EPA-AA-IMS/81-10
Technical Report
Update on the Fuel Economy Benefits
of Inspection and Maintenance Programs
by
R. Bruce Michael
April 1981
NOTICE
ical Reports do not necessarily represent final EPA decisions of
positions. They are intended to present technical analysis of issues using
data vbich are currently available. The purpose in the release of such
repcrzs is to facilitate the exchange of technical information and to inform
the cublic of technical developments which may form the basis for a final EPA
decision, position or- regulatory action.
Inspection and Maintenance Staff
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air, Noise and Radiation
U.S. Environmental Protection Agency
Ann Arbor, Michigan
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Table of Contents
Section Heading
1.0 INTRODUCTION AND SUMMARY
1.1 Purpose
1.2 General Method
1.3 Sucrrnary of Key Results
2.0 BASIC I/M FUEL ECONOMY BENEFITS
2.1 Description of the Basic I/M Program
2.2 Fuel Economy Benefits for Repaired Cars
2.3 Fleet Average Fuel Consumption Benefits
3.0 OPTION 1: EXTRA FUEL SAVINGS FROM USE OF THE
TWO-SPEED IDLE TEST OR'LOADED TEST ON 1981
AND LATER VEHICLES
4.0 OPTION 2: EXTRA FUEL SAVINGS FROM
MECHANIC TRAINING
5.0 . OPTION 3: EXTRA FUEL SAVINGS FROM TIRE
PRESSURE CHECKS AT I/M STATIONS
6.0 SUMMARY OF OPTIONS AND THE OPTIMAL PROGRAM
REFERENCES
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APPENDIX METHODOLOGY FOR REPORT
1.0 INTRODUCTION
2.0 DATA NECESSARY FOR FINAL CALCULATIONS
OF FUEL CONSUMPTION
2.1 Registration Fractions of Each MYR
2.2 Average Miles Traveled for Each MYR in
the Preceeding 12 Months
2.3 Fraction of Diesel Cars in Each MYR
2.4 Average Miles Per Gallon (MPG) of Each MYR
2.5 Fleet Size and Total Vehicle Miles
Traveled (VMT) of All Passenger Cars
3.0 FUEL CONSUMPTION CALCULATION
4.0 CALCULATION OF BENEFITS
5.0 SAMPLE CALCULATION
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1.0 INTRODUCTION AND SUMMARY
1.1 Purpose
The purpose of this report is to present an updated assessment of the fue.l
economy benefits of Inspection and Maintenance (I/M) programs, in terms of .
individual vehicle and fleetwide savings, using the latest EPA test data. An
update of these benefits was needed to .incorporate the latest available data.
In addition, previous analyses [1, 2]* focused mainly on fuel economy improve-
ments for vehicles which fail an I/M test and are repaired, and did not
present a fleetwide or national picture of the fuel savings. This report
presents the fuel economy benefits which will result from a basic I/M program
(no mechanic training or other options) and the incremental benefits due to
adding options to the basic program.
The basic or "typical" I/M program analyzed is an annual one with idle
emissions inspections of all gasoline powered passenger cars of model years
1968 and newer. The three options which are analyzed are a more effective
test — either the Two-Speed Idle Test or the Loaded Test -- for 1981 and
later vehicles, a mechanic training program, and a tire pressure check
conducted as part of the I/M inspection.
Fuel economy benefits are shown for the first five years of a typical I/M
program assumed to start January 1, 1983 and are presented in three ways: (1)
average dollar savings and percent savings to owners of repaired cars during
the five years, (2) average dollar savings and percent savings .in fuel bills
for all I/M car owners, and (3) national fuel savings. - .
1.2 General Method
For each of the five calendar years .covered, a determination., of the fuel
economy benefit for each model year vehicle was made. It was necessary to
account for the fact that there are different numbers of cars in service for
each model year, they travel different mileages each year (as cars get older
they travel less and less, on the average), and they have different average
fuel economies (mpg). Also calculated was the effect the fuel -economy
improvement among the failed vehicles had on the entire I/M fleet and on
national fuel consumption. • _ . ' : . • : .
1.3 Summary of Key Results . . •
Tables 1 and 2 summarize the annual fuel economy benefits of I/M. Table 1
presents the fuel savings in terms of dollar and percent savings for the basic
I/M program and for an optimum I/M program that includes all of the options.
Benefits for the basic program are shown separately for repaired vehicles and
for all inspected vehicles. The average benefit per inspected vehicle in the
basic program is $3, which will offset a significant portion of a typical
inspection fee. The average benefit per inspected vehicle is $23 in the
optimum program. This would easily pay for the entire cost of an I/M
program. Table 2 presents the national fuel savings from the basic I/M
program and the optimum I/M program.
* Numbers in brackets refer to references listed at the end of the body of the
report.
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Program Type
Basic Program
Optimum Program
A
Table 1
Sunur.ary of Annual I/M Fuel Ec'onomy Benefits I7
Benefits per
Benefits
Repaired
Dollars
Saved
$7
N/A y
Vehicle £/
Fuel
Saved
0.8%
N/A y
Inspected
Dollars
Saved
$3
$23
Vehicle 3'
Fuel
Saved
0.3%
2.5%
I/ In 1980 dollars. .
21 In 1985.
3/ Average annual benefits for the five year period 1983 through 1987*
4/ The optimum program includes tire inflation (and the associated fuel
savings) for some vehicles which pass the I/M test and do not get
repaired. Benefits therefore cannot be properly expressed on the basis of
repaired vehicles.
Table 2
Nationwide Annual Fuel Savings from I/M J-/
Program Type
Basic Program
Optimum Program
Gallons Saved
(Millions)
83.6
701.4
JL/ Average annual savings over the five year period 1983 through 1987.
