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OCR for page 63
4
Impact of a More Fuel-Efficient Fleet
If the technologies described in Chapter 3 are imple-
mented, making vehicles more fuel efficient, there will be a
variety of impacts. This chapter explores the potential im-
pacts on energy demand and greenhouse gas emissions, cost-
efficient levels of fuel economy, industry and employment,
and safety.
ENERGY DEMAND AND GREENHOUSE GAS IMPACT
The fuel economy of light-duty cars and trucks and ve-
hicle miles traveled (VMT) are the two most important fac-
tors underlying the use of energy and release of greenhouse
gases in the light-duty fleet. Energy consumption during the
manufacture of various components of the vehicles and their
fuels is a lesser, but still significant, consideration in the life-
cycle analyses of energy use and greenhouse gas emissions.
Numerous projections were examined by the committee on
possible future energy use and greenhouse gas emissions-
for example, DeCicco and Gordon (1993), Austin et al.
(1999), Charles River Associates (1995), EIA (2001),
Patterson (1999), Greene and DeCicco (2000~. To choose
the best technology for overall energy efficiency, one must
consider a "well-to-wheels" (WTW) analysis such as those
that are described in Attachment 4A. The following discus-
sion is designed to illustrate the impact of possible fuel
economy changes and should not be interpreted in any way
as a recommendation of the committee.
The committee calculated the potential magnitude of fuel
savings and greenhouse gas emission reductions if new passen-
ger car and light-truck fuel economy (in mpg) is increased by
15 percent, 25 percent, 35 percent, and 45 percent. These in-
creases are assumed to be phased in gradually beginning in 2004
and to reach their full value in 2013. New vehicle sales shares
of passenger cars and light trucks were held constant. Green-
house gas emissions are for the complete WTW cycle based on
the GREET model and include carbon dioxide, methane, and
nitrogen oxides (Wang, 1996; Wang and Huang, 1999~. The
fuel for all light-duty vehicles is assumed to be gasoline, 70
percent conventional and 30 percent reformulated.
63
Allowance is made for a rebound effect that is, a small
increase in miles driven as fuel economy increases. Because
of the long time required to turn over the fleet, the calcula-
tions were extended to the year 2030 to show the longer-
range impacts of the increases in fuel economy. However,
new vehicle mpg was held constant after 2013.
The base case approximates the 2001 Annual Energy
Outlook forecast of the Energy Information Administration
(EIA) except that the vehicle miles traveled are assumed to
increase to 1.7 percent per year, slightly less than the 1.9
percent assumed by EIA. However, unlike the EIA forecast,
fuel economy is assumed to remain constant. In the base
case, annual gasoline use is projected to increase from 123
billion gallons (8 mmbd) in 2001 to 195 billion gallons (12.7
mmbd) by 2030 (Figure 4-1~.
The magnitude of gasoline savings that could be achieved
relative to the base case for various fuel economy increases
between now and 2030 is shown in Figure 4-2. As a result of
~ Base Case
250000-
200000-
a, 150000-
Q
U)
O
1 00000-
o
50000-
O -
:: 15% MPG Increase
~ 25% MPG Increase
+ 35% MPG Increase
~ ~ 45% MPG Increase
O~Co~
l
l
2000 2005 2010 2015 2020 2025 2030
FIGURE 4-1 Fuel use in alternative 2013 fuel economy scenarios.
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64
EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS
these hypothetical fuel economy increases, fuel savings in
2015 range from 10 billion gallons for a 15 percent fuel
economy increase to 25 billion gallons for a 45 percent in-
crease. By 2030 the fuel savings would be 22 billion gallons
and 55 billion gallons for fuel economy increases of 15 per-
cent and 45 percent, respectively. Since greenhouse gas
emissions are correlated closely with gasoline consumption
(Figure 4-1), they show a similar pattern (Figure 4-3~.
Growth in greenhouse gas emissions still occurs through
2030, but the growth is slower than it would have been with-
out improved fuel economy (Figure 4-4~.
ANALYSIS OF COST-EFFICIENT FUEL ECONOMY
The committee takes no position on what the appropriate
level of fuel economy should be. The question, however, is
often raised of how much investment in new technology to
increase fuel economy would be economically efficient. That
is, when does the incremental cost of new technology begin
to exceed the marginal savings in fuel costs? Consumers
might not choose to use this technology for fuel economy;
they might choose instead to enhance other aspects of the
vehicles. Such an estimate, however, provides an objective
measure of how much fuel economy could be increased
while still decreasing consumers' transportation costs. The
committee calls this the cost-efficient level of fuel economy
improvement, because it minimizes the sum of vehicle and
fuel costs while holding other vehicle attributes constant.
