Guidance for On-Road Testing
Requirements for Enhanced Vehicle
Inspection and Maintenance (I/M)
Programs
United Stales
Environmental Prutuclion
Agency

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Guidance for On-Road Testing
Requirements for Enhanced Vehicle
Inspection and Maintenance (I/M)
Programs
Transportation and Climate Division
Office of Transportation and Air Quality
U.S. Environmental Protection Agency
SEFA
United States
Environmttntsl ProlGfiliOn
Ag en cy
EPA-420-B-20-020
March 2020

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1. Purpose of Guidance
This guidance was developed to clarify how the on-road testing requirement can be met in states with
mandatory enhanced vehicle emission inspection and maintenance (I/M) programs. On-road testing is a
necessary element of an I/M program that is required by the Clean Air Act (CAA) to be operated at the
enhanced performance level. On-road testing involves the collection of emissions data from a sample of
subject in-use vehicles within an enhanced I/M program. The analysis of data obtained from on-road
testing can be useful in assessing the effectiveness of an I/M program.
In support of efforts to increase compliance, the Environmental Protection Agency (EPA) developed this
guidance to help state and local governments meet their CAA and regulatory requirements in enhanced
I/M program areas. This guidance also provides options and reflects the latest technologies and practices
in use by enhanced I/M programs across the United States. Finally, this guidance was written as a result
of a 2018 audit by the Office of Inspector General (OIG) regarding EPA oversight of enhanced I/M
programs, entitled, Collecting Additional Performance Data from States Could Help EPA Better Assess
the Effectiveness of Vehicle Inspection and Maintenance Programs (OPE-F Y17-0018).1
2.	What are the Clean Air Act requirements?
The 1990 Amendments to the CAA required I/M programs for certain areas across the country based
upon various criteria, such as air quality status, population, and/or geographic location. The CAA
established two performance levels of I/M programs: "basic" I/M for ozone nonattainment areas
classified as moderate, and "enhanced" I/M. Pursuant to CAA sections 182, 184 and 187, enhanced I/M
programs are mandated in the following areas:
•	All serious or worse ozone nonattainment areas that had a 1980 urban population of 200,000 or
more;
•	Metropolitan statistical areas with a 1990 population of 100,000 or more in the Ozone Transport
Region (regardless of their air quality classification); and
•	All moderate or worse CO nonattainment areas with a design value greater than 12.7 parts per
million (ppm) at the time of classification that had a 1980 urban population of 200,000 or more.
One of the obligations of an enhanced I/M program is to perform on-road testing of in-use vehicles for a
small percentage of the area's fleet of motor vehicles. Among other things, section 182(c)(3)(B)(i)
authorizes EPA to establish "a performance standard achievable by a program combining emission
testing, including on-road emission testing..." Additionally, for enhanced I/M areas, section
182(c)(3)(C)(i) requires these state programs to include "on-road testing devices" as a necessary element.
3.	What are the on-road testing regulations for enhanced I/M areas?
In 1992, EPA promulgated the original I/M rule at 40 CFR 51 Subpart S, and EPA has since amended
the rule several times. The I/M rule establishes the technical, procedural and administrative requirements
to be met by basic and enhanced I/M programs. The following paragraphs provide additional
information from the current I/M rule's on-road testing requirements.
1 This report was released on September 25, 2018 and can be found at: www.epa.gov/office-inspector-general/report-
collecting-additional-performance-data-states-would-help-epa-better.
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Specifically, 40 CFR 51.351(b) establishes on-road testing as part of the enhanced I/M performance
standard. The complete set of provisions detailing on-road testing is found in 40 CFR 51.371. This
section includes the following:
On-road testing is defined as testing of vehicles for conditions impacting the emission ofHC, CO,
NOx and/or CO2 emissions on any road or roadside in the nonattainment area or the I/M
program area. On-road testing is required in enhanced I/M areas and is an option for basic I/M
areas.
(a) General requirements:
(1)	On-road testing is to be part of the emission testing system, but is to be a complement to
testing otherwise required.
(2)	On-road testing is not required in every season or on every vehicle but shall evaluate the
emission performance of 0.5% of the subject fleet statewide or 20,000 vehicles, whichever is
less, per inspection cycle.