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2.0 BASIC I/M FUEL ECONOMY BENEFITS
2.1 Description of the Basic I/M Program
The basic I/M program was selected to be typical of new I/M programs which
will begin operation in 1982 or 1983. The basic program has the following
features:
Test Type - The test consists of a simple idle tailpipe emissions test for
hydrocarbons (HC) and carbon monoxide (CO). A vehicle must have lower
emissions than the limits for both pollutants in order to pass the test.
Inspection Standards and Failure Rate - For pre-1981 model year vehicles, the
analysis assumes that the I/M program officials select inspection outpoints
which result in a 20% failure rate. For 1981 and later vehicles, the analysis
assumes that the program officials select cutpoints of 1.2% CO and 220 ppra
HC. With the idle test, these cutpoints are expected to fail between 5 and 10
percent of the 1981 and later vehicles. Where a specific failure rate for
1981 and later vehicles was needed in this analysis, 7% was used. The results
of the analysis are also applicable to I/M programs with looser cutpoints for
1981 and later vehicles since the failure rate for these vehicles does not
vary much with cutpoints in the range of 1.2-3.0% CO and 220-300 ppm HC.
Starting Date - The analysis assumes that I/M starts January 1, 1983. Fuel
economy benefits are calculated for the first five years of the program,
through December 31, 1987,
Mechanic Training - No mechanic training occurs in the basic program.
Annual Inspections - All vehicles are inspected annually. New vehicles are
inspected at the first anniversary of their entry into service.
Vehicle Coverage - The basic program assumes all 1968 and newer gasoline
powered passenger cars have mandatory inspections; no trucks, motorcycles, or
diesel powered passenger cars are inspected.
Cost Waivers— No repair cost waiver provisions are assumed.
2.2 Fuel Economy Benefits for Repaired Cars
2.2.1 Method.of Fuel Economy Measurement
A combination of city and highway driving was chosen to measure fuel economy
benefits. The combination is the EPA combined figure of FTP (city) and HFET
(highway) driving cycles, which weights the city cycle 55% and highway cycle
45%. This is the same combination on which the new car fuel economy standards
is based. It was chosen so as to reflect all driving conditions. It should
be noted that the fuel economy changes measured on only the FTP would have
shown larger I/M benefits, however that cycle does not reflect all driving
conditions.
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2.2.2 No Fuel Economy Benefit for Pre-1981 Cars Vit'r.:ur Mechanic Training
Substantial data fron the EPA Portland Study, which scucied the operating I/K
program in that cityj show no net change in the average fuel economy of
pre-1981 vehicles due to maintenance of failed vehicles as it is currently
performed by the commercial repair industry[l].
2.2.3 Fifteen Percent Fuel Economy Benefit for 1981 and Later Cars Which Have .
Certain Failure Modes
For 1981 and later vehicles the fuel economy benefit from certain I/M repairs
will be is relatively large. Most 1981 and later vehicles are expected to
employ microprocessor-based engine control systems. These systems have been
found in the field to be vulnerable to fuel systen failures which result in
high emission levels and reduced fuel economy. I/M will pinpoint vehicles
with these failures and cause them to be repaired. EPA estimates that in the
absence of I/M, 5% of the 1981 and later fleet will have experienced such a
failure at 10,000 miles and that an additional 2% of the fleet experiences a
failure in every 10,000 cile increment. For this analysis I/M was assumed to
identify 50% of these failures with the idle test. (The idle test also fails
some vehicles for other problems, bringing the total failure rate to 5-10%.) .
The only way for these vehicles to pass an I/M retest is..to have their fuel
system restored to proper operation. A significant fuel economy benefit, 15%,
has been observed to accompany such repairs[3],
2.3 Fleet Average Fuel Consumption Benefits ..
2.3.1 Average Benefits for All 1981 and Later Vehicles
In order to determine the year-by-year benefits for these vehicles a special
modification of an EPA computer program named M03ILE2 was used. MOEILE2
normally is used to calculate I/M emissions reduction benefits, but was
modified to calculate fuel economy benefits. First, the average fuel consump-
tion of the 1981 and later fleet without I/M was calculated. Second, the
average fuel consumption with I/M was calculated using the 50% identification
rate for the vehicles with fuel system failures. Both averages accounted for
deterioration in fuel economy with mileage. The two were then compared to
yield a fleetwide fuel economy benefit for each year. For a more complete
description of these calculations, see Reference 3.
Due to the projected growth rate of vehicles experiencing a system failure,
and the fact that there will be more and more of these vehicles in service
each year, the fuel economy benefit for the 1981 and later fleet increases
each year. The benefits for each year of the assumed program are given below.
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Table 4
Basic I/M Fuel Economy Benefit for 1981 and Later Vehicles (Idle Test)
Calendar Fleet Fuel Economy
Year Improvement
1983 .42%
1984 .54% .
1985 .64%
1986 .78%
1987 .86%
2.3.2 Pre-1981 Vehicles Averaged with 1981 and Later Vehicles
Pre-1981 vehicles receive no benefit in the basic program. TJheir average fuel
consumption is averaged with the 1981 and later vehicles in the witli-and
without-^I/M cases to yield tha fleet fuel consumption with and without I/M.
The general method is to determine the vehicle miles travelled (VMT) of each
model year subject to I/M for each calendar year. Dividing each model year's
VMT by the estimated fuel economy (without I/M) for that model, year yields the
total gallons consumed. The summation of each model year's consumption yields
a fleetwide consumption without I/M. To get the fleet fuel consumption with
I/M, the percent benefit can be applied to the 1981 and later vehicles, and a
new summation calculated..
Details of the calculation are presented in the Appendix.
2.3.3 Gasoline Price
Estimated prices are based on a 1980 dollar level so as to show a- stable
reference for the fuel cost savings. The estimated price increase in gasoline
over and above increases due purely to general inflation, according to the
Congressional Budget Office, is 2.4% per year through the 1980's. For the
five year period of this paper, the estimated price is shown in Table 5.
