EPA-AA-SDSB 79-24
Technical Report
Average Lifetime Periods for
Light-Duty Trucks and
Heavy-Duty Vehicles
by
Glenn W. Passavant
November 1979
Notice
Technical Reports do not necessarily represent final EPA decisions or
positions. They are intended to present technical analysis of issues
using data'which are currently available. The purpose in the release of
such reports is to facilitate the exchange of technical information and
to inform the public of technical developments which may form the basis
for a final EPA decision, position or regulatory action.
Standards Development and Support Branch
Emission Control Technology Division
Office of Mobile Source Air Pollution Control
Office of Air, Noise and Radiation
U.S. Environmental Protection Agency
-------
-1-
Table of Contents page
I Foreword 1
II Summary 1
III Background 2
IV Determination of the Average Lifetime Periods 2
a. Methodology 2
b. Scrappage Rates 3
c. Average Mileage Accumulation Rates 3
d. Calculations 11
e. Discussion and Conclusions 20
-------
-2—
I. Foreword
An accurate estimate of the average lifetime period for any enis-
sions source is an essential factor in determining the lifetime opera-
ting costs and emissions reductions which can be expected in any eais-
sion control strategy.
The Clean Air Act Amendments of 1977 mandate the U.S. Environmental
Protection Agency to further control emissions from light-duty trucks
and heavy-duty engines.
This technical report uses published vehicle scrappage and mileage
accumulation data to estimate average lifetime periods for light-duty
trucks and heavy-duty engines. These lifetime periods can be used in
the air quality, economic impact, and cost effectiveness-analyses assoc-
iated with the pending and upcoming rulemaking actions affecting light-
duty trucks and heavy-duty engines.
II. Summary
This technical report estimates average lifetime periods for light-
duty trucks and heavy—duty vehicles.
The average lifetime in miles and years for any vehicle in either
of these two classes was estimated using scrappage rate data and mileage
accumulation data. These data were then used in a simple statistical
procedure to estimate average lifetime periods at:
Light-duty trucks (£ 6,000 Ibs. GVWR) 122,000 miles/12 years
Light-duty trucks (6-8,500 Ibs. GVWR) 119,000 miles/12 years
Composite LDT class (0-8,500 Ibs. GVWR) 120,000 niles/12 years
Heavy-duty gasoline-fueled vehicles 114,000 miles/8 years
(>8,500 Ibs. GVWR)
Heavy-duty diesel vehicles 475,000 railes/9 years
(>8,500 Ibs. GVWR)
These lifetime periods can be used in the regulatory analyses asso-
ciated with the upcoming light-duty trucks and heavy-duty vehicle/engine
rulemaking actions.
-------
-3-
III. Background:
The EPA is nox* involved in the preparation/promulgation of several
rulemaking packages involving light-duty trucks and heavy-duty engines.
The average lifetime periods of these vehicles/engines (hereafter .
referred to as vehicles only) in both miles and years is an. essential
input in determining the environmental impact, cost, and cost effective-
ness of these rulemaking packages. The average lifetime in miles is
used to compute the emissions decrease per vehicle and is also necessary
to determine changes in operating costs which are a function of mileage.
The average lifetime in years is used to compute operating costs which
are functions of time. The cost effectiveness is then computed from
these cost and benefit figures.
The average lifetime period as defined in this report is the length
of time and/or number of miles an average vehicle is in use. Using the
term average implies that some vehicles will have lifetime periods less
than the "average" and some will have lifetime periods greater. How-
ever, the average lifetime is an effective means of representing the
usage pattern for a large fleet of light-duty trucks or heavy-duty
vehicles.
IV. Determination of the Average Lifetime Periods
A. Methodology
The average lifetime miles of a fleet of vehicles produced in the
same year can be expressed by the formula:
n
ALM = I f .m.
1-1 X X
where:
ALM = average lifetime miles
i = vehicle/engine age.
n = age at which last vehicle/engine of a fleet is scrapped.
f. = fraction of vehicles/engines which are scrapped
at age i.
m. = average cumulative mileage on vehicles which are
scrapped at age i.
Therefore, if the scrappage and average mileage accumulation rates
for a fleet of vehicles are known, the average lifetime mileage and
period can be determined.
