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OCR for page 57
Vehicle I Inspection and
Maintenance Programs
This chapter descnbes the basic components of the inspection and mainte-
nance (I/M) program, the components that attempt to identify, diagnose, repair,
and verify repairs for vehicles with high emissions. The following sections
describe the venous network types, testing methods, and other elements of an
I/M program. Also discussed are results from some previous evaluations of
the effectiveness of existing programs.
AM PROGRAM NETWORK TYPES
The implementation structure of an I/M program, also known as "network
type," can have a major impact on its operation. Three basic network types
that are currently in operation are
~ Centralized.
· Decen~aTized.
· Hybnd.
Remote sensing establishes yet another testing type. 1 Each program type
States are now beginning to evaluate the feasibility of incorporating remote
sensing as an integral part of their I/M programs. For example, the Denver Regional
Air Quality Council has recommended beginning a "clean screen" program in January
2002, where on-road remote-sensing measurements would be used to exempt vehicles
from scheduled testing (Regional Air Quality Council 2000~. Missouri has been operat-
ing a remote-sensing clean screen program since early 2000.
57
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58 Evaluating Vehicle Emissions I/M Programs
has its strengths and weaknesses in terms of effectiveness, cost, and accep-
tance by the public, the repair industry, and politicians. The following sections
further describe the characteristics ofthe centralized, decentralized, and hybrid
network types.
Centralized Network
A centralized network consists of a relatively small number (relative to a
decentralized network) of stations that perform only emissions tests. Vehicles
that fad! the inspection must be repaired elsewhere. This network typically is
operated by a government entity or by a contractor with government adminis-
tration.
This system performs a high volume of emissions tests at Tow operating
costs. The centralized network can achieve an economy of scale in terms of
the investmentin equipment, inspector "raining, quality control, data collection,
and reporting. Program management, consisting of administrative and opera-
tional controls, is also more effective because there is better direct communi-
cation with the testing stations. The smaller number of stations associated with
a centralized testing network also simplifies program management.
Disadvantages of a centralized network include the need to make inspec-
tion stations convenient for the public while controlling costs for construction
and operation. Property conveniently located for the motoring public is often
diff~cultto find and/or very expansive. The centralized network wightbe more
inconvenient to the public because of fewer testing stations and longer travel
times to reach them. The centralized network also might tee more inconvenient
to the public when a facility is experiencing high demand due to test expiration
deadlines or lane closures due to equipment problems.
An additional disadvantage ofthe centralized network is the 'ping-pony"
effect. This happens when a vehicle fails the I/M test, obtains repairs at a
separate location, and returns to the I/M centralized network but fails again.
Some centralized networks have implemented measures such as the "repair
effectiveness index," which rates the effectiveness of repair stations to mini-
mize the ping-pony effect. Motorists can use this information to select a repair
station to minimize the need to go back and forth between testing and repairs.
Technicians in the repair industry might think they need to purchase emissions
analyzers to verify that the emissions repairs they perform allow the vehicles
to pass the test after repair. However, ina centralized network, this equipment
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Vehicle I/M Programs 59
would be purchased without the opportunity to collect a fee for the emissions
test verification.
Decentralized Network
A decentralized testing network consists of a larger number of Tow-volume
stations that do both emissions testing and vehicle repairs. This type of net-
work links testing to the repair process and is operated by private sector sta-
tions.
An advantage of the decentralized network is that it provides a revenue
stream from testing fees, which in turn may enable the repair industry to ac-
quire the training and skills needed to perform emissions-related vehicle re-
pairs. In addition, the repair technician can use the emissions analyzer to
verify the effectiveness ofthe repairs performed and eliminate the ping-pony
effect that can occur for some vehicles in the centralized network.
Program enforcement and quality control are more difficult in a decentral-
ized network than in a centralized program because of the larger number of
stations in the network.2 There can be more instances of fraud because of the
difficulty of overseeing all test stations. Test-and-repair stations have addi-
tional economic incentives notpresent in centralized test programs to fix vehi-
cles to pass (to please the customer),3 or to fail (to get more repair business).4
2There is no recent comprehensive study, however, to indicate that there are more
fraudulently passed vehicles occurring in decentralized programs. Testing fraud has
been reported in both decentralized and centralized programs. Since there are many
more stations performing inspections in the decentralized network, the number of
stations cited for testing fraud will likely be higher compared to a centralized program.
However, the number of inspections an individual station may be perfo~ing could be
low whereas testing fraud at a high-volume centralized testing facility may impact a
large number of tests. The committee could not find a rigorous comparison of these
program types to state definitively that the number of vehicles impacted by testing
fraud is greater in a decentralized program.
3Hubbard (1998) found that test-and-repair stations have an incentive to help
vehicles pass inspections to increase the long-term demand for their inspections, even
though they could increase short-term demand for emissions-related repairs by helping
vehicles fail.