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Table 5
Estimated Gasoline Prices in 1980 Dollars
f
Calendar Year Price per gallon
1983 $1.54
1984 $1.58
1985 $1.62
1986 $1.66
1987 $1.70
2.3.4 Average Annual Savings For I/M Repaired Vehicles
Owners of vehicles which fail the I/M test want to know what fuel savings they
will receive as a result of having their cars repaired. As stated in Section
2.2 there are no fuel economy benefits for pre-1981 vehicles and a 15 percent
average benefit associated with repair of certain failure modes for 1981 and
later vehicles which fail the I/M test. There are also other types of failure
modes expected to occur on 1981 and later vehicles which tnay yield no fuel
economy benefit with repairs. Therefore, the average benefits for 1981 and
later vehicles which fail are composed of one group receiving 15% benefit and
another receiving no benefit. For the purposes of this analysis the total
failures are estimated to be 7% of the 1981 and later fleet.
To calculate the individual vehicle benefits, it x?as necessary to look at only
one representative calendar year. The 1985 calendar year was chosen, because
it is the middle year and therefore the most represenatative. During that
year it turns out that of the 7% of 1981 and later vehicles which fail, 1.68%
are estimated to be of the type which receive a 15% fuel economy benefit and
5.32% of the vehicles have other types of failures which receive no benefit.
The average benefit for all the failures of 1981 and later cars is therefore
3.61%. To get an average benefit for all failed vehicles, the percent changes
were weighted for the number of expected failures for pre-1981 vehicles (20%
of the total number of those vehicles) and for 1981 and later vehicles (7%).
The dollar and percent benefits are shown in Table 6.
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Table 6
Basic I/M Fuel Savings in 1985
Repaired Vehicles Only
Dollars Saved Fuel Saved
Pre-1931 Vehicles 0 0 .
19SI and Later Vehicles $ 32.08 3.61%
Overall $ 6.88 0.77%
2.3.5 Average Annual Savings for Inspected Vehicles
It is important to be able to estimate the annual fuel savings to all owners
of vehicles involved in I/M. A reasonable way of presenting the savings is
sinply the average per inspected vehicle (the sum of the savings divided by
the total number of vehicles inspected). Note that the savings do not apply
to vehicles that are too new to be inspected or those older than the 1968
code! year. Savings for the basic program are shown beloy in Table 7. The
snnual savings shown in the table are the averages for the five year period
1983 through 1987.
Table 7
Basic I/M Annual Fuel Savings Per Inspected Vehicle
Dollar Savings Fuel .Savings
$2.74 0.29%
2.3.6 National Savings
Section 2.3.2 outlines the method used to calculate the fleet fuel consumption
with and without I/M. To determine the national benefits it is necessary to
know how many vehicles will be in I/M areas. Based on State Implementation
Plans (SIP's) submitted to EPA in 1979 and 1980, EPA estimates that 45% of the
national "vehicle population will, be in I/M areas, and therefore that 45% of
the VMT are contributed by vehicles in the I/M areas. The number of gallons
saved is obtained from the VMT per model year, the average miles per gallon
for each model year without I/M, and the percentage fuel consumption decrease
due to I/M. The national fuel savings per year are shown in Table. 8.
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Table 8
Nationwide Annual Fuel Savings from the Basic I/l-i Progr^
Gallons Saved
Calendar Year (millions)
1983 27
1984 50
1985 80
1986 117
1987 144
Average 83.6
3.0 OPTION 1; EXTRA FUEL SAVINGS .FROM USS OF THE TWO-SPEED IDLE TEST OR
LOADED TEST ON 1981 ANT) LATER VEHICLES
The use of either the Two-Speed Idle Test or the Loaded Test[4] for 1981 and
later vehicle results in an identification rate of 70% [3] of the fuel system
failures mentioned in Section 2.2.3 versus the 50? rate for the simple idle
test.
The Tvo-Speed Idle Test consists of vehicle operation at 2500 rpm (in neutral
gear) as well as at normal idle. The Loaded Test consists of vehicle
operation at constant 30 mph with a dynamometer load of 9.0 hp, as well as at
nornal idle. The 70% identification rate assumes that cutpoints of 1.2% CO
and 220 ppm EC are applied at both speeds for either test and that vehicles
must pass both pollutant cutpoints at both speeds to pass the I/M test.
The average benefits for 1981 and later vehicles using either of these two
tests are given for each calendar year in Table 9. These benefits for 1981
and later vehicles were calculated in the manner described in Section 2.3.1.
Table 9 also shows the incremental benefit relative to the basic benefits for
these vehicles shown in Table 4.
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Table 9
I/M Fuel Economy Benefit for 1981 and Later Vehicles
Using the Two-Speed Idle Test or Loaded Test
Calendar Fleet Incremental Benefit
Year Benefit Re la t ive t o Id le Te st
1983 .55% .13%
1984 .75% .21%
1985 .97% .33%
1986 1.07% .29%
1987 1.22% .36%
The incremental benfit for 1981 and later vehicles from Table 9 for each
caler.dar year was applied to the fuel consumption of all 1981 and later
vehicles in that calendar year. The resulting fuel savings in gallons and
dollars were converted to a fleetwide basis by averaging the benefits for 1981
and later vehicles with the zero benefits for the pre-1981 vehicles. This
calculation followed the steps described in more detail in Sections 2.3.2 and
2.3.3 and the Appendix. The results of the calculation are the incremental
annual fuel savings (averaged over five years) per inspected vehicle due to
the use of the Two-Speed Idle Test or Loaded Test instead of the Idle Test
used in the basic I/M program. These incremental benefits are shown in Table
10. Table 10 also shows the incremental nationwide fuel savings in gallons,
calculated as described in Section 2.3.6.
