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4
Emerging Emissions Testing
Technologies
New technologies continue to be developed to provide faster, more convenient,
end more accurate emissions testing. Since inspection end maintenance (~/M)
programs have been in operation for approximately 30 years, the accumulated
data can be used for motor vehicle profiling. In addition, on-board diagnostics
(OBD) systems and remote-sensing technologies may eliminate traditional I/M
testing for some vehicles. These emerging emissions technologies are de-
scnbed below.
MOTOR VEHICLE PROFILING
Motor vehicle profiling can be used to help determine whether a vehicle
is likely to be a high emitter. By examining past emissions performance of a
vehicle (through existing T/M records), as well as performance for similar
makes and models, the likelihood of whether a vehicle will pass or fail an I/M
inspection may be determined. There are two types of profile:
~ Low-emitter profile (LEP:The LEP attempts to assign a probability
that a vehicle or group of vehicles will pass an I/M test. It relies on I/M re-
cords indicating which vehicle makes, models, and model years have low
incidences of T/M failure.
90
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Emerging Emissions Testing Technologies 91
· High-emitter profile (HEP)—The high-emitter profile similarly at-
tempts to predict the probability that a vehicle or group of vehicles will fait an
EM test. Examples ofthis type of profiling are provided by Wenzel and Ross
(] 996), who used California remote-sensing data, and Wenze! (! 999a), who
used Arizona IM240 data to identify vehicle makes and models with high
malfunction rates. However, data from random roadside surveys in California
have shown significant differences between the HEP and on-road data.
These profiles might be used to make I/M programs more cost-effective
by targeting more frequent inspection to those vehicles most likely to need
repair and exempting from testing vehicles with a small likelihood of high emis-
sions. For example, depending on the state, many programs exempt vehicles
2-5 model years old (MECA ~ 999~. The developers of one LEP estimated
that such a "clean screening" model could screen out at least 50% of the
vehicles from testing with little impact on emissions benefits (Klausmeier and
Kishan 1998~.
The California Bureau of Automotive Repair uses a HEP in their en-
hanced I/M program to help determine whether to send vehicles to test-only
facilities, which are thought to perform more accurate tests. Eastern Research
Group developed and maintains the computer program for performing this
analysis (Eastern Research Group ~ 997~. This HEP uses the prior inspection
history of a vehicle; historical failure rates of vehicles ofthe same year, make,
and model; and remote-sensing measurements ofthe vehicle. The California
I/M Review Committee (IMRC 2000) reported the failure rates and initial
emissions test results for HEP versus non-HEP vehicles. As shown in Table
4- I, the HEP made only a small improvement in identifying vehicles likely to
fail, and the improvement was only for post-1986 model-year vehicles. The
benefits of the HEP model are much smaller than those estimated by Klaus-
meier and Kishan ~ ~ 998) from a small sample of data from California. How-
ever, updating the profile for recent test data might improve its performance.
If a HEP is used in I/M program design, it is important to consider the
regressive impacts that will occur to low-income motorists who may be more
frequently targeted for testing. To the extent such a policy is regressive, it
could be combined with the most cost-effective supporting policies, such as
repair assistance or scrappage programs, in an attempt to mitigate its negative
effects.
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92 Evaluating Vehicle Emissions I/M Programs
TABLE 4-l Results of the HEP Used in the California Smog Check
Program
HEP Directed Random Directed Not Directed
Failure Rate 26% 22% 23%
Initial emissions
HC (ppm) 71 63 68
CO (%) 0.45 0.41 0.46
NOX (ppm) 520 485 494
Note: Vehicles could be directed using the HEP, randomly directed, or not directed to
a test-only facility, but directed to a test and repair facility.
Source: IMRC 2000.
ON-BOARD DIAGNOSTICS
The use of OBD technologies in I/M programs represents a major shift
from current practice. As described in Chapter 2, the OBDIT system on ~ 996
end newer vehicles uses sensors to monitor end modify the performance ofthe
engine and emissions control components. Itis possible to identify problems
with OBD sensors or emissions control components by interfacing a diagnostic
analyzer ("scan tool") with the vehicle ' s electronic processor to download any
diagnostic trouble codes. These codes identity emissions-control systems and
components that are malfunctioning. If the OBD I/M program is operating
properly, OBDIT inspections will fail vehicles if either the vehicle's emissions-
con~o} components are, or have been, malfunctioning or if the sensors monitor-
ing emissions-control components are malfunctioning. This program is in con-
trast to a traditional I/M emissions-testing program where a vehicle is in-
spectedto determine if itis emitting, et the time of its appearance et the testing
station, more pollutants than a standard set by individual states. The U.S.
Environmental Protection Agency (EPA 200 ~ ~ has recently finalized an OBD
rule that requires states to begin implementing OBD testing in I/M programs
for ~ 996 and newer OBD-equipped vehicles.
The OBDII system does not actually measure emissions. Because this
system does not measure emissions but rather alerts drivers that there is a
problem that might result in excess emissions, evaluating the benefits from
such a system is not straightforward. Direct emissions reductions from the
repairs resulting from an OBDIT alert cannot be estimated without subjecting
the vehicle to at least two tests that measure emissions, one before and one
after the repair. In addition, the objective of OBD is to prevent vehicles from
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Emerging Emissions Testing Technologies 93
becoming high emitters. It is difficult to quantify the emissions benefits of
preventing vehicles from becoming high emitters.