4Both test-and-repair and repair-only stations may provide more repairs than are
actually needed (to make more money for the shop). Thus, some of the issues con-
cerning repairs will happen in centralized testing as well.
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60 Evaluating Vehicle Emissions I/M Programs
However, advances in the design of emissions analyzers are thought to have
made decentralized programs more effective by incorporating built-in quality
control, making analyzers less prone to tampering, and linking station data to
central data collection facilities.
Hybrid Program
A hybrid network is one that incorporates elements of both decentralized
and centralized programs. One type of hybrid program incorporates both high-
volume "test-only" stations and low-volume "repair-and-retest" stations. This
approach achieves economy in enforcement, data and program management,
and quality control for the initial test, which has the largest volume oftesting.
It also provides an incentive to the repair industry by allowing them to perform
the official retest and eliminates the problem of repaired vehicles having to
return to a centralized facility for the retest.
Another type of hybrid program sends a fraction of vehicles, such as those
fitting the profile of a vehicle having high emissions, to a test-only station and
allows others to choose to go to either a centralized station or a decentralized
test-and-repair station. Such a program attempts to ensure that vehicles most
likely to fail will undergo testing at facilities with the highest quality control. It
also provides fairly convenient testing for most vehicle owners at the decen-
tralized testing locations.
VEHICLE-EMISSIONS TESTING
Vehicle emissions tests vary in terms ofthe complexity of driving condi-
tions represented. An important issue is the need for the test to obtain an
accurate measurement of emissions while keeping equipment costs low and
test duration short.
Mass Emissions versus Concentration Measurements
The two principal methods of measuring exhaust emissions are (~) directly
measuring the mass of emitted pollutants, and (2) measuring the concentrations
of pollutants in exhaust emissions. These methods are known as mass emis-
sions tests and concentration tests, respectively.
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Vehicle I/M Programs 61
Mass emissions tests quantify vehicle exhaust emissions by measuring the
mass of various pollutants that are emitted. Generally, these emissions are
expressed as the mass of pollutant emitted divided by the distance the vehicle
is driven on a simulated driving cycle. In this type oftesting, a vehicle is driven
on a dynamometer and the results are expressed in terms of grams of pollutant
emitted per mile traveled.
Concentration tests, on the other hand, measure the relative pollutant
concentrations in a vehicle ' s exhaust. Because the measurement is a concen-
tration measurement (generally expressed in terms of percentage or parts per
million of total exhaust volume) little is known about the absolute amount of
pollution generated. For a given exhaust concentration, vehicles with larger
engines and higher fuel consumption will have higher mass emissions. To
understand the magnitude of actual emissions, both pollutant concentrations
and the volume of exhaust must tee known. The exhaust volume is measured
in some, but not all, of the emissions tests used in I/M programs. By knowing
the volume of emissions and airflow, it is possible to determine an average
mass emissions rate. Converting concentration testresults to mass emissions
introduces uncertainty in the estimates (Haskew et al. 1987~.
Steady-State Versus Transient Testing
Another way to differentiate vehicle emissions tests is by describing the
conditions under which emissions are measured. Emissions can be measured
under static or dynamic conditions, which are referred to as steady-state or
transient tests, respectively.
Steady-state tests measure vehicle emissions under one stable operating
condition. Typically, a vehicle is tested at idle, when no dynamometer is used,
or under steady speed with a simulated load when tested on a dynamometer.
Dynamometer-based tests, such as the acceleration simulation mode (ASM)
tests, are steady-state tests because they run the engine under a constant Toad
instead of varying the Toad throughout the test, as is done in transient tests.
Although steady-state tests do not simulate the range of driving conditions that
are included in transient tests, they require smaller expenditures for testing
equipment and may be performed in less time.
Transient tests require a vehicle to operate under varying speeds and
loads. They represent on-road driving conditions much better then steady-state
tests, and they are transitory in nature. In emissions testing, typically the speed
and acceleration ofthe vehicle are varied. By testing a vehicle under different
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62 Evaluating Vehicle Emissions I/M Programs
speeds and engine Toads, a broader range of emissions results is measured. To
obtain a measurement thatis more representative of emissions when vehicles
are driven on the road, test cycles have been developed that seek to replicate
actual driving conditions.
Exhaust Emissions Test Types
A number of tests are commonly used to measure vehicle exhaust emis-
sions. These range from unloaded idle tests to sophisticated transient-cycle
mass emissions tests, such as the Federal Test Procedure (FTP). Some ofthe
more common tests are described below.