Table 10
Incremental I/M Annual Fuel Savings Per Inspected
Vehicle from Using the Two-Speed Idle Test or Loaded Test
Nationwide
Gallons Saved
Dollar Savings Fuel Savings (Millions)
SI.11 0.12% 33.8
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4.0 OPTION 2: EXTRA FUEL SAVINGS FROM MECHANIC TRAINING
The incremental fuel savings achievable through a formal mechanic training
program will depend on the type of repair approach used in the I/M area. The
fuel economy benefit for a pre-1981 vehicle which fails I/M and is repaired by
a mechanic who has received formal training is estimated to be 0.8% for
conventional training programs. Although training results in mechanics
performing certain types of repairs which improve fuel economy, other, repair
practices which may degrade fuel economy remain. However, there is the net
beneficial effect of 0.8% which is not seen without, training. For I/M
programs and training programs which result in repairs consisting of only
carburetor adjustments (and other types of repairs which do not degrade fuel
economy), the fuel economy benefit has been shown to be 4% per failed vehicle.
These mechanic training benefits for pre-1981 repaired vehicles are based on
data from EPA studies. The benefit of 0.8% is taken from two sources: a
mechanic training study in Portland[5] and an analysis of vehicles with I/M
repairs which did not have their ignition timing settings grossly maladjusted
in the "retarded" directionfo]. The latter analysis is relevant in estimating
mechanic training benefits, because proper ignition timing adjustment is an
important aspect of mechanic training. The two sources both yielded a benefit
of 0.8% for failed vehicles.
The benefit of 4% for failed vehicles receiving only carburetor adjustments is
based mainly on an EPA study in Houston in which contractor personnel repaired
vehicles by adjusting the carburetors simply to a specific idle CO level[8],
This is a practical and realistic approach which yields full CO emission
reduction benefits and partial, but substantial, HC emission reduction
benefits. This approach may not require extensive mechanic training; a very
brief training course and/or an enforcement mechanism to assure that the
vehicles are set to the proper idle CO level and to discourage or eliminate
repair practices which degrade fuel economy may be all that is necessary.
Further details of this approach may be found in Reference 9. Several other
EPA studies confirmed the ability of repairs to result in a 4% improvement
[1,5,7], Repairs were often extensive in these latter programs, however
carburetor adjustments were the most common repairs performed and were
responsible for most of the fuel economy benefit. The figure of 4% appeared
repeatedly in these programs.
No deterioration of the above fuel economy benefits between inspections Is
anticipated. This conclusion was reached from an analysis of vehicles which
were tested quarterly for a period of one year after they received repairs to
pass the I/M test in Portland. Data from 93 repaired vehicles which had a
mean fuel economy increase due to maintenance showed no loss in fuel economy
during the following year. The fuel economy was very stable and level
throughout the time period[10].
A typical failure rate for pre-1981 vehicles, and the one used in this
analysis, is 20%. Thus, the fuel economy benefits averaged over all the
pre-1981 I/M vehicles are 0.16% and 0.8%, -respectively, for the 0.8% and 4%
cases described above.
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To determine average savings for pre-1981 vehicles due to mechanic training In
each year and over the five year period the same method was used as for the
basic program benefits. The consumption in gallons of all pre-1981 vehicles
without I/M was calculated first and then th,e benefits applied, once for each
estimate.
No additional fuel economy benefit from mechanic training over the basic
benefit is expected for 1981 and later vehicles. This is because even without
training, mechanics must correctly and fully repair these vehicles' fuel
systems in order for them to pass the I/M reinspection.
Table 11 shows the incremental fuel savings (averaged over five years) from
mechanic training. The high end of the range of savings is based on the 4%
benefit for failed vehicles receiving only carburetor adjustments and is
available in I/M programs which, achieve this type of repair through training
or some other means.
Table 11
Incremental I/M Annual Fuel Savings per Inspected
Vehicle from Mechanic Training
Nationwide
Gallons Saved
Dollar Savings Fuel Sayings (Millions)
$0.83-^4.18 0.09-0.46% 26.2-130.2
5.0 OPTION 3: FUEL SAVINGS FROM TIRE PRESSURE CHECKS AT I/M STATIONS
Fuel econoray benefits from I/M are usually thought of as being associated with
engine tune-ups. However, large benefits can also come from proper tire
inflation. An inspection program is a good opportunity to achieve this
potential benefit. .
Tire rolling resistance is greatly increased when the tire pressure is lower
than optimum. The lower the pressure the greater the amount of bending in the
tire that takes place, taking more energy and therefore fuel. Each one
pound—per-square-inch loss in tire inflation pressure reduces fuel economy by
three-tenths of one percent[ll]. . '
Two assumptions used in this analysis are that the current average in-use tire
pressure is 24.8 psi, which is 1.8 psi below the average pressure specifi-
cation, and that this discrepancy will remain constant in the future in the
absence of I/M pressure checks. These values come from pressure measurements
of nearly 2000 vehicles in recent EPA test programs[12]. Another assumption
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is that tires deflate at an average rate of 1.0 psi per month between checks
and will continue to do so.* The latter assumption is based on a consensus of
conversations with industry, but no specific studies.
Minimum Benefit Scenario - The minimum benefit scenario calls for an increase
to a "cold" inflation pressure of 28 psi of all tires which are found to be
below that during the I/M test. (A "cold" inflation pressure is the pressure
the tire would have at ambient temperature.) Because some tires will be
higher than 28 psi when checked at the I/M lane and will be left that way, the.
fleet average tire pressure immediately after inspection becomes 28.4 psi.
This is far below the maximum pressure recommended on the sidewall of the
tires and should have no effect on ride quality. The result of this is a 3.6
psi increase over the present average which would yield a 1.08% fuel economy
increase if no deterioration occurred.
To calculate deterioration, it is assumed that owners will fill their tires
every three months, but that they will only fill the tires to an average of 27
psi for two reasons: (1) out of habit, some owners will fill the tires to the
lower pressures to which they are accustomed; (2) some tires will be filled
when warm, which results in a lower equivalent cold inflation pressure. The
average lower fill pressure coupled with deterioration results in a yearly
tire pressure average of just 1.0 psi higher than the current level,
representing a 0.3% fuel economy benefit.