An important aspect of the OBD system is that it is required to maintain
a memory of past events, and store a history of previous problems, even
though the problem no longer exists. Thus, a vehicle in an OBD I/M program
might fait due to an intermittent problem. Another aspect of the OBD I/M
system is that it might fait a vehicle due to a failed sensor. Though the infor-
mation collected by the sensor might be used to minimize emissions, the on-
board computer on OBDTI-equipped vehicles can use an alternate strategy to
control vehicle emissions until the failed sensor is repaired or replaced. The
emissions using the alternate "fail-safe" strategy can be almost as low as if the
control system was using the primary sensor. Thus, some repairs, particularly
repairs to sensors, will result in little, if any, immediate emissions reductions.
This can make OBD-directed repairs look ineffective in the short term.
As descnbed in several studies below, the design of the OBDII system
means that the malfunction indicator light (MIL or "check engine" light) will
illuminate and diagnostic trouble codes issued for a potentially significant num-
ber of vehicles despite vehicle emissions being below the state's I/M emissions
cutpoints and even the vehicle's certification standards. Furthermore,
OBDIT's strict malfunction criterion (the MTE illuminates if a problem is de-
tected that could cause emissions to exceed ~ .5 times the vehicle's emissions
certification standards) were not set by individual states to meet their air-qual-
ity needs, but were set nationally according to the needs of areas with the most
stringent requirements for vehicle emissions control.
If people respond to the MIL and the OBD system operates properly,
there is little need for aperiodic inspection. Vehicles wiliremainatIowemis-
sions levels throughout their lifetimes. However, there is a question as to
whether drivers will seek repairs as the vehicle ages, and runs out of warranty.
As described in several studies below, there is also the concern over the large
number of vehicles with high emissions and no MID illuminated.
There are a number of issues related to the OBD I/M programs that will
first be highlighted. They are
· Readiness codes before and after repairs.
· Failure criteria.
· Emissions or pollutants of concern.
· Fast pass using OBDIl.
· Human response to the MTL.
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94 Evaluating Vehicle Emissions I/Al Programs
We discuss each in more detail below. In addition, we also discuss recent
regulations and results of studies related to the use of OBD in I/M.
Readiness Code
Through the use of various sensors, the OBDIT system tests the compo-
nents of the emissions-control and fuel-management systems to ensure that
they are operating correctly. There is a specific criterion for each emissions-
control system component that must be met before an OBDIT system sensor
is considered ready, meaning the component in question has been monitored.
These criteria are defined and implemented by each manufacturer. Forexam-
ple, certain components are monitored as soon as the engine is fumed on, after
as many as 40 engine restarts, or only after the vehicle is driven under a cer-
tain Toad and speed. In the case of monitoring the evaporative emissions-
contro} system, readiness codes are not set until the vehicle is exposed to cer-
tain ambient temperatures.
A significant part ofthe problem is that the detection limits are set to very
sensitive levels. If, for instance, the system was just to detect if the gas cap
was in place, the test could be completed almost on every trip. Because the
intent ofthe evaporative control system monitoring is to reliably detect a very
small leak (e.g., a I-millimeter diameter hole), the conditions necessary to
make such a determination might not occur very often and perhaps never in
the normal use of a certain vehicle. If the OBD detection limits were set at
higher levels, the tests could be completed more often.
EPA's OBD rule (EPA 2001) requires that all but two ofthese readiness
codes be set to indicate that a particular emissions control component has been
monitored by the OBDIT system. If more then two readiness codes are found
unset, then the vehicle would be tested by an emissions tailpipe test or rejected
from OBD testing. EPA (2000c, 200 ~ ~ estimates that the frequency of finding
more than two readiness codes unset will be small. However, McCTintock
(2000a) found in Colorado a much higher level of readiness codes being unset
than the EP A ' s e s tim ate s .
The readiness codes are turned off when the battery is disconnected,
possibly occurring as the result of repairs. If that occurs, they must be reset
before the vehicle can be subjected to another OBD check. Resetting might
be an issue for motorists attempting to retest their vehicles immediately after
repairs. Additionally, if it is easier to pass an emissions tailpipe test than an
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Emerging Emissions Testing Technologies 95
OBDIT check and the tailpipe test is an option for vehicles with unset readiness
codes, motorists that fear failing an OBDIT check may attempt to avoid this
test by simply disconnecting the battery. The current OBDIT system has no
"stay-alive" memory that can persist through a battery disconnection. Future
OBD systems might have such memory components and carry records of
vehicle identification number, odometer reading, and a record ofthe MILs and
their source and date. This information might provide a solution to the issue
of unset readiness codes.
Failure Criteria
Most I/M programs fail vehicles for excess emissions that are much higher
than vehicles certification standards. The OBDIT system, by design, illumi-
nates the MIL (and fails a vehicle) if a problem is detected that might cause
emissions to exceed 1.5 times the certification standard. In addition, MIL
illumination occurs if the system determines that a monitor or sensor is not
responding properly, even without increased emissions.
Emissions or Pollutants of Concern
Many state I/M programs are designed to address a particular air-quaTity
problem. Colorado's program is designed to control carbon monoxide (CO).
The nonattainment areas in Texas are concerned about controlling nitrogen
oxides (NOx). Several states are concerned about hydrocarbons (HC) orNOx,
while others are concerned about both HC and NOx, but one to a greater
degree than the other. I/M cutpoints and standards are designed to control the
emissions or pollutants of concern for each state. However, an OBDII pro-
gramwill fad] a vehicle if any ofthe emissions (HC, CO, end NOx) exceed the
failure criteria.