-------
B. Scrappage Rates
The scrappage rates used in this report were taken from a report
prepared by Michigan Technological University under contract to EPA._l/2/
The scrappage rates were computed by contrasting known factory sales, as
they appear in MVMA publications, with corresponding model year stock of
vehicles estimated from the 1972 Census of Transportation. For example,
to compute the cumulative scrappage rate at 9 years for vehicles pro-
duced in 1970 the method xrould simply be:
Total 1970 sales - 1979 registrations of 1970 vehicles
Total 1970 sales
This methodology can then be applied to different classes of vehicles
for different years and the cumulative scrappage rates can be computed.
To overcome some data acquisition and application problems cumula-
tive scrappage rates were computed for only three major categories:
(Light-Duty Trucks: Gas and Diesel) (0-10,000 Ib GVWR), HD Gasoline
(HDG) (>10,000 Ib GVWR) and HD Diesel (HDD) (>10,000 Ib GVWR). These
cumulative scrappage rates are shown in Table 1 and Figure 1. The
annual scrappage rates also shown in Table 1 were computed by sub-
tracting the cumulative scrappage rates.
C. Average Mileage Accumulation Rates
After examining several mileage accumulation rates models the data
presented in the current mobile source emission factors document was
selected because the vehicle classes were the same as the primary EPA
Vehicle classes.^/ It contains mileage accumulation data covering a
twenty year period for four major vehicle classes:
LLDT - light-duty trucks: <6,000 Ibs GVWR
HLDT - light-duty trucks: 6,001-8,500 Ibs GVWR
HDG - gasoline-fueled heavy-duty vehicles: >8,500 Ibs GVWR
HDD - diesel heavy-duty vehicles: >8,500 Ibs GVWR
2_/"The Development of an Emission and Fuel Economy Computer Model for
Heavy-Duty Trucks and Buses," John H. Johnson and Anil B. Jarabekar,
August 1977, EPA-R803782010.
2/Tlhis is also available from the Society of Automotive Engineers - SAE
Paper 780630.
3/Mobile Source Emission Factors EPA-400/9-78-055, March 1978.
-------
— 5—
Table 1
Scrappage Rates
Years
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
LDT
.00
.03
.04
.05
.05
.05
.05
.05
.05
.04
.04
.04
.04
.04
.03
.04
.04
.04
.03
.04
.03
.03
.03
.02
.02
.02
.01
.01
.02
.02
.00
.03
.07
.12
.17
.22
.27
.32
.37
.41
.45
.49
.53
.57
.60
.64
.68
.72
.75
.79
.82
.85
.88
.90
.92
.94
.95
.96
.98
1.0
A'
.00
.05
.07
.09
.10
.08
.07
.06
.05
.05
.05
.04
.04
.05
.03
.03
.03
.03
.02
.02
.01
.01
.01
.01
-
-
-
HDG
C
.00
.05
.12
.21
.31
.39
.46
.52
.57
.62
.67
.71
.75
.80
.83
.86
.89
.92
.94
.96
.97
.98
.99
1.0
A
.00
.09
.07
.07
.06
.07
.06
:.05
.05
.05
.04
.04
.04
.03
.04
.03
.02
.03
.02
.03
.02
.02
.02
.02
.01
.01
.01
HDD
C
.00
.09
.16
.23
.29
.36
.42
.47
.52
.57
.61
.65
.69
.72
.76
.79
.81
.84
.86
.89
.91
.93
.95
.97
.98
.99
1.0
LDT: All trucks less than 10,000 Ib GVW: Classes 1 and 2
Gasoline trucks above 10,000 Ib GVW: Classes 3-8
Diesel trucks above 10,000 Ib GVW: Classes 3-8
HDG:V
HDD:
A - annual
C - cumulative
-------
o
Ul
a.
a.
oo
:z
OTd
a:
o
3
.3
VEHICLE SCRRPPRGE
( X=LDT 'T=HDG Z=HDD
5.00
7.00 ..
9.00
1I.CO
13.00
15.00 17.00
YEflRS
18.00
SUM
23JO
25.00
29.00
3UOO
FIGURE 1
-------
To make the mileage accumulation rate model given in the emission
factors document directly applicable in computing average lifetime
periods three ^adjustments -to: the .-.data were necessary.