Maximum Benefit Scenario - The maximum-benefit scenario calls for an increase
to a cold inflation pressure .of 32 psi of all tires found to be below that
during the I/M test. This pressure is generally the maximum inflation
pressure for current tires recommended by the tire manufacturers and should be
considered perfectly safe. (The Tennessee Valley Authority has successfully
used the maximum tire manufacturer recommended pressures on its vehicles for
many years and reports no safety problems.) It is possible, however, that
this could cause ride harshness in some vehicles and possible adverse handling
effects on some older vehicles with large differences in recommended front and
rear pressures such as older VW Beetles. The exclusion of such vehicles may-
be appropriate, therefore, but because of the relatively small number of
vehicles excluded, the fuel economy benefits are not expected to be noticeably
reduced.
The fleet average tire pressure immediately after inspection becomes 32.1 psi
as a result of this program. Without deterioration this would translate to a
2.19% fuel economy increase. It is assumed that a good public awareness
program is mounted and that this will help maintain tire pressures between the
annual I/M tests. For example, leaflets could be handed out at the I/M
station explaining the importance of frequent checks and high pressures. In
this case it is assumed that owners will fill their tires every two months on
* It is interesting to note that with these average values for in-use
pressure, specifications, and deflation rate, the "average tire" appears to be
checked and reinflated to its specified pressure once every 3.6 months.
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the average and that they fill them to an average of 31 psl (cold). Over a
or.e year period the average tire .pressure would then be 30.2 psi which is 5.4
psi over the present average, resulting in a 1.62% fuel sconce:y increase
(1.59% fuel consumption benefit) for the fleet.
The percentage benefit of each scenario is applied to the base fusl consump-
tion of the entire fleet of vehicles, since the checks will be performed on
all inspected vehicles. Table 12 shows the incremental fuel savings (averaged
over five years) from the two tire pressure check scenarios.
Table 12
Incremental I/M Annual Fuel Savings per Inspected
Vehicle from Tire Pressure Checks
Scenario
Minimum Benefit
Maximum Benefit
Dollar
Savings
£ 2.74
$14.88
Fuel
Savings
0.30%
1.59%
Nationwide Gallons
Saved (Millions)
84.8
453.8
6.0 SUMMARY OF OPTIONS AND THE OPTIMAL PROGRAM
This section consolidates the results for the basic I/M program and for the
three options for increasing the fuel savings from I/M, and presents the fuel
savings from an optimal program.
Table 13 shows the combined incremental fuel savings from the three options.
The mechanic training option is shown as having a range of benefits. The low
end of this range is achievable in any I/M program by implementing a
conventional training program; the high end of the range is achievable only if
repairs consist only of carburetor adjustments (and other repairs that can be
expected not to degrade fuel economy), a situation that may be achieved by
special forms of training and/or an appropriate enforcement mechanism.
The tire pressure check option is also shown as having a range of benefits.
The low end of this range is based on a minimum benefit scenario which should
be reproducible in any I/M program. The high end of the range can be achieved
only if the optimal tire pressure for fuel economy — 32 psi — is used in the
I/M stations and if the public awareness campaign is adequate to motivate
owners to check and inflate their own tires to within one psi of this pressure
every other month.
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Table 13
Annual Fuel Economy Benefits for
Inspected Vehicles Due to,I/M Options
Option
Dollar
Savings
Fuel
Savings
Nationwide
Gallons Saved
(Millions)
(1) More Effective Test !/
for 1981 and Later Cars
(2) Mechanic Training "L>
(3) Tire Pressure Checks
$1.11
0.12%
$0.83- §4.18 0.09- 0.46%
$2.74- $14.88 0.30- 1.59%
33.8
26.2-130.2
84.8-453.8
All Options Combined
£4.68- £20.17 0.51- 2.17%
144.8-617.8
\j Average annual benefits for the five year period 1983 through 1987. 1980
dollars.
2J Two-Speed Idle Test or Loaded Test.
3/ The maximum benefit shown is only available for a specific type of repair
approach. See Section 4.0 and Reference 9.
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An optimal I/M program would incorporate all three options in addition to the
basic I/M program. For the two options which have a range of possible
benefits, the forn of the option with the highest fuel economy benefit would
be implemented. Specifically, the optimal I/M program for fuel savings
(1) uses the Two-Speed Idle Test or the Loaded Test for inspecting 1981
and later vehicles,
(2) includes a mechanic training program and/or an enforcement mechanism
which has the effect of eliminating repair practices which degrade fuel
economy, leaving only carburetor adjustments— which cause a 4% improve-
ment in fuel economy — and other repairs which can be expected not to
degrade fuel economy, and
(3) checks the pressure of each tire on each vehicle receiving an I/M
test, inflates those which are below 32 psi (cold) to 32 psi, and
successfully encourages vehicle owners to do the same themselves (within
one psi) every other month.
The fuel economy benefits of this optimal I/M program are shown in Table-14.
Table 14
Annual Fuel Economy Benefits Per Inspected
Vehicle From the Optimal I/M Program !/
Components of the Dollar Fuel Nationwide Gallons
Optimal I/M Program Savings Savings Saved (Millions) .
Basic I/M Program $ 2.74 0.29% 83.6
More Effective Test $ 1.11 0.12% 33.8
Mechanic Training $ 4.18 0.46% 130.2
Tire Pressure Checks $14.88 1.59% 453.8
Total for Optimal Program $22.91 2.46% . 701.4
\J Average annual benefits for the five year period 1983 through 1987. 1980
dollars. . .
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18
Rererence s
i. "Effects of Inspection and Maintenance Programs on Fuel Economy,"
IMS-Q01/FE-1, I/M Staff, EPA, March 1979.