Mass Emissions Tests
· FTP City Driving Test This is a loaded-mode laboratory grade
mass emissions test with transient (stop-and-go) driving conditions that is used
by vehicle manufacturers to certify the emissions of prototype vehicles before
they can sell the vehicle for the first time in the United States. It is usually
considered the benchmark emissions test by which all other light-duty vehicle
tests are measured. The FTP has extensive protocols, including specifying fuel
parameters and environmental conditions and requires large expenditures of
time, personnel, and capital. The test is split into various phases designed to
measure the emissions from cold-start, urban driving, and hot-start operating
conditions. To perform the City Driving Test (also known as the Urban Dyna-
mometerDriving ScheduTe) end all other elements ofthe FTP (includingpre-
paring the vehicle for testing), at least 2 days per vehicle are usually required.
A problem with the FTP has been that the test does not measure emissions
that occur during heavy acceleration or high-Ioad operating conditions that are
sometimes observed in on-road driving (Kelly and Groblicki ~ 993; St. Denis et
al. ~ 994; Cicero-Fernandez et al. ~ 997~. The Supplemental Federal Test Pro-
cedure (SFTP) was proposed in ~ 996 (EPA ~ 996) to control emissions et high
speed, at high load, and with the air conditioning operating.
IM240 This test is a shortened version of the FTP, in which the
vehicle is given minimal conditioning, and is assumed to be tested when fully
warm. Thus, it can be conducted outside the laboratory in a well-equipped
inspection station. It is a loaded-mode transient dynamometer test, which
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Vehicle I/M Programs 63
measures the mass of emissions collected over a 240-second, 2-mile driving
cycle that corresponds to the first 240 seconds ofthe City Driving Test ofthe
FTP (see Figure 3-~. Many states that utilize the IM240 test have imple-
mented a "fast/pass" or a "fast/fail" procedure orboth. This shortened version
can reduce the testing time by several minutes.
· BARS ~—This is a short, Toaded-mode dynamometer test utilizing
similar equipment as the ]!M240. The driving cycle has been truncated to 3 ~
seconds, with the vehicle sharply accelerating and then decelerating through
the test. A vehicle has three chances to pass the test.
· IM93/CT93 Connecticut 93 This test is a short version of the
IM240 test cycle, utilizing the first "hill" or phase ofthe IM240. It consists of
the first 93 seconds of the IM240.
IMI47 This is also a shortened version ofthe IM240, specifically~e
second phase (final 147 seconds). A major difference is the application of a
retest aigonthm that determines whether a failing vehicle needs preconditioning
before a final failure determination is made.5 A vehicle may be given up to
three consecutive IMI47 drive cycles before it fails.
VMASS The VMASS flowmeter system converts a concentration
measurement to a mass measurement. The test methodology could use any
transient I/M test cycle, such as the BARS I, CT93 , or IM I 47. In this system,
BAR97 type equipment (see below) is coupled to a transient dynamometer
Concentration Tests
~ idle test This steady-state unloaded test uses a tailpipe probe to
measure directly the concentrations of CO, HC, and carbon dioxide (CO2) in
exhaust emissions fromidling vehicles. A high-idle test,in which engine speed
is manually increased to ~2,500 revolutions per minute (~pm), is sometimes
performed in addition to the natural or "Iow-idle" test; in all cases, there is no
Preconditioning refers to a vehicle that is fully warmed up so that it can give a
valid result from an I/M emission test. Cutpoints, which determine passing or failing
for such a vehicle, are based on testing a fully warmed-up vehicle in which the
emissions control equipment, including the catalytic converter, are fully functional.
If an owner drives a short distance to the test station or if the vehicle has to wait in the
test station for a long time, the vehicle might not be fully warmed up, resulting in a
false reading; a car that would have passed if fully warmed (i.e., fully preconditioned)
would fail.
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64 Evaluating Vehicle Emissions I/M Programs
0
~ 30
~ ~ 20
In 10
o
FIGURE 3-1 IM240 driving cycle.
r
NO
L:
i,
~ .~.- .
0 50 100 150 200 2s0 300
Time (seconds)
load applied to the engine. NOx concentrations are not usually measured as
part of idle tests because NOx emissions are Tow if the engine is not under a
load. The idle test is less expensive than Toaded-mode testing because no
dynamometer is required. Although idle tests measure and report pollutant
concentrations, Marr et al. (] 998) describes how mass emissions rates (i.e.,
grams of pollutant emitted per minute at idle) can be calculated from engine
displacement volume, engine speed at idle, and measured tailpipe concentra-
tions from the idle test.
· ASM This series of loaded-mode steady-state emissions tests mea-
sures exhaust concentrations from motor vehicles operated on a dynamometer.
The test series measures vehicle emissions under a loaded condition that simu-
lates an acceleration event. The ASM steady-state test measures vehicle
emissions at ~ 5 (ASM 5015) and 25 (ASM 2525) mph. The tests subject the
vehicle to load conditions that are based on the maximum acceleration events
in the FTP. The ASM 5015 subjects a vehicle to 50% ofthe maximum load
conditions in the FTP test, and the ASM 2525 subjects a vehicle to 25% ofthe
maximum Toad conditions in the FTP.