The first adjustment involved extending the mileage accumulation
rate data to cover the same, number of years as the scrappage rate data.
This extension covered 10 years for LLDT and HLDT, 4 years for HDG and
7 years for HDD. This extension was accomplished using the "Fraction
Reduction in Vehicle Miles Traveled with Age" data found in the Johnson
and Jambekar report, and assuming (1) that LDTs are classes 1 and 2, (2)
most HDG vehicles are class 6 and most HDD vehicles are classes 7, 8 and
(3) the fraction reduction decreases a small amount each year after
eighteen years.
The data actually used in this extension is found in Table 2. The
manner in which this data.was used is shown in the example below:
HDG Vehicles
Year 21: (.21) 19,000 miles - 3990 or AOOO miles.
Year 22: (.20) 19,000 miles - 3800 niles.
This same methodology was used to compute the mileage accumulation data
found in the emission factors document. Tables 3, 4, and 5 contain the
mileage accumulation data extended to the same number of years as the
scrappage data for LOT, HDG, and HDD.
The mileage accumulation .data shown in Tables 3, 4, and 5 repre-
sents the number of miles the average vehicle would travel in each year
of its life. This data is useful in that it accounts for the wide
variety of vehicle usage patterns.
Secondly, in computing the average annual mileage accumulation rate
for a fleet of vehicles the rate at which the vehicles in the fleet are
placed into service must also be considered. Assuming that vehicles are
sold at a constant rate throughout the model year, and each vehicle
accumulates its annual mileage (Tables 3, 4, 5) at a constant rate, the
desired values of average annual mileage accumulation for the fleet can
be computed.
If thex-assumptions stated in the previous paragraph are used then
the average vehicle in a fleet of new vehicles will be six months old at
the end of the first year and will have accumulated one half of the
annual mileage expected in Tables 3, 4, or 5. At the end of the second
year, the average vehicle in the fleet will be one and one-half years
old and will have accumulated all of the mileage expected by the average
vehicle during its first year plus one-half of the second year's mileage.
Using LLDT as an example:
Year 1: .5(15,900) = 7,950 miles
Year 2: .5(15,900) + .5(15,000) = 15,450 miles
Year 3: .5(15,000) + .5(14,000) = 14,500 miles
-------
Table 2
Fraction Reduction in Vehicle Miles Traveled with Age
Age
21
22
23
24
25
26
27
28
29
30
LPT
.24
.22
.20
.18
.16
.14
.12
.10
.08
.06
EDG
.21
.20
.19
.18
HDP
.17
.13
.10
.07
.05
.03
.01
-------
Table 3
<
Vehicle Mileage Accumulation Rates - LDT
Vehicle
Year
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
*A - annual
C - cumulative
LLDT
<6,000
A
15,900
15,000
14,000
13,100
12,200
11,300
10,300
9,400
8,500
7,600
6,700
6,600
6,200
5,900
5,500
5,100
5,000
4,700
4,400
4,000
3,700
3,400
3,100
2,800
2,400
2,100
1,800
1,500
1,200
900
Ibs GVW
C
15,900
30,900
44,900
58,000
70,200
81,500
91,800
101,200
109,700
117,300
124,000
130,600
136,800
142,700
148,200
153,300
158,300
163,000
167,400
171,400
175,100
178,500
181,600
184,400
186,800
188,900
190,700
192,200
193,400
194,300
HLDT
6-8,500 Ibs GVW
A C
15,700
15,700
14,100
12,600
11,300
10,200
9,400
8,600
8,000
7,500
7,100
6,600
6,300
6,000
5,500
5,200
5,000
4,700
4,400
4,100
3,800
3,500
3,100
2,800
2,500
2,200
1,900
1,600
1,300
900
15,700
31,400
45,500
58,100
69,400
79,600
89,000
97,600
105,600
113,100
120,200
126,800
133,100
139,100
144,600
149,800
154,800
159,500
163,900
168,000
171,800
175,300
178,400
181,200
183,700
185,900
187,800
189,400
190,700
191,600
-------
Table 4
Vehicle Mileage Accumulation Rate - HDG