2. "Achieving Fuel Economy Benefits from Motor Vehicle Inspection Programs,"
presentation to Eighth Annual North American Motor Vehicle Emissions
Control Conference by Phil Lorang, I/M Staff, EPA, September 30, 1980.
3. "Fuel Economy Benefits From I/M for 1981 and Later Model Year Vehicles",
nemo from Dave Hughes to Tom Cackette, EPA I/M Staff, January 22, 1981.
4. "Motor Vehicles; Emission Control System Performance Warranty Short
Tests", Federal Register, Vol. 45, No. 101, May 22, 1980, pp. 34804-5.
5. "A Study of the Effectiveness of Mechanic Training For Vehicle Emissions
Inspection and Maintenance Programs", EPA Technical Report, I/M Staff by
R. Bruce Michael, April 1981. -
6. "Simulation of I/M Fuel Economy Benefits Due to Adding Ignition Timing
Cutpoints to the Basic Idle Emissions Test", memo from R. Bruce Michael
and Jim Rutherford., SPA I/M Staff, to Charles Gray, Emission Control
Technology Division, May 12, 1980.
7. "Emission Reductions from RM Vehicles Compared with the Portland I/M
Program," memo from R. Bruce Michael to Tom Cackette, EPA I/M Staff,
March 15, 1979.
8. Letter to Joe Seliber of the City of Chicago, from David Brzezinski, EPA
, I/M Staff, January 19, 1981.
9. "Low Cost Approaches to Vehicle Inspection and Maintenance", EPA Technical
Report EPA-AA-IMS/81-7, I/M Staff, April 1981.
10. "Deterioration of Fuel Economy Benefits in I/M Programs," memo from
R. Bruce Michael to Tom Cackette, EPA I/M Staff, March 13, 1981.
11. "The Effects of Tire Inflation Pressure on Passenger Car Fuel Consump-
tion," SAE paper #810068, Thompson, Reinimann and Grugett, February 1981.
12. "The Effect of Tire Inflation Pressure on Vehicle Fuel Economy,"
EPA-AA SDSE-80-04, Bruce Grugett, April 1980.
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19
APPENDIX
METHODOLOGY FOR REPORT
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20
APPENDIX - METHODOLOGY FOR REPORT
1.0 INTRODUCTION
The information in Table 1 of the report was derived from the calculation of
fuel consumed for each calendar year studied. Savings, both in terms of
gallons saved and dollars saved are based on this.
As mentioned in Section 1.2 of the report, it is necessary to make calcula-
tions for each model year (MYR) of vehicles for each calendar year studied due
to several factors which vary by year. For example, since the average vehicle
miles traveled of a MYR varies with time and the average miles per gallon
(mpg) achieved by that MYR is unique, the gasoline consumption of the MYR
changes every calendar year and is independent of every other MYR.
There are five basic facts needed in order to calculate each MYR's basic
(non-I/M) fuel consumption for a given calendar year. Once this is calcu-
lated, the savings due to I/M and the options are applied, and all MYR's
summed. The five items needed are:
0 Registration fraction of all passenger cars contributed by the KYR
0 Average miles traveled by the MYR
0 Fraction of diesel cars in each MYR
0 The total U.S. VMT for all passenger cars for the calendar year
0 Average mpg of each MYR
Details of the calculations for each of these five are presented in Section
2.0 of the Appendix. Also presented are the calendar year fleet sizes, which
are necessary in determining the savings per vehicle.
2.0 DATA NECESSARY FOR .FINAL CALCULATIONS OF FUEL CONSUMPTION
2.1 Registration Fractions of Each MYR
These fractions relate to numbers of vehicles and are necessary in determining
fuel consumption of the MYR. The fractions vary for each MYR over time,
getting smaller due to vehicles retiring from service.
EPA's standard estimates of the national distribution were used. These are
based on historical patterns and are available in such papers as Automotive
News. The data had to be modified for a January 1 date (instead of the July 1
date usually found, since this report assumes the I/M program begins on
January 1). The estimate assumes that the fractions stay constant throughout
the calendar years studied. For .example, the fraction for the first model
year index, .025, applies to the 1983 MYR in 1983, the 1984 MYR in 1984, etc.
Table A-l presents the registration fractions in the order of' newest to oldest
vehicles. Note that the fraction for the first year is small, because on
January 1 of any year only about one-fourth of that model year has been sold
(vehicles usually go on sale in October of the preceding year). For example,
on January 1, 1983, the first model year index represents the 1983 model year,
part of which has already been sold. . .
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21
2.2 Average Miles Traveled for Each MYR in the Preceeding.12 Months
Consumption is dependent on the distance traveled. EPA estimates were used
and were again based on historical patterns. The analysis assumes that the
travel rates stay constant through the calendar years studied, e.g. vehicles
one year old are always driven the same amount, on the. average. The mileage
accumulations are presented in Table A—I. The first year's accumulation is
very low, because these vehicles have been driven at most three months out of
the last year. The second year accumulation is also fairly low, because about
three-fourths of the vehicles in this group have been driven less than one
year.
Table A-l
Automobile Registrations and Mileage Accumulation Rates
Model Year
Index
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20+
Registration
Fraction
Mileage Accumulation
During Previous 12 Months
1800
8984
14025
13522
12953
12425
11922
11353
10825
10322
9353
9225
8722
8153
7625
7122
6553
6025
5525
5022
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22
2.3 Fraction of Diesel Cars in Each NYR
Since diesel cars are not inspected in the typical I/M program used in this
report, they have to be subtracted from ,the total number of light-duty
vehicles. Otherwise, savings due to I/M and the options would be incorrectly
applied to these vehicles and the national fuel savings would be overstated.
EPA estimates of diesel sales fractions are applied. Table A-2 presents the
estimates by model year. For ease of calculation of the total consuaption,
the gasoline car sales fraction is shown, not the diesel car fraction. The
percentages are less than 100% back to 1975 only, since diesels do not
contribute a noticeable sales fraction earlier than that.