The committee identified what it calls cost-efficient tech-
nology packages: combinations of existing and emerging
technologies that would result in fuel economy improve-
ments sufficient to cover the purchase price increases they
would require, holding constant the size, weight, and perfor-
mance characteristics of the vehicles.
-- ----------- 45% MPG Increase
35% MPG Increase | A 250
70000 -
Pnnnn -
_
50000-
40000-
~n
~~ 30000-
c~
° 20000-
~n
o
1 0000 -
| · 25% MPG Increase
15% MPG Increase ~ 200
.. .
, ...
.. ,, : ~
.....
.... NS
''x
O ~ ~~
2000 2005 2010 2015 2020 2025 2030
FIGURE 4-2 Fuel savings of alternative 2013 fuel economy im-
provement targets.
70o.ol
600.0-
500.0-
Q
O 400.0- 3---
" 300.0-
5
TO 200.0-
~n
to 1 Go n-
5
Base Case
1 5% M PG I ncrease
25% M PG I ncrease
35% MPG Increase
45% M PG I ncrease
’~
A.= I-- .; 2.~ ~2 ~2~ ~
' 0.0- lllllllllllllllllllllllllllllll
2000 2005 2010 2015 2020 2025 2030
FIGURE 4-3 Fuel-cycle greenhouse gas emissions in alternative
2013 fuel economy cases.
The essence of analyzing cost-efficient fuel economy is
determining at what fuel economy level the marginal costs
of additional fuel-saving technologies equal the marginal
benefits to the consumer in fuel savings. However, such
analysis is conditional on a number of critical assumptions,
about which there may be legitimate differences of opinion,
including (1) the costs and fuel-efficiency effect of new tech-
nology and (2) various economic factors. The committee
states its assumptions carefully and has investigated the ef-
fect of varying several key parameters.
Perhaps the most critical premise of this cost-efficient
analysis is that key vehicle characteristics that affect fuel
i 45% MPG Increase
~ 35% MPG Increase
+ 25% MPG Increase
15% MPG Increase
150-
u'
~ 100-
._
50-
a
O
.......... :
....... ..
.. .. .......
..
'""I
. 35' ins ~ ~~~
2000 2005 2010 2015 2020 2025 2030
FIGURE 4-4 Greenhouse gas emissions reductions from hypo-
thetical alternative fuel economy improvement targets.
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IMPACT OF A MORE FUEL-EFFICIENT FLEET
economy are held constant: (1) acceleration performance,
(2) size, in terms of functional capacity, (3) accessories and
amenities, and (4) the mix of vehicle types, makes, and mod-
els sold. These factors are held constant for analytical clarity
and convenience. Once one begins altering vehicle charac-
teristics, the trade-off between fuel economy and cost be-
comes obscured in the myriad of other simultaneous changes
of design and function that could be made. Since there is no
obviously correct way to forecast future vehicle attributes
and the sales mix, the committee holds them constant. In
real-world markets, all of these factors will change over time
and could have important implications for achieving a spe-
cific fuel economy goal.
Other key assumptions pertain to how consumers value
fuel economy. The price for higher fuel economy technol-
ogy is paid when a vehicle is purchased. Fuel savings accrue
in the future, depending on how much a vehicle is driven and
under what circumstances. Important uncertainties involve
consumers' expectations about future fuel prices, the rates
of return they will expect on investments in higher fuel
economy, and their perception of how used-vehicle markets
will value fuel economy. Not only are the average values of
these key parameters uncertain, but they will certainly vary
from consumer to consumer and from one market segment
to another.
Incorporating all these uncertainties into the cost-efficient
analysis would require a far more complex model and far
more time to implement than the committee has available.
Instead, the committee uses sensitivity analysis to illustrate
the potential impacts of key assumptions on the outcomes of
the cost-efficient analysis.
Despite the many uncertainties, the cost-efficient analy-
sis is valuable for illustrating the range of feasible fuel
economy improvement and the general nature of the cost of
achieving higher fuel economy. However, it is critically im-
portant to keep in mind that the analysis is conditional on the
assumptions of constant vehicle attributes and a number of
key parameter values. Changing these assumptions would
change the results, as the sensitivity analysis shows.