Vehicle
Year Annual Cumulative
1 19,000 19,000
2 19,000 38,000
3 17,900 55,900
4 16,500 72,400
5 15,000 87,400
6 13,500 100,900
7 12,000 112,900
8 10,600 123,500
9 9,500 133,000
10 8,600 141,600
11 7,800 149,400
12 7,000 156,400
13 6,300 162,700
14 5,900 168,600
15 5,300 173,900
16 4,900 178,800
17 4,700 183,500
18 4,600 188,100
19 4,400 192,500
20 4,200 196,700
21 4,000 200,700
22 3,800 204,500
23 3,600 208,100
24 3,400 211,500
-------
Table 5
vehicle Milage Accumulation Rate -.HDD
Vehicle
Year Annual Cumulative
1 73,600 73,600
2 73,600 147,200
3 69,900 217,700
4 63,300 280,400
5 56,600 337,000
6 50,000 387,000
7 45,600 432,600
8 41,200 :473,800
9 38,200 512,000
10 36,000 548,000
11 34,600 582,600
12 33,800 616,400
13 33,100 649,500
14 32,400 681,900
15 30,900 712,800
16 28,700 741,500
17 25,700 767,200
18 21,300 788,500
19 18,400 806,900
20 15,400 822,300
21 12,600 834,900
22 9,600 844,500
23 7,400 851,900
24 5,000 856,900
25 3,700 860,600
26 2,200 862,800
27 700 863,500
-------
Thus, it can be seen that the average mileage accumulated by a vehicle
in a fleet in any year x will be one-half of the sum of the mileage
accumulation for year x and year (x-1). The final fleet average mileage
accumulation rates for LLDT, HLDT, HDG, and HDD are shown in Tables 6,
7, and 8 and Figures 2, 3, 4, and 5.
Thirdly, just as the vehicles were introduced at a constant rate in.
the model year, it can be assumed that the fraction of the total fleet
scrapped in any year is scrapped at a constant rate throughout that
year. Thus the total accumulated mileage on the average vehicle when it
is scrapped in year x is one half of the sum of the cumulative fleet
average annual mileage acccummulation in years x and (x-1). This mileage
at scrappage data will not be presented for the four vehicle groups
considered but will be shown in the sample lifetime calculation which
follows.
D. Calculations
As discussed previously, the average lifetime mileage periods can
be expressed mathematically as:
n
AIM = I f .m.
i^l1 1
Since the scrappage rates and average annual mileage accumulation rates
are now known, the average lifetime in miles, and indirectly in years,
can be obtained.
For example, consider heavy-duty gas trucks. As shown in Table 9,
using the scrappage and fleet average annual mileage accumulation rates,
the average lifetime mileage is computed at about 114,000 miles. To
determine the average number of years this represents, go back to Table
7 and find the approximate year by which the average lifetime mileage is
reached. In this case it is nine years.
Similar calculations can be made for LDTs and HDD with the following
results:
Type Vehicle Average Lifetime Periods—
LLDT £ 6,000 Ib GVWR 122,000 miles/ 12 years/j'
HLDT 6-8,500 Ib GVWR 119,000 miles/12 years/F/6/
LOT Composite 120,000 miles/12 years — —
HDG 114,000 railes/8 years
HDD 475,000 miles/9 years
same scrappage rates xrere used for LLDT and HLDT since these x^ere
computed for 0-10,000 Ib GVWR vehicles.
^/Assumes 55% of the LDTs are 6,000 Ibs CVWR or less and 45% are 6,001-
8,500 Ibs GVWR. These percentages are taken from the Mobile Source
Emission Factors document.
-------
6/TERA, Inc. under contract to Oak Ridge National Laboratory recently
estimated the average LDT lifetime at 122,300-132,000 miles and 11-12
years and the average passenger car lifetime at 87,300-97,300 miles and
9-10 years. See Vehicle - Miles of Travel Statistics, Lifetime Vehicle
Miles of Travel, and Current State Methods of Estimating Miles of
Travel, ORNL/TM-6327 Special, David L. Greene and Andrew S. Loebl,
February 1979.
7/A11 results rounded up to the nearest thousand miles.