2.4 Average Miles Per Gallon (HPG) of Each MYR
The fuel economy (inpg) is needed for each MYR in order to calculate . the fuel
consumed. For 1979 and earlier MYRs the estimates are based on in-use
testing. These results yield lower numbers than EPA new car certification
calculations and DOE fuel economy standards. The comparison of in-use data to
certification data shows a substantial shortfall in fuel economy. The
analysis of this shortfall was used to forecast future MYRs1 fuel economies;
this is possible because the certification design fuel economies can be
accurately estimated from the new car fuel economy standards.* The fuel
economies are shown in Table A-2.
* "Passenger Car Fuel Economy: EPA and Road," EPA 460/3-80-010, August, 1980.
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23
Table A-2
Gasoline Powered Vehicle Sales Fractions and Average
Fuel Economy By Model Year
Gasoline Car Fuel Economy
Model year Sales Fraction (mpg) *
1988 .824 21.7
1987 .835 21.5
1986 .862 21.3
1985 .886 21.1
1984 .905 20.8
1983 .911 20.6
1982 .925 19.8
1981 .953 19.0
1980 .966 18.1
1979 .972 16.87
1978 .991 15.81
1977 .995 14.72
1976 .997 14.11
1975 .998 13.83
1974 1 13.23
1973 1 13.19
1972 1 13.40
1971 1 13.33
1969 1 13.56
1968 1 13.53
1967 & earlier 1 13.53
* From "Passenger Fuel Economy: EPA and Road", EPA 460/3-80-010, August 1980.
Values for the 1986-88 model years were extrapolated, since this reference
gives estimates only through the 1985 model year.
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24
2.5 Fleet Size and Total Vehicle Miles Traveled (VMT) of All Passenger Cars
The VMT of each model year needs to be calculated in order, to detemine
gallons of fuel consumed by that model year. The fleet size (total number of
passenger cars in the U.S.) is needed only after ths consumption calculations
to determine the savings per vehicle.
The fleet sizes for each of the study years was based on Federal Highways
Administration (FHA) data for 1979 and an average growth rate of 1.6% based on
projections in a Department of Energy paper for the Society of Automotive
Engineers (SAE 790226). Likewise, the VMT for all passenger cars was based on
FHA data for 1979 and a growth rate of 1.4% frota DOE projections. The
estimated fleet size arid VMT are presented in Table A-3.
Table A-3
National Passenger Car Fleet Size and VMT By
Calendar Year
Calendar Passenger Passenger Car
Year Car Fleet Size VMT (Billion)
1987 138.7 1292.5
1986 136.5 1274.7
1985 134.4 1257.1
1984 132.3 1239.7
1983 130.2 1222.6
3.0 FUEL CONSUMPTION CALCULATION
Data from the preceding sections can be used to calculate the travel fraction
of each model year of gasoline powered cars during each calendar year. Each
fraction is then multiplied by the total VMT for that calendar year and
divided by the average fuel economy of the vehicles of that model year to
yield gallons consumed. The fuel economy benefits (alternatively, the fuel
consumption reductions) are applied to each year and then the sum is calcu-
lated to yield a single fuel economy benefit for the whole fleet.
A particular situation had to be accounted for in the calculations. In any
given calendar year, none of the vehicles of the first model year and only
one-fourth of the vehicles of the second model year are subject to I/M. For
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25
example, on January 1, 1984 all of the 1984 model year vehicles which have
bean sold and about three-fourths of the 1983 model years (the cnes less than
one year old) would not have been inspected. This is due to the assumption
that vehicles will not be tested until they are one year old. Benefits were
therefore not applied to these vehicles.
Another situation was also accounted for. The one-fourth of the vehicles of
the second MYR which are inspected have been in service a full year and
therefore have traveled a.farther average distance than is depicted in Table
A-l. The mileage accumulation for the third index .year was applied to these
vehicles to calculate their consumption. This resulted in using the equiva-
lent of 39% of the miles traveled by the entire second MYR instead of just 25%.
4.0 CALCULATION OF BENEFITS
There are six benefits which can be considered: low and high situations each
for the basic I/M program, a mechanic training program, and tire pressure
checks. The first four of these have to be applied differently according to
whether the vehicles are 1981 and later, or pre-1981. Therefore, it is
simplest to calculate the base consumption for the 1981 and .later fleet and
the pre-1981 fleet separately, and then apply the benefits accordingly.
Benefits were always applied to the base case (non-I/M) consumption rather
than to the consumption with another option. For example, the tire pressure
check benefits were applied to the consumption of the base case rather than to
the consumption with the I/M program and mechanic training. In this way the
options can be kept separate. The calculation for tire pressure check
benefits is slightly incorrect due to this, because the benefits are applied
to the base case of slightly higher consumption than the I/M case. Applying
the benefits to the basic I/M program consumption, whigh is slightly lower,
shows an indetectable difference, however. The mechanic training options
yield entirely correct results when applied in this manner. This is because
mechanic training only has benefits on pre-1981 vehicles and the consumption
for these vehicles is the same whether with or without the basic I/M program.
The benefits associated with each option and calendar year are summarized in
Table A-4.
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26
Table A-4
I/M Fuel Economy Benefits
- - - - Fleet Percent Fuel. Savings - - - -
Calendar
Year
1983
1984
1985
1986
1987
Models
Covered
1968-80
1981-later
1968-80
1981-later
1968-80
1981-later
1968-80
1981-later
1968-80
1981-later
Basic
Program
(Idle
Test)
0
.42
0
.54
0
.64
0
.78
0
.86
Mechanic Training
More
Effective
Test *
0
.55
0
•75
0
.97
0
1.07
0
1.22
Conventional
.. Programs
.16
0
.16
0
.16
0
.16
0
.16
0
Carburetor
Tire
Adjustments Pressure
Only
.80
0
.80
0
.80
0
.80
0
.80
0
MIN
.30
.30
.30
.30
.30
.30
.30
.30
.30
.30
MAX
1.62
1.62
1.62
1.62
1.62
1.62
1.62
. 1.62
1.62
1.62
Two-Speed Idle Test or Loaded Test on 1981 and Later Vehicles
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27
5.0 SAMPLE CALCULATION
A sample calculation for the 1987 calendar year will be explained.