~ BAR97—This refers to emissions testing equipment and software that
meet the ~ 997 California Bureau of Automotive Repair's specifications for use
in their I/M programs. The same test equipment may be used to perform
either the ASM or the idle tests described above. This test equipment is nor-
mally used for concentration measurements. When a BAR97 test analyzer is
used in conjunction with a VMASS flow meter, it is then used to measure
mass emissions. Earlier versions of the BAR analyzer specifications were
issued in ~ 984, ~ 990, and ~ 994. Analyzers that met prey 997 specifications
were usually used to perform idle tests only.
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Vehicle I/M Programs 65
· Remote sensing This is anonintrusive method of measuring emis-
sions from individual vehicles as they drive by a sensor deployed at a roadside
location. In normal operation, a beam of light is projected across a single lane
oftraffic et tailpipe height, and light absorbed by pollutants is measured, usually
at specific infrared wavelengths (ultraviolet light absorption is used in some
systems to measure NO emissions). Remote-sensing measurements are
Wpically coupled to a video image ofthe vehicle license plate, which can be
used to obtain vehicle make, model year, and other relevant information from
a central database.
Comparison of Exhaust Emissions-Test Types
.~
The California I/M pilot study (CARE 1996) provided the opportunity to
compare emissions results from several candidate exhaust test types: the FTP,
IM240, ASM5015, ASM2525, and low- and high-speed idle tests. In this
program, 380 vehicles due for their biennia! inspection were given all six emis-
sions tests. As a result, this sample was probably enriched in high emitters
relative to the whole vehicle fleet. The data were analyzed to compare differ-
ent emissions tests for measuring tailpipe CO and HC emissions. Figures 3-2
and 3-3 present the results, which are described further by [Lawson and
Koracin (1996~. In Figure 3-2, the CO emissions from the 380 vehicles were
rank-ordered from dirtiest to cleanest according to their FTP, IM240, ASM,
and idle-test results. For the ASM and idle tests, the maximum value from
either ofthe two ASM or idle tests was used. Figure 3-3 shows the results for
HC plotted in the same manner. The correlation among the different test types
is shown in Table 3- ~ . The statistic used is the Spearman rank-order correla-
tion,6 which is a statistical method that measures the correlation between ranks
oftwo sets of variables, rasher then their absolute values. The data from the
California I/M pilot study illustrate Adhere is considerable correlation among
different test types for measuring exhaust CO and HC. A similar comparison
oftest types has not been done for NOX, which is Wpically not in an idle test.
6A correlation coefficient measures the degree to which two variables are related.
For perfect positive correlation, the value ofthe correlation coeff~cientis +1; for perfect
negative correlation, the value is -1. A correlation coefficient of O means there is no
relationship between the variables. The Spearman rank correlation coefficient is a
nonparametric (distribution-free) statistic measuring the strength of the associations
between two variables when the variables are rank ordered.
OCR for page 66
66 Evaluating Vehicle Emissions I/M Programs
1.0
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-
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.
O 38 76 114 152 190 228 266 304 342 380
Vehicles Ranked by Emissions Reading
['1'~
.....
TM240
ASM
Idle Test
FIGURE 3-2 Comparison of FTP, IM240, ASM, and idle-test results for CO.
Replicate emissions tests were not performed for the 380 vehicles. Cor-
relation of readings from two sets oftests with the same set of vehicles is far
from perfect; Lawson (1995) reported an r-squared value of only 0.66 for
IM240 test results between I/M lane data and laboratory data for the same
vehicles.
Another comparison of different test types canbe done with results ofthe
Colorado's IM240 and idle-testprograms.7 Colorado's Automobile Inspection
and Readjustment (AIR) program operates an IM240 program for 1982 and
newer ears in the Denver metropolitan area, and a two-speed idle-test program
in three other counties in Colorado. Vehicles older than ~ 98 ~ in the Denver
metropolitan area are also tested with the two-speed idle test. A recent audit
of this program (Air Improvement Resource ~ 999) using data for calendar
year ~ 998 reported that the idle-test program given outside the Denver metro-
politan area had a higher failure rate than the IM240 tests given in the Denver
Additional comparison of test types could and should be done, including
comparing an annual idle test program for HC and CO with a biennial IM240 test
program. Emissions-reduction benefits of a biennial idle-test program could be
compared with a biennial IM240 test program in which both had approximately the
same failure rates.