-------
Table 6
Fleet Average Annual Mileage Accumulation Rates - LPT
Year
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
LLDT
Annual
7,950
15,450
14,500
13,550
12,650
11,700
10,800
9,850
8,950
8,050
7,150
6,650
6,400
6,050
5,700
5,300
5,050
4,850
4,550
4,200
3,850
3,550
3,250
2,950
2,600
2,250
1,950
1,650
1,350
1,050
Cumulative
7,950
23,400
37,900
51,450
64,100
75,800
86,600
96,450
105,400
113,450
120,600
127,250
133,650
139,700
145,400
150,700
155,750
160,600
165,150
169,350
173,200
176,750
180,000
182,950
185,550
187,800
189,750
191,400
192,750
193,800
. HLDT
Annual
7,850
15,700
14,900
13,350
11,950
10,750
9,800
9,000
8,300
7,750
7,300
6,850
6,450
6,150
5,750
5,350
5,100
4,850
4,550
4,250
3,950
3,650
3,300
2,950
2,750
2,350
2,050
1,750
1,450
1,100
Cumulative
7,850
23,550
38,450
51,800
63,750
74,500
84,300
93,300
101,600
109,350
116,650
123,500
129,950
136,100
•141,850
147,200
152,300
157,150
161,700
165,950
169,900
173,550
176,850
179,800
182,550
184,900
186,950
188,700
190,150
191,250
-------
3.00
LLDT RVE MILEflGE RCCUMULRTION
5.00
7.00
9.00
11.00
13.00
15.00 17.00
YEflRS
19.00
21.00
23.00
25^10
27.00
29.00
31.00
FIGURE" a
-------
HLDT RVE MILERGE RCCUMULRTION
1.00
5.00 7.00 -,. 9.00 11,00 13.00
15.00 17.00
YEflRS
19.00 • 21.00 ; 23.00 25.00 ' 27.00 29.00 31.C
-------
Table 7
Fleet Average Annual Mileage Accumulation Rates - HDG,
Year Annual Cumulative
1 9,500 9,500
2 19,000 28,500
3 18,450 46,950
4 17,200 64,150
5 15,750 79,900
6 14,250 94,150
7 12,750 106,900
8 11,300 118,200
9 10,050 128,250
10 8,950 137,200
11 8,200 145,400
12 7,400 152,800
13 6,650 159,450
14 6,100 165,550
15 5,600 171,150
16 5,100 176,250
17 4,800 181,050
18 4,650 185,700
19 4,500 190,200
20 4,300 194,500
21 4,100 198,600
22 3,900 202,500
23 3,700 206,200
24 3,500 209,700
-------
HDG flVE.MILERGE RCCUMULRTION
13.00
YEflRS
15.00
17.00
13.00
21,00
23.00
25.00
-------
Table 8
Fleet Average Annual Mileage Accmulation Rates - HDD
Year Annual Cumulative
1 36,800 36,800
2 73,600 110,400
3 71,750 182,150
4 66,600 248,750
5 59,950 308,700
6 53,300 362,000
7 47,800 409,800
8 43,400 453,200
9 39,700 492,900
10 37,100 530,000
11 35,300 565,300
12 34,200 599,500
13 33,450 632,950
14 32,750 665,700
15 31,150 696,850
16 29,800 726,650
17 27,200 753,850
18 23,500 777,350
19 19,850 797,200
20 16,900 814,100
21 14,000 828,100
22 11,100 839,200
23 8,500 847,700
24 6,200 853,900
25 4,350 858,250
26 2,950 861,200
27 1,450 862,650
-------
HDD flVE '• MI LEflGE flCCUMULflT I ON
ts.00
YERRS
-------
Table 9
Sample Average Lifetime Calculation - HDG
Year Scrappage Total Mileage Total Mileage
(i) Rate (fi) Accumulation When Scrapped (mi)
1 .00 9,500 4,750 0
2 .05 28,500 19,000 950
3 .07 46,950 37,725 2,641
4 .09 64,150 55,550 5,000
5 .10 79,900 72,025 7,203
6 .08 94,150 87,025 6,962
7 .07 106,900 100,525 7,037
8 .06 118,200 112,550 6,753
9 .05 128,250 123,225 6,161
10 .05 137,200 132,725 6,636
11 .05 145,400 141,300 7,065
12 .04 152,800 149,100 .5,964
13 .04 159,450 156,125 6,245
14 .05 165,550 162,500 8,125
15 .03 171,150 168,350 5,051
16 .03 176,250 173,700 5,211
17 .03 181,050 178,650 5,360
18 .03 185,700 183,375 5,501
19 .02 190,200 187,950 3,759
20 .02 194,500 192,350 3,847
21 .01 198,600 196,550 1,966
22 .01 202,500 200,550 2,006
23 .01 206,200 204,350 2,044
24 .01 209,700 207,950 2,080
1.00 113,567
I/See Table 7
^/Computed for year (i) by taking one-half of the sura of the average
mileage accumulation for year i and year (i-1).