Fast Pass Using OBDI!
States may consider using the OBDIT system as a fast-pass test. This
means that vehicles that demonstrate a clean OBDII system will be passed
and not subjected to an emissions test. If the MIL is illuminated or there are
unset readiness codes, the vehicle will not fail, but the vehicle owner will be
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96 Evaluating Vehicle Emissions I/M Programs
given information for suggested repairs, and the vehicle will be required to
undergo an emissions test. Under the current regulation (EPA 2001) the fast-
pass test may be used only in the start-up of an OBDTI test and for one cycle
of vehicle inspection requirement. The fast-pass test could also be used for
areas that are not required to implement an I/M program but are considering
an OBDIl test as a preventive control measure.
Human Response to OBDIl
The intent ofthe MTE is to inform motorists that they need to check their
emissions control systems because there is an indication of some malfunction.
However, many motorists are unlikely to spend the time and money to bring
vehicles in for repair voluntarily, especially if the vehicle's emissions systems
are outside the warranty period and the vehicle's operation is not affected.
This might become especially problematic as the vehicle ages. Warranty
periods -for most components are relatively short compared with current vehi-
cle lifetimes. The federal emissions control warranty is 96 months/80,000
miles for major emissions control components (such as the catalyst), and 24
months/24,000 miles for other components (such as sensors, PCV valve, EGR
valve). Auto manufacturers have extended these warranties to 3 years/36,000
miles and 10 years/100,000 miles.
If motorists are required to have the OBD system checked as part of an
I/M test, as with any I/M testing system, there is the possibility of cheating to
avoid test and repair. We discussed above the possibility that motorists will
simply disconnectbatteries, causing unset reediness codes, which would allow
them to take a more lenient IM240 tailpipe test rather than an OBD test.
Other avoidance methods might also arise, although it is too early to determine
how serious or widespread this problem could be.
Perhaps the most serious problem with motorist response to the MIL is the
confusion that is likely to occur about what an illuminated check-engine light
represents and what its relationship is to emissions and the cost-effectiveness
of emissions reductions. Current studies, discussed later in this section, indi-
cate little consistency between a MIL illumination and the probability of an
IM240 failure. In addition, repairs of many vehicles withilluminatedMILs do
not produce substantial emission reductions, atleastin the short-run. In part,
it could be that many of the problems caught by OBDII are early-stage prob-
lems. Repairing these vehicles might result in much lower emissions later in
the vehicles' lifetimes. Failures could also be due to evaporative emissions
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Emerging Emissions Testing Technologies 97
problems. Even after repair ofthese problems, improvements are difficult to
measure. The inconsistencies between results of IM240 and OBD tests might
produce motorists' confusion and serious skepticism about OBD I/M pro-
grams.
Recent OBD I/M Regulations
EPA recently finalized a rule concerning the use of OBD in I/M (EPA
2001~. It mandates the introduction of OBD tests for cars equipped with
OBDIT (1996 model year and later) end provides states the flexibility to com-
pletely replace traditional I/M tests with OBD checks. ~ The rule also extends
the deadline by ~ year (untiT January I, 2002) for states to implement OBD
checks, and loosens some criteria for performing OBD inspections without all
readiness codes being set. It also allows the states to phase-in the OBD test.
Technical Analyses Regarding OBD I/M Tests
Table 4-2 contains a summary description of several recent studies regard-
ing OBDIl's use in I/M programs. Three EPA studies were summarized in
a draft technical support document (EPA 2000c) that accompanied the OBD
rule. The objectives of the EPA studies were to assess the effectiveness of
OBD I/M testing for exhaust and evaporative emissions and to investigate
implementation issues through the information collected from the Wisconsin
enhanced T/M test lanes.
The first study evaluated the effectiveness of OBD I/M for tailpipe testing.
EPA recruited 20 ~ OBDIl-equipped vehicles with either a malfEmction indica-
tor light (MIL) illuminated ~ ~ 94 vehicles) or no MIL illuminated but suspected
of having high emissions (eight vehicles).2 Once recruited, each vehicle was
iThe Clean Air Act Amendments of 1990 and later regulations mandated that OBD
checks be incorporated into I/M programs by January 1, 2001. However, until this
proposed rule, states would have had to implement OBD checks in addition to tradi-
tional I/M programs. EPA concluded that there is no reason to subject vehicles to
both IM240 and OBD checks (EPA 2000c).
2The discrepancy between the stated number of vehicles recruited (201) and the
total number of vehicles in these two categories (202) exists because one vehicle was
recruited twice for separate problems.