The first step is to determine the registration percentage of gasoline
vehicles in each model year. This is accomplished by multiplying the
registration fraction in Table A-l by the gasoline car sales fraction in Table
A-2, for each model year. This yields gasoline vehicle registration fractions
(RF). (The summation of these yields the fraction of all passenger cars which
are gasoline powered, .922 in the sample case in Table A-5, which is needed
for a lat.er step.) These fractions are multiplied by the corresponding
mileage accumulations of Table A-l to yield what can be called "registration
fraction miles traveled" (FMT). The summation of the FMT is needed for the
following calculation. The next step determines the gasoline vehicle travel
fractions, i.e., the fraction of all miles traveled by the gasoline powered
vehicles of each model year. This is obtained by multiplying each FMT by the
sum of the RF (to account for the fact that the gasoline vehicles do not
travel all of the miles) and dividing by the sum of the FMT.
At this point we have the travel fractions of all of the gasoline powered
vehicles, but these need to be modified before we can calculate the consump-
tions. This is because not all of the vehicles are subject to inspection.
The next step, therefore, is to determine the travel fractions of only the I/M
vehicles. None of the latest MYR, only a portion of the second latest MYR and
no vehicles earlier than the 1968 MYR will be inspected. Therefore, all of
the travel fractions for those MYR's will be changed to zero, except for the
second MYR. As explained in Section 3.0 of this Appendix, this latter
fraction becomes approximately 39% of its original value.
The final step in determining the base fuel consumption of each MYR of
vehicles subject to I/M is to multiply the resultant travel fractions by the
VMT of all vehicles in I/M areas (45% of total U.S. VMT) and divide by the
appropriate miles-per-galion figure for the MYR. These numbers can then be
summed into two groups, one for the 1981 and later vehicles, and another for
the pre-1931's. The reason for doing this is that all of the I/M benefits,
except tire pressure checks, are dependent on these categories. The next
series of steps is simply to apply the estimated option savings to the base
fuel consumptions to determine the gallons saved. When all of these are
calculated, the savings per vehicle can be calculated by dividing the gallons
saved by the number of vehicles subject to I/M and then applying the estimated
price per gallon of gas. Calculations are shown for the 1987 calendar year in
Table A-5.
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28
Table A-5
SaiHple Calculation for Calendar Year 1987
Toual VMT of all U.S. passenger cars = 1274.7 billion miles
Total passenger cars in U.S. = 136.5 million
Price per gallon of gasoline in 1980 dollars = $1.70 per gallon
MYx
I9c3
87
86
85
84
83
82
81
(A)
Registr.
Fraction
.025
.106
.096
.074
.096
.108
.093
.074
(B)
Gasoline
Vehicle
Sales
Fraction
.824
.835
.862
.886
.905
.911
.925
.953
(A*B)
Gasoline
Vehicle
Registr.
.0206
.0885
.0828
.0656
.0869
.0983
.0860
.0705
(C)
Mileage
Accum.
1800
8984
14,025
13,522
12,953
12,425
11,922
11,353
(A*B*C*)
FMT
37.1
795.1
1161.3
887.0
1125.6
1221.4
1025.3
800.4
(A*8*C*)*
(.922)
(10,004.1)
Travel
Fractions
.003
.073
.107
.082
.104
.113
.095
.074
Modified
Travel
Fractions
0
.028
.107
.082
.104
.113
.095
.074
Fuel
Economy
mpg
. __
21.5
21.3
21.1
20.8
20.6
19.8
19.0
Base
Consumption •
0.747
.2.882
2.229
2.868
3.147
2.752
2.234
Subtotal 16.859
80
79
78
77
76
75
74
73
72
71
70
69
68
67-
.069
.062
.050
.037
.031
.024
.016
.011
.006
.004
.002
.002
.001
.013
1.000
.966
.972
.991
.995
.997
.998
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
.0667
.0603
.0496
.0368
.0309
.0240
.016
.011
.006
.004
.002
.002
.001
.013
.922
10,825
10,322
9353
9225
8722
8153
7625
7122
6553
6025
5525
5022
4500
4500
722.0
622.4
454.0
339.5
269.5
195.7
122.0
78.3
39.3
24.1
11.1
10.0
4.5
58.5
10,004.1
.067
.057
.042
.031
.025
.018
.011
.007
.004
.002
.001
.001
.0004
.005
.922
.067
.057
.042
.031
.025
.018
.011
.007
.004
.002
.001
.001
.0004
0
.869
18.1
16.87
15.81
14.72
14.11
13.83
13.23
13.19
13.40 .
13.33
13.63
13.56
13.53
-
2.123
1.938
1.524
1.208
1.016
0.747
0.477
0.304
0.171
0.086
0.042
0.042
0.017
Subtotal 9.696
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29
Table A-5 (continued)
Sample Calculation for Calendar Year 1987
Fuel Savings in Billion Gallons During 1987 from Basic I/M Program and Each Option
(Using Percent Savings from Table A-4)
Mechanic Tra.ining Tire Pressures
Base Basic I/M More Effective Carburetor
(No-I/M) Program Test for Adjustments
VVR Consumption (Idle Test) 1981 and Later Conventional . Only MIN MAX
1961 and •
Liter
Pre-1961
16.859
9.696
0.144
0.0
0.203
0.0
0.0
0.015
0.0
0.077
0.050
0.029
0.269
0.155
TOTAL 26.555 0.144 0.203 0.015 0.077 0.079 0.424
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