OCR for page 67
Vehicle I/M Programs 67
1.0
° 0.8
a
.g
V 0.6-
~ 0.4-
o
,
80.2
0-0- ~
0 38 76 114 152 190 228 266 304 342 380
Vehicles Ranked by Emissions Reading
~''m
/"' '/
/.'/
~ ,
b'1'~
IM240
ASM
Idle Test
FIGURE 3-3 Comparison of FTP, IM240, ASM, and idle-test results for HC.
area ~ ~ 6.7% versus 5. ~ %), a smaller emissions-reduction benefit per repaired
vehicle (23% versus 58%), and a similar overall emissions reduction (6.5%
versus 6. ~ %) compared with vehicles tested with the IM240 test. Average
repair costs for the idIe-tested vehicles were $95 per repair versus $2 ~ ~ for the
IM240 tested vehicles. Both achieved about the same level of CO benefit in
~ 998. However, the idle test does not measure NOx, and while it fails more
vehicles, average emissions reductions and costs per repair are less. No at-
tempt was made to determine whether differences between the vehicle fleets
in the Denver metropolitan area and the nonmetropolitan Denver counties
caused any of these differences.
Evaporative Emissions Tests
Exhaust emissions are relatively easy to sample for routine inspection the
exhaust exits from the tailpipe and a collection hose is attached to the tailpipe
for testing. Evaporative emissions can occur from many places on the vehicle.
The fuel tank, filler neck, and gas cap are typically at the rear of a vehicle.
The engine's file] components are at the front, perhaps 12 feet away. If one
tries to detect the presence of leaks from the system, the entire vehicle must
OCR for page 79
Vehicle I/M Programs 79
repair resulted in a range of estimates. Using the roadside pullover data, the
IMRC calculated an emissions reduction of 17% for HC and 9°/O for NOX.
The IMRC also concluded that ~ 0°/O of all vehicles that failed the initial
Smog Check test never received a passing mark in later tests. This estimate
is lower than that observed in Phoenix, where an estimated 29% of vehicles
that failed the initial IM240 test never received a passing test or waiver in the
following 3-15 months (Wenzel 1999a), and in Denver, where 27% of the
e m i s s i o n s f a i 1 u r e s a r e u n r e s o l v e ~ ~ A i r ~ m p r o v e m e n t R e s o u r c e 1999 ~ . A n o t h e r
5- 10% ofthe vehicles observed on-road in California were eligible for Smog
Check testing, but no records exist of these vehicles reporting for a test.
Earlier independent evaluations of California' s ong~nal decentralized idle-
testprogram showed no emissions-reduction benefit (Lawson 1993; Lawson
et al. l 995,1996a). That result was based on data collected from California's
random roadside surveys from 1989,1990, and 1991 and it is in contrast to the
estimate that the program using the CARE I/M model (the CALIMFAC
model) was producing emissions reductions of 18°/O HC, 15% CO, and 7°/O
NOX (IMRC 1993) at that time, and to data from vehicles that were given
emissions tests before and after repairs.
Colorado AIR Program
The 1999 audit of Colorado's AIR program used test data on the outcomes
of failing vehicles as well as EPA's Serious CO Area Models to estimate
emissions reductions (Air Improvement Resource 1999~. Directed at reducing
CO emissions, the AIR program operates in metropolitan areas along the Front
Range (Denver area, Colorado Springs, Fort Collins, and Greeley). As de-
scnbed earlier, the program consists oftwo types oftests: a centralized bien-
nial TM240 test used in the Denver area for 1982 and newer vehicles, and an
annual basic idle test used in other areas and for vehicles older than 1982 in the
enhanced area. The emissions reductions were estimated one time by analyz-
ing the changes in emissions for fail-pass vehicles (vehicles that initially failed
an I/M program and then passed a retest) tested during 1998 and part of 1999.
i°The Serious CO Area model is a forerunner of the MOBILE6 model made avail-
able by EPA to states completing CO planning activities. It utilizes the lower emissions
deterioration rates that will be contained in MOBILE6 and reduces the credits for oxy-
genated fuels.
OCR for page 80
80 Evaluating Vehicle Emissions I/M Programs
The reductions were then used to estimate the benefits for the whole vehicle
fleet. A second estimate of emissions reduction was made with EPA's Seri-
ous CO Area Model. This mode! reflects the assumptions that will be con-
tained in the new MOBILES, which probably will result in substantially lower
credits for I/M programs than were estimated by MOBILES. Overall, the
evaluation concluded that, depending on the method of analysis, the AIR pro-
gramreduced 1999 CO emissions by 8-17%. The Tower estimate of emissions
reductions was produced by using the in-program emissions data on fail-pass
vehicles and by analyzing remote-sensing data from the area. The higher
estimate was produced with the Serious CO Area Model.
Earlier evaluations ofthe Colorado program estimated differentbeneiits.
Stedman et al. ~ ~ 997) estimated a 4-7% CO emissions-reduction benefit based
on remote-sensing measurements. This evaluation showed no HC and NOx
emissions reductions and no CO emissions reductions for pre-1 982 vehicles.
