)(7Yl
All states containing Moderate and/or Serious CO non-attainment areas with design values
greater than 12.7 ppm at the time of classification should use the annual VMT forecasts developed
in accordance with Section 4.0, "VMT Forecasting for 1992 SIP Submittal," as the starting point
for.the "Specific Annual Emission Reductions" [187(a)(7)] inventory.
10.1.4
Attainment Demonstration Inventory
All states containing Moderate and/or Serious CO non-attainment areas with design values
greater than 12,7 ppm at the time of classification should use the annual VMT forecasts developed
in accordance with Section 4.0, "VMT Forecasting for 1992 SIP Submittal," as the starting point
for the Attainment Demonstration inventory.
10.1.5
Severe Area Milestone T187(d)( 1 )1
All states containing Serious CO non-attainment areas should use the annual VMT forecasts
developed in accordance with Section 4.0. "VMT Forecasting for 1992 SEP Submittal," as the
starting point for the Severe Area Milestone [187(d)(D] inventory.
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10.2 Guidance Applicable to All Inventories in CO Non-Attainment Areas with Design Values
.Greaterthan 12.7ppm ~ '*- ~
The follpwjng guidance applies to all of the emission inventories listed in Subsection 10.1
above./ ":. : ' -;.-_- '-. --:;-_ ; .-- _ _- - * ."..'" - """ . "".":";" :'':':::- ...- "..,.'
1. CO emissions estimates generally are the product of a VMT estimate and an emission factor
that depends upon the average speed at which that VMT occurred. Since CO emission factors are
not linear with speed, total CO emissions should be estimated making use of the available
information regarding the distribution of VMT among roadways of different speeds and other
characteristics that effect mobile source eniission factors. AU non-attainment area emission
inventories should at a minimum be derived from a breakdown of total historical or forecasted
VMT into functional system-specific VMT estimates (or a similar disaggregation of VMT among
road and/or geographic categories). Forecasted total VMT, excluding that on die local functional
system, should be disaggregated into functional system-specific VMT in the same proportion as the
most recent HPMS-derived estimates of VMT by system, unless a validated network-based travel
demand model is used toforecast VMT,in which case forecasted total VMT shpuMb^7;-
disaggregated as indicated by the model. Travel demand models that do not meet the performance
and validation requirements for use in. forecasting VMT growth may nevertheless be suitable for
deriving speed estimates. Emission factors applied to the VMT on each functional system or
roadway should reflect the estimated speeds for that system or roadway by peak and off-peak trip
-volumes.. , '.--.._ . -. :.-: A-,,.-;:-T;..: ;'v -.^.''" ' : '" ;;; .- '-./"- -.:,-.":-."', ;'.,-.:-., V.1-
2. ~.= ~';,rvMT estimates preparedunofer t^ guidanc»are for annual^^V^
' .._;_-.. i-:*--:'i;/;;i :4.t.''p,'''r??.* ?-;:% '-' .r*",^ ;F;;"j ",-**'«. -" %^--^^,z^^£.^^~s---~j-~~"-^.zL-r,-'-- ~ ";.t . ' ir'~--f:,"' '?'., "» ,' -^--L "-.^jf~~'m * -^W-.'.- v1.*^-^ -..- .;-^.-',^: -.;;~- " > <
- * -- l~^tT%-
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11.0 AUTHORITY
Authority for this guidance is granted to EPA by Section 187(a)(2)(A), "Vehicle Miles
Traveled," of the Clean Air Act Amendments of 1990.
12.0 TIMELINE
The following table provides information and dates relevant to CAAA requirements for CO
non-attainment areas.
January-March, 1992
Draft base year CO inventories submitted.
November 15,1992
The first forecast of VMT for each year before the attainment year is due from
states with CO non-attainment areas that have design values greater than 12.7
ppm. Subsequent yearly forecasts and reports are due on September 30. (For
Serious CO areas, the report due in 1996 should be submitted by March 31,
1996.)
SIPs from states with Moderate and/or Serious CO non-attainment areas that
have design values greater than 12.7 ppnti must contain contingency measures
to take effect if the prior VMT forecast has been exceeded by an updated
forecast or estimate of actual VMT or if the primary national standard is not
attained by the attainment deadline.
CO non-attainment areas with a design value of 9.5 ppm or above are required
to mandate that fuel sold during the period of high CO concentrations contain
2.7 percent oxygen by weight.
January 1, 1993
A state with Moderate and/or Serious CO non-attainment area that has a
design value greater than 12.7 ppm should begin sampling each HPMS
facility class/volume group separately for each non-attainment area, as stated
in its SIP.
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May 15, 1994
Deadline for CO non-attainment areas with a 1980 population of 250,000 or
more and a design value of 16,0 ppm or greater to provide for a clean-fuel
vehicle fleet program. , .. ^
June 30, 1994
Deadline for states with Serious CO non-attainment areas to obtain approval
from the appropriate EPA Regional Office for a count-based method to
estimate VMT on separate functional systems within the VMT Tracking Area
but outside of the Federal Aid Urbanized Area. The approved method is to
take effect by January 1,1995.
Deadline for states with Serious CO non-attainment areas to obtain approval
from the appropriate EPA Regional Office for a count-based method to
estimate VMT onihe local functional system within the Federal Aid Urbanized
Area. The approved method is to take effect by January 1,1995.
September 30,1995
First periodic inventory is due. Subsequent inventories are due every three
years thereafter until attainment.
December 31,1995
Moderate CO non-attainment areas are required to attain the National Ambient
Air Quality Standard for CO.
March 31,1996
Serious CO non-attainment areas must submit a demonstration that the
emission reduction specified in the 1992 SIP revision has occurred by
December 31,1995.
If the specified reduction has not occurred, a SIP revision with economic
incentives and a transportation control measures program is due within nine
months of failure to make the demonstration or of EPA's notification of an
inadequate demonstration.
December 31,2000
Serious CO non-attainment areas are required to attain the National Ambient
Air Quality Standard for CO.
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