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98 Evaluating Vehicle Emissions I/M Programs
TABLE 4-2 Studies of OBD Issues Related to UM Programs
Vehicle
Study Recruitment
EPA study of Solicitation, mainly 193 vehicles
MIL illuminated from rental car
vehicles agencies
EPA study of I/M lanes 8 vehicles
high emissions,
no MIL vehicles
EPA Same, with in- 30 vehicles
evaporative duced evaporative
emissions study emission failures
Vehicles Tested Comments
Tailpipe comparison of
IM240 with OBDII for
vehicles with MIL on
(EPA 2000c)
Vehicles suspected of
high emissions with MIL
off (EPA 2000c)
Evaporative emissions
effectiveness of OBDII
(EPA 2000c)
CE-CERT Rental car fleet 75 vehicles Tailpipe comparison of
(University of and newspaper IM240 with OBDII MIL on
California, ads (Durbin et al.2001)
Riverside)
Wisconsin I/M lanes 116,667 1996- Tailpipe comparison of
1998 vehicles IM240 with OBDII MIL on
(EPA 2000c)
Colorado I/M lanes (fails 3,162 vehicles Tailpipe comparison of
CDPHE study back to back in 2000; 1,466 IM240 with MIL on,
IM240 fails and/or vehicles in 1999 including retest data
MIL on) (Barrett 2001 ~
Colorado I/M lanes (fails 21 vehicles (out Tailpipe comparison of
CDPHE study back to back of a study IM240 with OBDII MIL
IM240 fails and/or design of 100) on, including repairs
MIL on) up to April 2001 (Barrett 2001 ~
given a Federal Test Procedure (FTP) emissions test as well as a laboratory
IM240 emissions testy Table 4-3 shows that ofthe ~ 94 vehicles with the MIL
3The difference between a lane IM240 test, those conducted as part of an I/M
program, and a laboratory IM240 test is that the latter can control better for factors
such as the quality and calibration of the test equipment, ambient conditions, and tire
pressure.
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Emerging Emissions Testing Technologies 99
TABLE 4-3 Results of EPA Study of Tailpipe Emissions for Vehicles
with MIL Illuminated and Vehicles Suspected to Have High Emissions
FTP> 1x FTP> 1.5x
No. of MIL Self- Certification Certification
Vehicles Cleared Standards Standards
Vehicles with MIL illuminated 194
Vehicles with no MIL 8
illuminated but suspected to
have high emissions
Source: EPA 2000c.
11 58 31
~ 4
illuminated, ~ ~ had the MIL self-clea~A before any emissions tests were com-
pleted, and 58 had emissions greater then the certification standards. Ofthe
58 vehicles with emissions greater then the certification standards, only 3 ~ had
emissions greater than 1.5 times the certification standards.
Table 4-3 indicates that 70°/O of the vehicles ( l 3 6) had the MIL illuminated
but emissions below certification standards. Ofthese ~ 36 vehicles, 97 vehicles
were identified to have a broken part (EPA 2000c). The remaining vehicles
might have had an intermittent problem, but it no longer existed when the
vehicle was tested. The problem might have been the result of a loose gas
cap, a fuel-injector problem, or an intermittent electrical problem, or the vehicle
could have been driven under an extreme driving condition. The OBDII sys-
tem still stores much ofthis information in its memory and allows technicians
to review the pest history ofthe originalproblem. The large number offailing
vehicles with relatively Tow emissions was also noted by
Durbin et al. (200 ~ ~ in a study of 75 vehicles with MILs illuminated. That
study found that 63°/O of vehicles with MILs illuminated had emissions below
their certification standards, and 79°/O had emissions below 1.5 times their
certification standards.
The eight vehicles in Table 4-3 with no MIL illuminated were recruited
because of either high IM240 test lane results or other characteristics such as
high mileage or driveability problems that suggest high emissions. Of those
eight, four had emissions greater then ~ .5 times their certification standards for
4The MIL self-cleanng occurs when an intermittent problem is not detected on
later system scans by the OBD system and the MIL tutus off.
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~ 00 Evaluating Vehicle Emissions I/M Programs
CO anchor NOX on the FTP test but no MIL illuminated. The OBDIT catalyst
monitoring system verifies the efficiency for HC. Thus, if the vehicle had high
CO or NOx, and low HC, it would not trigger the MIL.
This study also identified 21 vehicles with FTP emissions greater then two
times their certification standards, and compared whether the OBD or labora-
tory IM240 test was better able to identify them. Of the 21,19 were correctly
identified by the OBD system, whereas only ~ 3 were correctly identified by
the laboratory IM240 test.
A second EPA study induced failures in the evaporative system on 30
vehicles to determine whether the OBD system could detect a range of such
failures. These included missing, loose, or leaking gas caps and disconnected
purge lines used to overload the carbon canister. Of these 30 vehicles, MTE
illumination occurred in over 80°/0 (25 vehicles). It should be noted that tradi-
tional I/M tests for evaporative emissions (the purge and pressure tests de-
scribed in Chapter 3) are difficult to perform. Thus, the results of this study
are encouraging in terms of the ability of OBD to identify problems in the
evaporative system.
The third EPA study used data gathered in Wisconsin to assess failure
rates and other issues associated with implementing an OBDI/M program.
This study examined the relative failure rates for OBDI/M versus lane IM240
testing. For 1996 model-yearvehicles, the OBD failure rate fromtheWiscon-
sin lane data was 2.4%, and the IM240 failure rate was 2.~%. However, the
percentage of vehicles that failed both was only 0.2%, which indicates that
only a small fraction (about ~ 0%) of vehicles failing one also failed the other.
Figure 4-l shows data for the number of vehicles failing IM240 and OBD tests
for model-year ~ 996- ~ 998 vehicles. The large discrepancies between TM240
and OBD test failures are obviously of major concern.