Note that section 51.371(a)(2) of the I/M rule establishes the volume of cars to be tested in an on-road
testing program, with each enhanced I/M program area being required to evaluate the emission
performance of at least 0.5% of that area's subject fleet (or 20,000 vehicles, whichever is less) within the
corresponding inspection period.2 For example, if an enhanced I/M area has 1 million vehicles that are
subject to I/M testing on a biennial basis, then the state shall conduct on-road testing to at least 5,000
vehicles over the course of a two-year period.
Section 51.371(a)(3) and (4) describe additional requirements for on-road testing programs including the
type of testing and compliance:
(3)	The on-road testing program shall provide information about the performance of in-use
vehicles, by measuring on-road emissions through the use of remote sensing devices or by
assessing vehicle emission performance through roadside pullovers including tailpipe or
evaporative emission testing or a check of the onboard diagnostic (OBD) system for vehicles so
equipped. The program shall collect, analyze and report on-road testing data.3
(4)	Owners of vehicles that have previously been through the normal periodic inspection and
passed the final retest andfound to be high emitters shall be notified that the vehicles are
required to pass an out-of-cycle follow-up inspection; notification may be by mailing in the case
of remote sensing on-road testing or through immediate notification if roadside pullovers are
used.
2	The inspection cycle corresponds to the testing frequency of that particular I/M program. The test frequency is how often a
subject vehicle in that I/M program area needs to be tested to comply. The performance standards for I/M programs assume
an annual test frequency but another test frequency schedule (such as biennial) may be approved for I/M programs if the
required emission targets of the I/M program are achieved. See 40 CFR 51.3 5 5 (a).
3	When first promulgated in 1992, the I/M rule indicated that the on-road testing requirement must be met by using remote
sensing devices or by conducting road-side pull-over, tailpipe testing (57 FR 52950 (Nov. 5, 1992)). However, with the
advent of OBD systems, the nature of vehicle I/M testing has changed from predominantly tailpipe testing to analysis of the
OBD system. In July 2000, EPA revised the I/M rule to provide additional regulatory options in conducting on-road testing
(65 FR 45526 (July 24, 2000)).
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Because of the options that states have in designing the on-road testing program for each enhanced I/M
area, the provisions of section 51.371(b) obligate the state to outline in their state implementation plan
(SIP) how their chosen on-road testing program complies. The SIP for each enhanced I/M program area
shall describe the on-road testing program, including the types of testing, test limits and criteria, the
number of vehicles to be tested, the methods for collecting, analyzing, utilizing, and reporting the results
of on-road testing as well as budget, personnel and legal authority for the program.
Lastly, section 51.371(b)(3) allows for additional emission reduction credits, over and above those
projected for other aspects of an I/M program, to be granted for on-road testing programs that require
out-of-cycle repairs for high-emitting vehicles identified through the on-road testing program.
4. What OIG recommendation is addressed by this guidance?
The OIG report included a finding that EPA lacked required performance data to assess the effectiveness
of some state enhanced I/M programs partly due to inconsistent compliance with on-road testing
requirements. As a result, the OIG highlighted that further improvements in mandatory on-road testing
compliance were necessary:
When states do not conduct program evaluations and on-road testing, they are failing to meet
applicable statutory and regulatory inspection and maintenance requirements. This means that
the EPA and states lack complete program performance data to determine whether the program
is achieving projected emission reductions. They also do not have a complete picture of the
overall performance of the programs in question.4
The OIG audit made several recommendations to EPA's Office of Air and Radiation (OAR) for assuring
consistent and effective implementation of enhanced I/M programs. The complete list of the OIG's
recommendations may be found in Appendix A of the OIG report. Recommendation #4 of the OIG's
2018 report addressed mandatory on-road testing in enhanced I/M areas, and OAR responded that
guidance would be issued:
Recommendation 4: Verify whether states are performing mandatory on-road testing or
determine the reason why they are not and offer assistance to obtain compliance.