The cost-efficient analysis uses estimates of the costs of
technologies and their impacts on fuel consumption in Chap-
ter 3 (see Tables 3-1 through 3-3~. Only technologies known
to be capable of meeting future emissions standards and hav-
ing either positive or small negative effects on other vehicle
attributes were used. The technologies were reordered by
cost-effectiveness, so that the order of implementation re-
flects increasing marginal cost per unit of fuel saved. Cost
effectiveness is measured by the ratio of the midpoint fuel
consumption reduction to the midpoint cost estimate. While
this may not correspond to the actual order in which tech-
nologies are implemented by auto manufacturers, it is none-
theless the most appropriate assumption for analyzing the
economic trade-off between vehicle price and fuel savings.
The Path 3 technology scenario was used because all of the
Path 3 technologies could be in full-scale production by 2013
65
to 2015. The data in Tables 3-1 through 3-3 were used to
construct fuel economy supply functions and confidence
bounds on those functions. The supply functions are com-
bined with functions describing consumers' willingness to
pay for higher fuel economy and are solved for the point at
which the cost of increasing fuel economy by 1 mile per
gallon equals its value to the consumer.
Three curves were constructed for each vehicle class to
reflect the range of uncertainty shown in the tables in Chap-
ter 3. The high cost/low fuel economy and low cost/high fuel
economy curves provide a reasonable set of bounds for the
average cost/average fuel economy curve. For the method
used, see Greene (2001~.
Consumers' willingness to pay is estimated using aver-
age data on vehicle usage, expected payback times, gasoline
at $1.50 per gallon, and assumed rates of return on the
consumer's investment in higher fuel economy. The key ar-
eas of uncertainty are the rate of return consumers will de-
mand and the length of time over which they will value
future fuel savings. Because each additional mile per gal-
lon saves less fuel than the one before, the marginal willing-
ness to pay for fuel economy will decline as fuel economy
Increases.
The cost-efficient point (at which the marginal value of
fuel saved equals the marginal cost) is then found, assuming
a fuel priced at $1.50 per gallon. This produces three fuel
economy estimates for each vehicle class, reflecting the three
curves. Finally, two cases are considered in which the key
parameters of consumer discount rate and payback time are
varied.
The following calculations for cost-efficient fuel effi-
ciency are based on the key assumptions summarized in
Table 4-1 for passenger cars and light-duty trucks. Two cases
TABLE 4-1 Key Assumptions of Cost-Efficient Analysis
for New Car and Light Truck Fuel Economy Estimates
Using Path 3 Technologies and Costs (see Chapter 3)
Assumption
Case 1
Case 2
First-year travel for new vehicles (mi/yr)
Rate of decrease in vehicle use (%/yr)
Payback time (yr)
Rate of return on investment (%)
Base fuel economy (mpg)
Subcompact cars
Compact cars
Midsize cars
Large cars
Small SUVs
Midsize SUVs
Large SUVs
Minivans
Small pickups
Large pickups
On-road fuel economy (moo) shortfall (%)
15,600
4.5
14
12
31.3
30.1
27.1
24.8
24.1
21.0
17.2
23.0
23.2
18.5
15
Effect of safety and emissions standards (%) -3.5
15,600
4.5
3
o
31.3
30.1
27.1
24.8
24.1
21.0
17.2
23.0
23.2
18.5
15
-3.5
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66
EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS
are developed. In Case 1 it is assumed that vehicles are driven
15,600 miles in the first year, decreasing thereafter at 4.5
percent/year, and that a gallon of gasoline costs $1.50 (1999
dollars). Payback time is the vehicle lifetime of 14 years.
Base fuel economy is shown for each class of vehicles. It is
assumed that there will be a 15 percent reduction in on-the-
road gasoline mileage from the EPA combined test data. It is
also assumed that there will be a 3.5 percent fuel economy
penalty as a result of weight gains associated with future
safety and emissions requirements and that consumers re-
quire a rate of return of 12 percent on the money spent on
fuel economy. Because this last assumption is more subjec-
tive than the others, Case 2 was developed using a payback
of 3 years at zero percent discount rate. This case represents
the perspective of car buyers who do not value fuel savings
over a long time horizon. Case 1 might be the perspective of
policy makers who believe that the national interest is served
by reducing fuel consumption no matter how many people
own a vehicle over its lifetime.
The results of the cost-efficient analysis for Case 1 are
shown in Table 4-2. Using the assumptions shown in Table
4-1, the calculation indicates that the cost-efficient increase
in (average) fuel economy for automobiles could be in-
creased by 12 percent for subcompacts and up to 27 percent
for large passenger cars. For light-duty trucks, an increase of
25 to 42 percent (average) is calculated, with the larger in-
creases for larger vehicles.