The Wisconsin study also estimated the average time to perform an OBD
I/M inspection (31 seconds) and identified atypical data link connector loca-
tions. The issue here is that the connector is placed out of sight and is difficult
to locate as one moves from mode} to model. The study also looked at OBD
readiness code data. Current regulations for OBD I/M testing require I/M
programs to reject a vehicle with two or more readiness codes unset. Readi-
ness codes were found unset in 5.~°/0 of 1996 model-year vehicles, 2.3% of
~ 997 model-year vehicles, and I.4% of ~ 998 model-year vehicles. The reason
for these lower "not ready" rates on newer vehicles could be due to manufac-
turers; building better OBD systems or to lower mileage accumulation on these
newer vehicles. Allowing states to proceed with OBD I/M testing with two
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Emerging Emissions Testing Technologies 107
Singer recommended that infrared analyzer results for HC should be multiplied
by a factor of about 2 (Singer et al. ~ 9984; the scaling factor may vary depend-
ing on the chemical composition ofthe HC emissions. Emissions tests, such
as the FTP and IM240 described above, use a flame ionization detector (FID)
to measure HC emissions. This detector is known to respond similarly to
alkalies, alkenes, and aromatics and thus is better suited for measuring the HC
mass present.
Nitrogen Oxides
NOX is defined as the sum of nitric oxide (NO) and nitrogen dioxide (N02),
although the direct emissions from internal combustion engines are dominated
by NO (Kirchstetter et al. ~ 996; Jimenez et al. 2000~. Remote-sensing capa-
bilities for NO have been developed more recently than those for CO and HC.
Measurements of NO emissions are challenging because of overlapping ab-
sorption by other exhaust constituents: water vapor in the infrared and aro-
matic HC in the ultraviolet (UV). Various approaches have been used, includ-
ing tunable infrared diode lasers (Nelson et al. ~ 998; limenez et al. ~ 999) and
UV spectroscopy (Zhang et al. ~ 996a; Popp et al. ~ 999b). By modifying the
UV absorption technique used in earlier DU remote sensors, Popp et al. were
able to achieve a lower detection limit (i.e., increased sensitivity) and eliminate
interference due to UV absorption by aromatic HC.
A limited comparison of NOX concentrations by remote sensing and on-
board measurements in heavy-duty diesel truck exhaust has been reported
(Jimenez et al. 2000~. Remote-sensing measurements of the NOX/CO2 ratio
agreed win similar measurements made on-board an instrumented diesel Suck,
although the authors note that remote-sensor accuracy was assessed over only
a limited portion ofthe likely range of NOX/CO2 emissions ratios. An instru-
ment comparison and further evaluation of remote-sensing methods for mea-
suring NOX emissions is needed. Remote-sensing site selection is especially
problematic for measuring NOX emissions accurately because oftheir depend-
ence on operating conditions, but it might not be critical for identifying high
NOX emitters.
Particulate Matter
Development ofcapabilities for remote sensing of particulate matter (PM)
emissions is an area of active research. The Coordinating Research Council
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~ 08 Evaluating Vehicle Emissions I/M Programs
is currently sponsoring a study to evaluate the effectiveness of remote sensing
to measure PM emissions from heavy-duty diesel vehicles (CRC Project E-
56~. Qualitative measurements of PM emissions using remote sensing will
likely be available soon. Quantitative measurement of mass emissions rates
for PM will be more difficult to achieve because the scattering and absorption
of light by airborne particles are complex functions of particle size and chemi-
cal composition.
Site Selection and Effects of Engine Load
An important consideration when measuring vehicle emissions by remote
sensing is careful selection of roadside monitoring sites. Sites where vehicles
might tee sampled during cold-start operation should tee avoided, because vehi-
cle emissions are higher than normal until the engine and emissions-control
systems have warmed up. Sites where driving conditions involve frequent
heavy acceleration and high-Ioad driving (e.g., accelerating on steep uphill
grades) might yield unrepresentative emissions results associated with opera-
tion in commanded enrichment modes. (Enrichment modes have lower air/fuel
ratios and increased CO and HC emissions.) To correct for effects of engine
Toad on exhaust emissions, the roadway grade at remote-sensing sites should
be noted, and the speed and acceleration of each vehicle passing by the remote
sensor should tee measured. This is now common practice, but information on
vehicle speed and acceleration is rarely available in older remote-sensing
studies.
Ashbaugh et al. (1992) and Zhang et al. (1993) noted that tailpipe HC
concentrations measured by remote sensing were elevated at a site where
vehicles were decelerating. The significance of this result is not that such
driving modes are an important source of HC (fue! consumption is Tow under
these conditions, hence mass emissions rates are also low), but rather that such
sites should be avoided in remote-sensing studies.
Jimenez (l 998) and McCTintock (l 998) developed more formal approaches
to estimating engine load based on readily observed vehicle-operating parame-
ters, such as speed and acceleration in addition to roadway grade. Vehicle-
specific power (VSP) is estimated as the sum of loads due to aerodynamic
drag (wind resistance), vehicle acceleration, rolling resistance (tire-roadway
friction), and hill climbing, divided by the mass ofthe vehicle and commonly
reported in kilowatts per metric ton. On a fleet-average basis, CO emissions
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Emerging Emissions Testing Technologies 109
appear to be less sensitive to engine load than other pollutants; they remain
fairly constant over a VSP range of -5 to 20 kilowatts per metric ton (kW/t)
(Bishop et al. ~ 999~. HC emissions decrease with increasing engine load, over
a VSP range of-15 to 15 kW/t (Bishop et al. 1999~. NOX emissions often
increase over the same VSP range, but further study of this relationship is
needed.