In another study, Stedman et al. (1997) estimated an 8-1 I°/O benefit teased on
the same measurements. ENVIRON International Corporation (1998) also
funded a study that reported that the program obtained a 20-34% CO benefit
using EPA's MOBILES model.
Independent Evaluations of State I/M Programs
In addition to the evaluations of I/M programs in Colorado and California
described earlier in this report, numerous evaluations have been done by state
agencies, EPA, and independent researchers. The following section describes
a selection ofthese evaluations. Pierson (l 996) also summarizes earlier I/M
program evaluations.
Evaluation of Phoenix's Program
Several studies in the past few years have examined the performance of
the enhanced centralized IM240 program in Phoenix, Arizona. In addition to
the thousands of records of program data gathered, extensive remote-sensing
data were also collected. Several independent researchers such as Wenzel
( 1 999a) and Harnngton et al. ( l 99S, 2000) performed studies using this infor-
mation. EPA also assessed the performance of the Phoenix program using
only I/M test records (EPA ~ 997a). Results from the studies are shown in
Table 3-4.
OCR for page 81
81
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OCR for page 82
82 Evaluating Vehicle Emissions I/M Programs
The EPA analysis ( l 997a) compared predictions of the TECH5 compo-
nent of the MOBILE mode! used in the Phoenix case with the emissions re-
duction calculated from the IM240 test datable The results predicted by the
mode} were only slightly greater for HC reductions, but they were substantially
higher for NOx reductions (Table 3-4~. Chapter 5 provides a detailed discus-
sion of the emissions-reduction benefits estimated for I/M with MOBILE.
Also included in Table 3-4 are the original predictions for the IM240 pro-
gram from EPA's regulatory impact analysis of enhanced I/M in 1992 (EPA
~ 992b). Even though these estimates are the results of comparisons between
enhanced I/M and non-T/M programs, they are probably close to what Phoenix
is actually being granted in SIP credits. This is due to the MOBILE mode}
predictions of low emissions reductions (5% for HC) from basic I/M programs.
As shown in Table 3-4, the MOBILE model forecasted greater HC and
CO emissions reductions than were actually found using in-program or remote-
sensing data. The large reductions predicted by the model were originally
based on the assumption that all failing vehicles would be repaired. In Phoenix,
however, the program data showed that roughly 25% of them had still not
passed ~ year after failing the test (Ando et al. 2000~.
Harrington et al. (2000) examined the costs and emissions reductions of
the Phoenix program by using all IM240 test results over a period of ~ 7 months
(January ~ 996 to May ~ 997~. This study used emissions data of initial and final
tests for failed vehicles and assumed that emissions repairs lasted 2 years.
Given these assumptions, the study estimated that HC emissions were reduced
by ~ 3°/O and NOX emissions by 7°/O over the 2-year penod. This finding was
very similar to the EPA (1997a) results from program data.
Wenzel ~ ~ 999a) compared emissions reductions based on IM240 test data
with a large sample of remote-sensing readings. The results ofthis study for
the Phoenix program data were similar to those of the Harnngton et al. (2000)
study, which was also based on test data from the program. Wenze} found,
however, that the emissions reductions were lower when remote-sensing
readings were used; HC reductions were ~ 1°/O instead of 14%. Furthermore,
the ~ 1°/O remote-sensing readings included a relatively large share of pretest
reductions, which would not be reflected in the program data. These pre-
inspection repairs are observed in remote-sensing data, which show a reduc-
tion in emissions In vehicles ~ -2 weeks before their inspection (Wenzel ~ 999a),
lathe TECHS component of MOBILE was modified in this work to reflect
emissions reductions that occur in a single I/M cycle. These model modifications are
described in EPA (1997a, pp. 12-13~.
OCR for page 83
Vehicle I/M Programs 83
as well as survey data, which indicated that a significant fraction of motorists
had their vehicles tuned up before inspection (IMRC 20001. The implication
of these findings is that the remote-sensing results show substantially lower
post-inspection emissions reductions than the in-program data.
Evaluation of Minnesota's Program
Scherrer and Kittelson ~ ~ 994) assessed the impact on air quality of an I/M
programinitiatedinI99linM~nneapolis. Direct measurements ofambientCO
data et three monitoring sites were used. Assessing the effectiveness of I/M
using CO air-quality data is appearing because a high fraction of CO is emitted
by light-duty vehicles subject to such testing, and CO is relatively unreactive
in the atmosphere. Minnesota's centralized I/M program consisted of an idle-
testprogram for HC and CO that failed about 9.4°/O of vehicles dunng its first
year(July 1991 to June 1992~. This study used amultifactorairegression that
corrected for vehicle activity and meteorological factors to discern I/M bene-
fits from time series observations of CO concentrations. The study collected
hourly ambient CO monitoring data in the city and meteorological data at the
regional airport. The average ambient reduction of CO attributed to I/M was
~ .3 ~ ~ .4°/O, with individual sites showing a 5.~°/O decrease, a ~ .5°/O decrease,
and a 3.4°/O increase.