For example, Table 4-2 shows that a new midsize SUV
typically (sales-weighted average) has a base fuel economy
today of 21.0 mpg. The adjusted base (20.3 mpg) reflects the
3.5 percent fuel economy penalty for weight increases to
meet future safety and emission standards. In the column
labeled "Average," the cost-efficient fuel economy is
28.0 mpg. The percent improvement over the unadjusted
base of 21.0 is 34 percent (shown in parentheses). The cost
to obtain this improved fuel economy is estimated at $1,254.
However, there is wide uncertainty in the results. This is
illustrated in the other two columns, which show an optimistic
case (low cost/high fuel economy curve) and a pessimistic
case (high cost/low fuel economy curve). In the low cost/high
fuel economy column, the cost-efficient fuel economy
increases to 30.2 mpg, for an improvement of 44 percent at a
cost of $1,248. In the high cost/low mpg column, the fuel
economy is 25.8 mpg, for an improvement of 23 percent at a
cost of $1,589. In some cases the high cost/low mpg column
will have a lower cost (and a significantly lower mpg) than the
low cost/high mpg column because of the nature of the cost-
efficient calculation and the relative slopes of the cost curves.
There is some evidence suggesting that consumers do not
take a 14-year view of fuel economy when buying a new car.
For that reason, Table 4-3 shows the cost-efficient fuel
economy levels for 3-year payback periods. For cars, aver-
age cost-efficient levels are between 0.1 and 1.5 mpg higher
than their respective adjusted base fuel economy levels, with
the larger increases for the larger cars. The cost-efficient
levels of the light-duty trucks are about 1.4 to 3.1 mpg higher
than their respective adjusted base fuel economy levels, with
the larger increases being associated with the larger trucks.
The negative changes in fuel economy shown in Table 4-3
are because the base is used for this calculation. All vehicles
still improve relative to the adjusted base, even in the high
cost/low mpg column.
As shown in Table 4-2, for the 14-year payback (12 per-
cent discount) case, the average cost-efficient fuel economy
levels are between 3.8 and 6.6 mpg higher than their respec-
tive (unadjusted) bases for passenger cars, with the larger
increases associated with larger cars. For light-duty trucks,
the cost-efficient levels are about 6 to 7 mpg higher than the
base fuel economy levels, with the larger increases associ-
ated with larger trucks.
The cost-efficient fuel economy levels identified in Tables
4-2 and 4-3 are not recommended fuel economy goals. Rather,
they are reflections of technological possibilities and eco-
nomic realities. Other analysts could make other assumptions
about parameter values and consumer behavior. Given the
choice, consumers might well spend the money required to
purchase the cost-efficient technology packages on other
vehicle amenities, such as greater acceleration, accessories, or
towing capacity.
The fuel economy and cost data used in this study are
compared with the data used in other recent studies in Fig-
ures 4-5 and 4-6 for cars and light trucks, respectively. The
cost curves used in this study are labeled NRC 2001 Mid
(average), NRC 2001 Upper (high cost/low mpg upper
bound), and NRC 2001 Lower (low cost/high mpg lower
bound). For comparison with two other studies, one by Si-
erra Research (Austin et al., 1999) and one by Energy and
Environmental Analysis (EEA, 2001), the NRC curves were
normalized to the sales-weighted average fuel economies of
the new passenger car and light truck fleets. For passenger
cars, the NRC average curve (NRC 2001 Mid) is similar to
the Sierra curve (up to about 11 mpg increase) and slightly
more optimistic than the EEA curve.
The Massachusetts Institute of Technology (MIT) (Weiss
et al., 2000) and American Council for an Energy-Efficient
Economy (ACEEE) (DeCicco et al., 2001) curves were ob-
tained differently as they are based on complete, specific
vehicles embodying new technology. The NRC, Sierra, and
EEA analyses added technology incrementally. Neither the
MIT nor the ACEEE studies present their results in the form
of cost curves; the curves shown here are the committee's
inferences based on data presented in those reports.
The MIT curve is calculated using the lowest cost and
most fuel-efficient vehicles in the study, which uses advanced
technology and a midsize sedan and projects to 2020. Simi-
larly, the ACEEE-Advanced curves in Figures 4-5 and 4-6
are based on individual vehicles and advanced technology
options. Both studies are substantially more optimistic than
this committee's study, having used technology/cost options
more advanced than those considered by the committee.