Coverage
it remote sensing is used to screen the vehicle fleet to help identify high-
emitting vehicles, a significant issue is the need to measure by remote sensing
the emissions from most of the vehicles operating in a given area. This need
might require multiple remote sensors, which must be moved to different road-
side sampling locations every few days. Current constraints, such as the need
to measure across a single lane oftraffic, make it difficult to achieve complete
coverage of the fleet. A remote-sensing study conducted by the Bureau of
Automotive Repair (Amlin 1995) using 10 remote-sensing vans in a 3-month
period was able to obtain CO emissions measurements matched to readable
license plates for 380,000 vehicles registered in Sacramento County, California.
Emissions from 58°/O ofthese vehicles were measured more than once in this
study. About 2 million remote-sensing measurements obtained at multiple
roadside sampling sites were needed to achieve a 47°/O level of coverage for
the ~ ~ 0,000 vehicles registered in Sacramento County. Improved coverage of
the vehicle fleet could have been obtained by increasing the number of sites
and days where remote sensors were operated; when the study ended, 30°/O
of vehicles driving by the remote sensors were being observed for the first
time. Note that remote sensors provided measurements for unregistered and
out-of-county vehicles operating within Sacramento County; some ofthese
vehicles would not be covered by traditional I/M programs.
Need for Quality Assurance and Quality Control
As with any emissions testing program, a critical element is data quality.
Success in using remote sensingin field studies has been mixed, with problems
often apparent when multiple remote-sensing instruments and measurement
teams are involved. Walsh and Gertler (1997) reviewed remote-sensing data
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~ ~ O Evaluating Vehicle Emissions I/M Programs
collected in Texas during ~ 996 in Houston, DalIas/Ft. Worth, and E! Paso. For
the most recent 10-15 vehicle model years, HC emissions measured by one of
the two remote sensors used in Houston were systematically lower by factors
of 2-3 than those measured with the other. They concluded that the most
probable cause was "related to calibration gases used by the individual instru-
ments during the field study." There was also evidence of systematic differ-
ences in CO measurements from Houston relative to those measured in
Dallas/Ft. Worth with different remote-sensing instruments. Walsh and
Gertler (1997) noted that although the study sponsor was aware ofthe utility
of a side-by-side comparison ofthe various remote-sensing units being used,
it was not done because of budget and time constraints.
The experience described above with remote sensing in Texas is not
unique: similar problems arose when multiple contractors and remote-sensing
instruments were used in field studies in Phoenix and Sacramento. In such
cases, there appears to have been too much emphasis on the number of vehi-
cles and sites sampled and insufficient time and effort devoted to quality con-
trol.
Use of Remote Sensing to Identify High Emitters
The question of whether remote sensing should be used to identify high
emitters in I/M programs has been controversial. Proponents of remote sens-
ing argue that current I/M programs waste time and money because about 20
vehicles have to be tested to identify one high emitter that is a candidate for
repair; some vehicles might be adjusted by their owners or technicians to pass
scheduled emissions tests, but they do not remain clean or are difficult to re-
pair; and motorists might register their vehicles in ways that avoid I/M require-
ments. Opponents argue that remote sensing is not a reliable way to measure
vehicle emissions, motorists might avoid known remote-sensor locations and/or
take steps to frustrate remote-sensing device measurements, and use of re-
mote sensing might lead to an unacceptably high rate of false failures, reducing
public acceptance of I/M programs.
Several valuable studies have been conducted in which both remote sens-
ing and standard I/M program tests have been used to measure emissions from
the same vehicles. The most useful comparisons are made with I/M program
tests administered at the roadside on vehicles pulled over immediately after
their emissions were measured by remote sensing. Some analysts emphasize
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Emerging Emissions Testing Technologies 111
perceived inadequacies in the correlation between remote sensing and I/M test
results for individual vehicles as a reason why remote sensing should not be
used in I/M programs. More appropriate categorical analyses focus on the
ability of remote sensing to identify high-emitting vehicles that will fait UM
program tests, as discussed below.
When comparing remote-sensing readings with roadside emissions inspec-
tion results, it is important to remember that the vehicle itself can be a signifi-
cant source of variability, especiallyin the case of intermittent malfunctions in
the emissions-control systems. Therefore, it is unrealistic to expect any emis-
sions test to be ~ 00°/0 repeatable in making pass-fai} determinations for individ-
ual vehicles, even for the same test administered repeatedly. For example,
Knepperet al. (l 993) measured emissions from TO "normal" and7 "high-emit-
ting" vehicles, all ~ 986 or later mode} years. Emissions were measured in the
laboratory using the FTP loaded-mode test described in Chapter 3. Knepper
found that relative to normal emitters, the high-emitting vehicles showedgreat-
er emissions of CO and HC and greater variability of emission rates within
each test vehicle. Variability in emission rates for the high-emitting vehicles
was traced to changes in air/fuel ratio from test to test.
Hawthorne (Los Angeles) 1989 Study
Lawson et al. ( 1990) describe a study in which vehicles were pulled over,
and roadside inspections made immediately after vehicle emissions had been
measured by remote sensing. Of 50 vehicles that were identified by remote
sensing as having high emissions (more than 2% CO in their exhaust), 28 failed
the CO portion ofthe roadside inspection and 15 failed for other reasons, for
a total of 43 failing vehicles out of 50. The rate of false failures (error of
commission) was 14%.