Using air-quality data to evaluate I/M emissions benefits raises many
issues. The committee recognizes that observing the effects of I/M programs
on air quality is difficult because the level of emissions reductions have been
relatively modest and there are numerous confounding variables. One of the
issues encountered in this study related to the methods used to correct for the
effects of changes in vehicle activity patterns and the vehicle fleet itself. The
wide range of changes in ambient CO levels, estimated at the three monitoring
sites, also suggests that using a limited number of monitoring sites for the
purpose of program evaluation might tee unreliable. However, it is those moni-
tors that define whether a locality is in nonattainment of the national ambient
air-quality standards and trigger the need for an I/M program.
Evaluation of Georgia's Program
The Air Quality Laboratory at Georgia Institute of Technology used re-
mote sensing to determine the influence of city characteristics on motor vehicle
OCR for page 84
84 Evaluating Vehicle Emissions I/M Programs
emissions (Rodgers 2000~. The reference method of evaluating I/M's benefits
(discussed in Chapter 6) compares vehicle emissions in an I/M city with those
of a reference fleet in a city with similar socioeconomic and meteorological
characteristics but with a different I/M program. This reference fleet could
be from a non-~/M city in which case an evaluation would determine the
reduction in emissions due to the I/M program—or from a city with a bench-
mark I/M program. In the latter case, the evaluation would compare how well
the program performed relative to the benchmark. The Air Quality Laboratory
studded whether the selection ofthe reference fleet could effect the evaluation.
It looked at whether emissions in comparable cities were actually similar.
Because of similar socioeconomic characteristics, fleet age distribution, and
average model year emissions, the I/M cities of Nashville, Tennessee, and
Atlanta, Georgia, had comparable fleets for application ofthe reference meth-
od. Other city comparisons (Boston, Massachusetts compared with Burling-
ton, Vermont; Macon, Georgia compared with Augusta, Georgia), however,
suggested that characteristics outside of I/M program status can result in
dissimilar model-year emissions. That result points to the difficulty in i inding
a comparable fleet for use in the application of the reference method.
The Air Quality Laboratory also used remote-sensing data to evaluate the
emissions-reduction benefits for Atlanta's I/M program. Until 1999, the I/M
program included a decentralized idle test in the four counties in the central
Atianta metropolitan area. The Air Quality Laboratory study compared emis-
sions in the I/M area with emissions in the surrounding nine counties, which
were not subject to an I/M program at the time. From this study, a reduction
in CO emissions of 7.5°/O was estimated. Note that no attempt was made to
correct for socioeconomic differences between the I/M and non-~/M areas.
Atlanta' s I/M program expanded to include these nine surrounding counties in
~ 996. Using more recent data, the Air Quality Laboratory also estimated the
benefit ofthe program by comparing emissions of vehicles that had been tested
with those that had not been tested when the program expanded to include the
surrounding nine counties. This method (the step method described in Chapter
6) yielded an ~ 1°/O reduction in CO emissions.
EPA's National Tampering Surveys
For a number of years, from the latter ~ 970s to the early ~ 990s, the EPA
conducted motor vehicle tampering surveys at various locations throughout the
OCR for page 85
Vehicle I/M Programs 85
country. EPA used data from these surveys to document the occurrence of
tampering-related defectsi2 in the motor vehicle fleet and to compare different
I/M program types for effectiveness. Random roadside surveys allow for
inspection of vehicles as they are driven on the road, but many EPA surveys
of centralized programs were done in the test lane, rather than on the road,
which introduces bias into the results. Motorists were given no advance notice
that they wilIbe stopped for aninspection. The date collectedin those surveys
also give a representative sampling of actual vehicle miles traveled, because
the more a vehicle is driven, the more likely it is to be stopped. Participation
in the surveys was voluntary, so the survey results probably are biased toward
vehicle data from compliant motorists who are generally willing to participate
in such surveys.
In each year's survey, EPA selected up to ~ 5 cities as sampling sites. To
obtain statistically meaningful data, 300-500 vehicles were inspected et each
location. The mix of inspected vehicles was assumed by EPA to be a self-
weighting sample, and no attempt was made to approximate the national vehi-
cle mix. The sampling location and the method of stopping individual vehicles
varied for each location in accordance with the type of I/M program in place.
Sampling also occurred in non-/M areas. The roadside inspection included the
following:
· Basic vehicle identification data
· Check of all emissions-control system components
· Measurement ofno-Ioad, Tow-idle (~IOOOrpm) HC end CO emissions
· Collection offuel sample from unTeaded-only fueled vehicles forlead
analysis
· Inspection of fuel inlet restrictor (designed to prohibit fueling with
leaded gasoline)
· Test of tailpipe for lead deposits
Lawson et al. (l 995) performed a series of analyses using EPA's national
tampering survey data, obtained through roadside surveys, to compare the
effectiveness of centralized and decentralized I/M programs with no I/M
program. One study used pass-faiT rates for the 44,000 vehicles reported,
according to tampering inspection and emissions-test results from the EPA
"Tampering" is the malfunctioning of one or more emissions-control devices due
to either deliberate disablement or mechanical failure.