Response 4: OAR agrees with this recommendation and will respond by directing EPA 's Office
of Transportation and Air Quality (OTAQ) to issue guidance that clarifies that on-road testing is
required by the Clean Air Act (CAA) for all mandatory, enhanced I/M programs, that testing
using Remote Sensing Devices (RSD) meets the definition of on-road testing, and that using RSD
to perform program evaluation testing can be used to meet both the Act's on-road testing
requirement for enhanced I/M areas as well as the biennial program evaluation requirement for
enhanced I/M programs. OTAQ will also ask the EPA Regional Offices (RO) to provide the status
of applicable states performing mandatory on-road testing, to determine the reason(s) for any
problems, and to identify technical assistance as needed to obtain compliance.5
4	Collecting Additional Performance Data from States Could Help EPA Better Assess the Effectiveness of Vehicle Inspection
and Maintenance Programs (OPE-FY17-0018), pg. 14.
5	Ibid. pg. 25.
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To satisfy this recommendation, OTAQ worked closely with the EPA Regional Offices to determine the
status of enhanced I/M areas satisfying the on-road testing requirement as well as issue this guidance for
meeting the requirements in enhanced I/M areas.
5. What methods are available to satisfy the on-road testing requirement?
This section will briefly describe the various options for compliance with the statutory and regulatory
requirements for on-road testing in enhanced I/M programs.6
a.	Remote Sensing Device (RSD) Programs
RSD provides a snapshot of emission rates from a large quantity of vehicles as they are driven on
roadways. RSD installations generally are units set up on the side of a roadway with a light (or laser)
source and detector, placed either at the side of or above a roadway. RSD units send infrared or ultra
violet beams through vehicle exhaust plumes and then use optical sensors to analyze the emissions for a
fraction of a second as vehicles pass by the unit. RSD units record speed and acceleration which are
measured at the same time as the emissions measurement, providing information about the engine load.
Also, a camera captures an image of the vehicle's license plate to identify the vehicle through registration
databases.
b.	Roadside Pullovers
Roadside pullovers are another means of conducting on-road testing of in-use vehicles in enhanced I/M
areas. Just as the name implies, in roadside pullovers, the state air agency in association with a
corresponding law enforcement agency stops and tests vehicles alongside the road in the enhanced I/M
program area. Roadside pullovers can be random, targeted or a combination of both. One example of
why targeted pullovers may be employed by states is to obtain a better sample size of older vehicles with
greater high-emitting potential. Older vehicles are a much smaller portion of the subject I/M fleet and
without targeted sampling, may be under-represented in an on-road testing program.
EPA's I/M website contains an example roadside inspection program report to be used as a resource for
states wishing to conduct their own roadside inspections of subject in-use vehicles.7 Because, these on-
road testing roadside pullover options mirror similar test procedures conducted at the I/M program area's
inspection stations (except that these on-road tests are performed in the field using portable or mobile
equipment), more information on specific test procedure details may be found in the I/M rule. Roadside
pullovers can be conducted using one or more of the following methods:
o Onboard Diagnostic (OBD) System Check - All model year 1996 and later light-duty
vehicles and light-duty trucks are equipped with certified OBD systems. This roadside
pullover test option is performed in the same manner as an in-station OBD I/M test. First, a
visual Malfunction Indicator Lamp (MIL) bulb test is conducted with an ignition key cycle
6	As mentioned in Section 4 of this guidance, OAR's response to Recommendation #4 notes that data collected from on-road
testing can be used in conjunction with the enhanced I/M area's biennial program performance evaluation as outlined in CAA
section 182(c)(3)(C) and detailed in regulation at 40 CFR 51.353(c). OTAQ is developing additional guidance on biennial
program evaluations.
7	See https://www.epa.gov/sites/production/files/2016-06/documents/roadside.pdf.
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(i.e., key-on/engine off). Then an OBD data acquisition device is connected to the OBD
system's data link port (or vehicle connector) to evaluate the OBD system's readiness, MIL
status as well as any diagnostic trouble codes (DTC) that are commanding the MIL on. More
details on OBD test procedures may be found at 40 CFR 85.2222 Onboard diagnostic test
procedures.