Of the ~ 5 vehicles in the remote-sensing/pullover study that failed the
roadside inspection for reasons other then high CO emissions, ~ werepre-1975
models that also would have failed for CO if a tailpipe concentration of less
than 2% had been required to pass. (The actual CO concentration required
to pass the roadside test ranged from 2.5% to 7°/O for pre-1975 vehicles, in
contrast to levels of approximately ~ % CO required for ~ 980 and newer cars.)
Of ~ 0 additional vehicles that were measured by remote sensing to have
Tow CO emissions, all passed the CO portion ofthe roadside inspection (2 of
these ~ O vehicles failed for reasons other than high CO emissions). The error
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~12 Evaluating Vehicle Emissions I/M Programs
of omission for this small sample of vehicles was 20%: remote sensing ofCO
emissions alone did not pick up other problems that leaf to failure ofthe road-
side inspection.
Rosemead Boulevard (Los Angeles) 1991 Study
A larger-scale combined remote-sensing/roadside inspection study was
performed during summer 1991 in El Monte, California, as described by
Stedman et al. ~ ~ 994~. Vehicles were identified as high emitters based on two
remote sensors both reading greater than 4% CO. There was a preference
for purling over post- 980 mode] vehicles for roadside inspections because of
the less stringent emissions requirements for older vehicles. Of 307 vehicles
that had both remote-sensor and roadside inspection data available, ~ 5°/0 failed
the exhaust emissions (idle test) portion of the roadside inspection, and the
overall failure rate (including vehicles with tampered or noncomplying
emissions-control systems identified during an underhood inspection) was 92%.
Michigan 1992 Study
Stephens et al. ~ ~ 995) assessed variability in vehicle emissions by examin-
ing correlations between multiple remote-censor readings of CO and HC emis-
sions and between remote-sensor and roadside IM240 emissions test results
for 170 vehicles. In general, the correlations between remote-sensor and
IM240 results improved as the number of remote-sensor measurements of a
vehicle's emissions increased from ~ to 4. This finding indicates that the rate
of false failures is likely to decrease when more than one high remote-sensing
reading is required to identify a vehicle as a high emitter. It is unclear, how-
ever, whether simply raising the cutpoint would be a more effective method for
identifying high emitters and reducing the number of false failures.
Orange County (Los Angeles) 1995 Study
Lawson et al. ( 1 996b) conducted a study in Orange County, California, in
1995, where high-emitting vehicles were identified by remote sensors and
pulled over for repairs. In that study, measurements from two remote sensors
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Emerging Emissions Testing Technologies 113
separated by 100-150 feet were used to identify high emitters, whose criteria
were average readings of 4°/O and 0. ~ °/O for CO and HC, respectively. During
a 10-day period, remote-sensing readings were obtained for 19,000 vehicles at
the two locations. Nearly ~ 0°/O of the vehicles transiting the remote-sensing
devices at the two sites exceeded the high-emitter cutpoint criteria, with a high
emitter passing the remote-sensing devices every 2. ~ minutes. More than 600
vehicles were pulled over for possible participation in the repair program, and
140 were selected for repairs and testing.
Once a car was chosen for participation in the program, it was given an
IM240 test on EPA's transportable dynamometer; in nearly all cases, the
TM240 test was given on the same day the vehicle was selected for program
participation. Once the vehicle was given the IM240 test, it was transported
to a repair garage where it was given the two-speed BAR90 idle tests and
visual Smog Checkinspection. In this unique data set, remote sensing, IM240,
and BAR90 data were available for the same vehicles, with emissions readings
taken on nearly the same day.
The average pre-repair IM240 emissions rates ofthe vehicles in this study
were 70, 6.2, and 2.0 g/mi for CO, HC, and NOX, respectively. Eighty-six
percept ofthe vehicles in the program failed the IM240 testusingEPA's 1997
standards for the IM240; 66%, 78°/O, and 27% failed for CO, HC, and NOX
(even though the vehicles were not stopped for NOX emissions), respectively.
Ninety-six percent of the vehicles that participated in the program failed the
BAR90 inspection. This percentage includes those that failed a functional test,
shown as an underhood failure in Figure 4-3. Of the five vehicles that passed
the BAR90 test, four failed the IM240. Seventy-three percent ofthe vehicles
in the program were classified as being "tampered" with or "arguably tam-
pered." Additional data on pass/faiT rates are shown in Figure 4-3. This study
showed that remote-sensing identifications of high CO- and/or HC-emitting
vehicles were confirmed in 86% to 96% of IM240 and BAR90 emissions tests
administered on the same or the next day.
Arizona High-Emitter Program
The state of Arizona implemented a remote-sensing program to identify
high-emitting vehicles in the Phoenix area, starting in ~ 995. The program was
terminated ~ years later by state legislators, because of problems including
costs in the final year of over $300 per high-emitting vehicle identified and
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114
100%
80%
60%
·~
40%
to
Ohio
Evaluating Vehicle Emissions I/M Programs
IM240 Test Result IM240 Test Result
(RSD C0>4%) (RSD HC>O. two)
~/~
BAR90 Idle Test BAR90 Idle Test
(RSD C0>4%) (RSO HC>O.1%)
~ Fail CO and HC · Fail CO only E3 Fail HC only E! Fail UH only ~ Pass
FIGURE 4-3 Results from Orange County study showing percentage of vehicles
identified by remote-sensing device (RSD) that failed IM240 and BAR90 emissions
tests. UH denotes under-hood inspection.
false failures attributed to cold-start operating conditions and mismeasured HC
emissions. Appropriate remote-sensing sites were scarce, sites were lost as
freeway ramps were widened, and the program was continually looking for
new sites is. Walls, Arizona Department of Environmental Quality, personal
commun. February 16, 2001~.