OCR for page 86
86 Evaluating Vehicle Emissions I/M Programs
survey data taken from ~ 985 to ~ 990. The data were adjusted for model year
and mileage. The model-year categories are ~ 985- ~ 990, ~ 980- ~ 984, and pre-
~ 980, corresponding roughly to fairly homogeneous em~ssions-control technolo-
g~es, although some differences for catalyst technologies and trucks and light-
duty vehicles span these model-year groupings. Mileage was divided into five
categories, the highest including 100,000 or more miles, as recorded on the
vehicle's odometer. Finally, within each model-year group and mileage inter-
val, vehicles were categorized according to the type of I/M program where
they were sampled.
As shown in Figure 3-4, each combination of mileage and year of manu-
facture was compared for mean values of overall failure rates from different
types of I/M programs: none, decentralized, and centralized. This plot displays
the following features: failure rates tend to increase with odometer reading
and vehicle age and to be highest for the oldest technology vehicles. Neither
centralized nor decentralized programs showed a much Tower failure rate than
vehicles from non-/M program areas.
In a second study, data obtained in these surveys over an S-year period
( 1985- l 992) were adjusted for differences in vehicle age and odometer read-
ings (Lawson et al. ~996a). The analyses also accounted for the type of I/M
program in place in each ofthe areas where the surveys were made. Tamper-
ing and emissions failure rates for different I/M configurations during the ~ 985-
~ 992 period are presented in Table 3-5, which shows that there were only
small differences between different I/M program configurations. There was
also only a 4°/O difference in tampering or emissions failure rates between non-
]:/M and centralized areas, a small difference compared with the overall emis-
sions and tampering failure rates. Because EPA discontinued its motor vehicle
tampering surveys after ~ 992, more recent analyses with nationwide data have
not been possible.
SUMMARY
Numerous variations of vehicle emissions I/M programs are in use today,
each with its own attributes. One program type is the centralized program
using transient emissions tests such as the IM240. Such programs enable the
estimation of mass emissions of NOx, CO, and HC under simulated Unving
conditions. Possible drawbacks from this type of program are higher testing
equipment costs and greater inconvenience to the public because of fewer
testing locations. Additionally, motorists requiring repairs must visit a separate
OCR for page 87
87
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OCR for page 88
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OCR for page 89
Tampering HC >100 HC > 400
Program Type Rate (%) ppm (%) ppm (%) CO > 1 (%) CO > 4 (%)
Non-I/M 19.5 28.0 8.8 20.8 10.4
Vehicle I/M Programs 89
TABLE 3-5 Normalized Tampering and Emissions Failure Rates by program
Type from EPA's 1985-92 Motor Vehicle Tampering Surveys
Decentralized 16.6 25.7 7.9 18.5 8.7
Centralized 15.4 24.3 5.8 16.3 6.2
(on-road)
Centralized 15.0 26.6 5.7 14.7 5.6
(I/M lane)
repair facility before they return to be retested. Another type of I/M program
uses a decentralized idle test in which exhaust concentrations of HC and CO
are measured. Such programs provide greater convenience to motorists be-
cause ofthe larger number oftesting facilities, andbecause testing end repairs
can occur at the same place. These programs, however, do not simulate NOX
emissions and are more difficult to oversee. Many variations on these two pro-
gram types exist. For example, the current California Smog Check program
is a hybrid network that uses an ASM test to estimate CO, HC, and NO
concentrations.
Previous evaluations of I/M's emissions benefits have been based on
MOBILE as well as direct estimates of vehicle emissions. The committee
believes those evaluations based on direct estimates of vehicle emissions are
far superior to those taken from models. Estimates of I/M benefits from direct
measurements of vehicle exhaust using test data, remote sensing, end roadside
pullovers have shown reductions to be significantly smaller than model-pre-
dicted reductions. This conclusion is based on a review of state-sponsored
evaluations ofthe Colorado and California programs and independent evalua-
tions of these programs and programs in Arizona, Minnesota, and Georgia.
Although an exhaustive review of all previous evaluations is beyond the scope
of this study, the committee believes those described represent some of the
best examples of I/M evaluation. The committee recognizes that the number
of evaluations will expand greatly in the future. As discussed in Chapter 1, this
is the first phase of a two-part study. The second phase is expected to con-
tinue to review evaluations and to rely on them as critical sources of informa-
tion.
x
Representative terms from entire chapter:
vehicle emissions