o Tailpipe Testing - In this type of on-road testing, the state agency responsible for roadside
pullovers of subject vehicles employs a gas analyzer to test the vehicles either at idle or, in
combination with a portable (trailer-based) dynamometer, under load. Roadside tailpipe
testing evaluations have historically been based on either Two-Speed Idle (TSI) or Steady-
State testing such as Acceleration Simulation Mode8 (ASM). However, it is not clear how
prevalent these types of tests are at this time especially for OBD-equipped vehicles which can
be covered by other options in this guidance. TSI and Steady-State test procedures may be
found in Appendix B of 40 CFR 51 Subpart S.
o Evaporative Emissions (System and/or Gas Cap Pressure) Test - Using mobile or portable
test equipment, a state or law enforcement agent conducts an evaporative system integrity test
during the roadside pullover using the procedure outlined in 40 CFR 51.357 Test procedures
and standards.
In addition, any of these roadside pullover options can be combined with visual/anti-tampering
inspections. Although visual/anti-tampering inspections do not satisfy the on-road testing requirement
by themselves, they provide a beneficial complement to roadside pullovers. During a pullover, a law
enforcement or state agent who is trained or certified as an inspector-mechanic can conduct a visual anti-
tampering inspection as verification of the vehicle's required emission control components. Visual
emission control device checks shall be performed through direct observation or through indirect
observation using a mirror, video camera or other visual aid. These inspections include a determination
as to whether each applicable device is present and appears to be properly connected and of correct type
for the certified vehicle configuration.
c. Remote OBD
Data collected from a Remote OBD program can also be used to satisfy the on-road testing requirement.
The verification of the emission systems of OBD-equipped in-use vehicles can be achieved remotely,
without a roadside pullover or visit to an inspection station. Remote OBD is the collection of OBD
parameters via telematics (e.g., via the cellular phone data network), and this approach can provide
additional convenience and flexibility to the motorist and the I/M Program operator. With remote OBD,
an electronic device or 'dongle' is connected to an OBD system's data link port. The device reports the
vehicle's OBD system status while being driven.
Remote OBD can be continuous, periodic or episodic. That is, the dongle can stay connected to the
vehicle all the time, for a certain period of time, or just long enough for the OBD system to become
8 See www.epa.gov/state-and-local-transportation/veliicle-emissions-inspection-and-maintenance-im-policY-guidance-
and#ASM.
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"ready" and report the OBD system's status. For example, one state has partnered with telematic
providers as well as with private business locations such as gas stations, car washes, oil change shops,
and repair service centers, to create a device-sharing distribution network. Once a remote OBD test has
concluded, a motorist, at his/her convenience, can return the device to one of these locations for re-use.
In addition, many vehicles already have the appropriate self-reporting telematic equipment onboard.
Owners of these vehicles have the option of activating a subscription-based, in-vehicle, maintenance
communications service. With these services, the motorist can request that the OBD system data be
reported to the appropriate state agency. Similarly, many fleet operators already use Remote OBD to
monitor their vehicles for logistic and maintenance purposes.
6.	Who can I contact for more information on this guidance?
For questions concerning a particular state or I/M program area, contact the I/M coordinator at your EPA
Regional Office. A listing of Regional Mobile Source Contacts is available at:
www.epa.gov/transportation-air-pollution-and-climate-change/office-transportation-and-air-qualitv-
contacts-topic.
General questions about this guidance can be directed to Joe Winkelmann at EPA's Office of
Transportation and Air Quality at: winkelmann.ioseph@epa.gov.
Additional information regarding I/M programs can be found on EPA's website: www, epa.gov/state-
and-local-transportation/vehicle-emissions-inspection-and-maintenance.
Another good resource for I/M programs is the EPA-supported National OBD Clearinghouse:
www.obdclearinghouse.com/.
7.	Does this guidance create any new requirements?
No, this guidance is based on CAA requirements, existing associated regulations, and does not create any
new requirements. The CAA and EPA's I/M rule at 40 CFR Part 51, Subpart S contain legally binding
requirements. This document is not a substitute for those provisions or regulations, nor is it a regulation
itself. Thus, it does not impose legally binding requirements on EPA, states, or the regulated
community, and may not apply to a particular situation based upon the circumstances. EPA retains the
discretion to consider and adopt approaches on a case-by-case basis that may differ from this guidance
but still comply with the statute and applicable regulations. This guidance may be revised periodically
without an opportunity for public comment.
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