During a period from mid-May ~ 998 through early June ~ 999, over 2 mil-
lion valid remote-sensing testrecords were collected, but only 2,987 vehicles
were identified as high emitters (Wrona ~ 999~. Owners of vehicles identified
as high emitters were sent letters ordering them to submit their vehicles for
IM240 testing within 30 days. Abouthalf(55°/O) of vehicle owners responded
within this time period; en additional 15-20% of vehicle owners compliedIater,
after their vehicle registration was suspended. Of vehicles that reported for
testing, 42% passed the initial IM240 test, although a survey indicated that one-
third of these vehicles underwent repairs prior to the test (Wrona ~ 999~.
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Emerging Emissions Testing Technologies ~15
Use of Remote Sensing to Screen for Clean Vehicles
Remote sensing is being used to identify clean vehicles so that they may
avoid visiting an emissions test station for scheduled testing. For example, in
the St. Louis area, a clean-screen program has been in operation since April
2000. If two or more successive low-emissions readings have been measured
by remote sensing, the vehicle owner can opt to be excused from scheduled
emissions testing. Daily locations end hours of operation of remote-sensing
vans are advertised vie a web site. This clean-screenapproachmaybeprefer-
able to issuing blanket exemptions to all vehicles of specified model years.
ALTERNATIVE APPROACHES FOR
CONTROLLING LIFETIME EMISSIONS
An I/M program attempts to ensure that a vehicle's emissions-control
system is operating properly throughout the vehicle ' s lifetime. There are other
approaches to controlling lifetime emissions. Shifting the burden of responsibil-
ity from vehicle owners to the manufacturers is one approach. Although
requiring manufacturers to maintain vehicles throughout their lifetime might tee
unlikely, increasing warranties on emissions-controT systems to 200,000 miles
could accomplish at feast pert ofthis objective. Adopting national policies that
force older vehicles from the fleet is another option. Vehicle scrappage pro-
grams have been used on only a limited scale in the United States. Other
countries have taxation and inspection policies that help to maintain a young
vehicle fleet, but these policies tend to be in effect in places with a large do-
mestic automobile production sector (European Commission 1997; JAMA
2000~. Developing outreach and financial-support programs targeting owners
of high-emitting vehicles could be used to reduce the negative incentives for
those needing emissions repairs. These and the methods described earlier in
this chapter could be used to control lifetime emissions from vehicles and
reduce or eliminate the need for traditional I/M testing.
SUMMARY
Traditionally, I/M programs have used tailpipe emissions tests, often ac-
companied by visual underhood inspections, to assess vehicles registered in the
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116 Evaluating Vehicle Emissions I/M Programs
program area. This approach is inefficient and costly because of the skewed
distribution of emissions across the vehicle fleet; 10-20 mustbe tested to iden-
tify one high-emitting vehicle that is a candidate for repairs.
A variety oftechnologies that matured during the ~ 990s will affect emis-
sions testing regimes in the future. These approaches include developing
profiles of vehicles likely to have high or Tow emissions, use of OBD systems
to detect and help guide repairs of emissions-related malfunctions, and the use
of remote sensing to identify vehicles most likely to fail traditional tai1nine
emissions tests.
~ ~ -r -r -
The most significant form of profiling to date has been the excusing of new
vehicles (typically up to 4 years of age) from regular I/M program testing.
Smaller effects, if any, on emissions benefits and program costs have resulted
from profiles that rely on inspection history and results oftesting for vehicles
of the same make, model, and mode! year.
Although OBD systems are present on an increasing number of vehicles,
unresolved questions remain concerning their usefulness as a replacement for
traditional emissions tests. These systems detect malfunctions "likely" to lead
to increases in emissions above certification levels, but no actual emissions
measurements are made. Studies of emissions levels on vehicles with MTEs
illuminated have shown that most of these vehicles do not have emissions
much above their certification standard. A separate EPA study done with data
from Wisconsin's I/M program showed very little overlap between vehicles
that failed the IM240 and the OBD tests. The CDPHE also found a similar
result. instituting an OBD I/M program that fails a large number of marginal
emitters could undermine a commitment to find high emitters and ensure that
they are the repaired. Instituting an OBD I/M program that failed to detect
high emitters could do the same. Furthermore, a critical human factor for
OBD systems is the motorist's response to the MIL. The results of these
initial studies emphasize the inadequacy ofthe current data set for assessing
the effectiveness of OBD for I/M testing. The results also emphasize that
much additional information is required before OBDIT's reliability and effec-
tiveness canbe quantified in MOBILE. The modeling of OBD I/M options in
MOBILES is discussed in the following chapter.
Roadside remote sensing has been shown to measure CO emissions reli-
ably, with less certain results now available for HC and NOX. Development
of remote measurement capabilities for PM remains an important research
priority. A variety of issues require careful attention in remote-sensing study
design: site selection, effects of engine Toad, attention to quality assurance and
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Emerging Emissions Testing Technologies 117
quality control, and achieving adequate coverage of the in-use vehicle fleet.
Studies in which vehicles suspected to have high emissions based on remote-
sensing measurements are pulled over for further roadside testing have con-
firmed that remote sensing can identify vehicles likely to fail emissions tests
with a success rate of 80-96%.
Representative terms from entire chapter:
emissions testing