-------
E. Discussion and Conclusions
As was stated previously, the lifetime periods calculated in this
report represent lifetime mileages and years for the average vehicle.
Light-duty trucks and heavy-duty vehicles operate in a wide variety of
applications, 'usage patterns, load variations, environmental conditions,
maintenance schedules and other operator-induced variables which may
significantly affect the representativeness of these figures. The
analysis in this report gives one method by which the average lifetiae
period can be computed which inherently accounts for the effects of the
variables discussed above. It should be possible for each manufacturer
to deduce a more definitive lifetime period for its vehicles and/or
engines based on the characteristics of each vehicle/engine line and the
vehicle/engine application. The average lifetime mileage figures
calculated above are useful because they represent the average for a
wide variety of operating conditions and are characteristic of the
vehicle classes as a whole.
The average lifetime periods in this report are based on vehicle
scrappage rates and not engine retirement or rebuild rates. This leads
to the question of the relationship, if any, between average lifetime
periods and average periods to engine retirement or rebuild. The
definition of engine retirement is obvious,1i.e. engine scrappage, but
the definition of engine rebuild is not as clear. A report prepared by
Arthur D. Little, Inc.jB/ indicates that vehicle/engine manufacturers
consider the average lifetime to be the length of time or distance the
engine may be operated before an "in-frame" overhaul is required. Such
overhauls include inspection and replacement as required of those parts
which can be removed from the- engine without removing the engine from
the frame, of the vehicle. Parts included in this type of overhaul
include valves, pistons, piston rings, cylinder liners, and connecting
rod bearings.
To provide some means of comparison between average lifetime
periods and average periods to overhaul some average period to overhaul
data is shown in Table 10.
In comparing these periods no firm conclusions can be draxm.
However, some preliminary conclusions are possible:
(1) The average heavy-duty diesel engine undergoes at least one
and possibly tv/o overhauls prior to vehicle scraopage'.
(2) Heavy-duty gasoline-fueled engines are just as likely scrapped
as rebuilt.
ji/"Heavy-Duty Vehicle Engine Service Accumulation Cycle," Arthur D.
Little, Inc., April 1977, EPA Contract 68-03-2372, this is an unapproved
draft report available in public docket vOMSAPC 78-4.
-------
Table 10
Life to Overhaul Data
Engine Type
HDD <>30K GVWR)
250 HP Turbocharged
; Diesel - HDD
HDD
HDD
Medium-Duty
Diesel
Diesel Bus
Light-Duty Gas
HDG
Service Type
linehaul
linehaul
linehaul
urban
urban
urban
variable
variable
Life to Overhaul (miles)
300,000 - 500,000
280,000
500,000
300,000
150,000
125,000 -
200,000
200,000 -
250,000
100,000
100,000
Type of Overhaul
out-of-frame
in-frame
out-of-frame
in-frame
in-frame
out-of-frame
in-frame
out-of-frame
in-frame
I/
!/
I/
I/
I/
11
I-1
I/
- Society of Automotive Engineers, SAE Paper 750128.
II
-Society of Automotive Engineers, SAE Paper 700665.
3/
- Heavy-Duty Vehicle Engine Service Accumulation Cycle," Arthur D. Little, Inc.,
April 1977, EPA Contract 68-03-2372, an unapproved draft report available in
public docket //OMSAPC 78-4.
-------
-24-
(3) Urban usage leads to much shorter lifetime mileage than
over the road usage.
(4) LDTs are more likely retired and .replaced in lieu of re-
building the engine.
The average lifetime periods presented above for light-duty
trucks and heavy-duty vehicles have been computed using sound technical
methods and engineering judgement. These lifetime mileages and periods
are the values which will be used in future rulemaking actions to compute
emissions reductions, costs, and cost effectiveness.
------- |