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IMPACT OF A MORE FUEL-EFFICIENT FLEET
TABLE 4-2 Case 1: Cost-Efficient Fuel Economy (FE) Analysis for 14-Year Payback (12% Discount Rateja
Low Cost/High mpg Average High Cost/Low mpg
Base Base FE Cost Savings FE Cost Savings FE Cost Savings
Vehicle Class mpgb AdjustedC mpg, (%) ($) ($) mpg, (%) ($) ($) mpg, (%) ($) ($)
Subcompact 31.3 30.2 38.0(21) 588 1,018 35.1 (12) 502 694 31.7 (1) 215 234
Compact 30.1 29.1 37.1 (23) 640 1,121 34.3 (14) 561 788 31.0 (3) 290 322
Midsize 27.1 26.2 35.4 (31) 854 1,499 32.6 (20) 791 1,140 29.5 (9) 554 651
Large 24.8 23.9 34.0 (37) 1,023 1,859 31.4 (27) 985 1,494 28.6 (15) 813 1,023
Light trucks
Small SUVs 24.1 23.3 32.5 (35) 993 1,833 30.0 (25) 959 1,460 27.4 (14) 781 974
Mid SUVs 21.0 20.3 30.2 (44) 1,248 2,441 28.0 (34) 1,254 2,057 25.8 (23) 1,163 1,589
Large SUVs 17.2 16.6 25.7 (49) 1,578 3,198 24.5 (42) 1,629 2,910 23.2 (35) 1,643 2,589
Minivans 23.0 22.2 32.0 (39) 1,108 2,069 29.7 (29) 1,079 1,703 27.3 (19) 949 1,259
Small pickups 23.2 22.4 32.3 (39) 1,091 2,063 29.9 (29) 1,067 1,688 27.4 (18) 933 1,224
Large pickups 18.5 17.9 27.4 (48) 1,427 2,928 25.5 (38) 1,450 2,531 23.7 (28) 1,409 2,078
aOther key assumptions: See Table 4-1.
bBase is before downward adjustment of -3.5 percent for future safety and emissions standards.
CBase after adjustment for future safety and emissions standards (-3.5 percent).
TABLE 4-3 Case 2: Cost-Efficient Fuel Economy (FE) Analysis for 3-Year Payback (Undiscountedja
Low Cost/High mpg Average High Cost/Low mpg
Base Base FE Cost Savings FE Cost Savings FE Cost Savings
Vehicle Class mpgb AdjustedC mpg, (%) ($) ($) mpg, (%) ($) ($) mpg, (%) ($) ($)
Subcompact 31.3 30.2 33.3 (6) 180 237 30~3 (-3) 11 11 30.2 (-4) 0 0
Compact 30.1 29.1 32.3 (7) 202 268 29.1 (-2) 29 29 29.1 (-4) 0 0
Midsize 27.1 26.2 29.8 (10) 278 363 26.8 (-1) 72 76 26.2 (-4) 0 0
Large 24.8 23.9 28.2 (14) 363 488 25.4 (3) 173 190 23.9 (-4) 0 0
Light trucks
Small SUVs 24.1 23.3 27.3 (13) 358 492 24.7 (2) 174 193 23.3 (-4) 0 0
Mid SUVs 21.0 20.3 25.0 (19) 497 721 22.7 (8) 341 407 20.3 (-4) 0 0
Large SUVs 17.2 16.6 21.1 (23) 660 992 19.7 (15) 567 740 18.3 (6) 373 424
Minivans 23.0 22.2 26.5 (15) 411 570 24.2 (5) 247 284 22.2 (-4) 0 0
Small pickups 23.2 22.4 26.9 (16) 412 579 24.4 (5) 247 285 22.4 (-4) 0 0
Large pickups 18.5 17.9 22.7 (23) 600 918 20.8 (12) 477 608 18.7 (1) 178 189
aOther key assumptions: See Table 4-1.
bBase is before downward adjustment of -3.5 percent for future safety and emissions standards.
CBase after adjustment for future safety and emissions standards (-3.5 percent).
In Figure 4-6, the committee' s curve (NRC) is more opti-
mistic than the Sierra curve and similar to the EEA curve.
The ACEEE-Advanced curve, which is based on vehicles as
discussed for cars above, is much more optimistic. It uses
technology/cost options beyond those used for the com-
mittee's cost-efficient optimization.
67
POTENTIAL IMPACTS ON THE DOMESTIC
AUTOMOBILE INDUSTRY
Regulations to increase the fuel economy of vehicles will
require investments by automakers in R&D and tooling and
will thus increase the costs of new vehicles. They will also
OCR for page 68
68
$5,000
<~ $4,000 -
c'
<~, $3,000 -
.O
._ $2,OOO -
$1 ,000
$0 ~
0 5 10 15 20 25
EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS
2014 Sierra Res.
~ 2020 M IT
+ ACEEE-Advanced
+ 2013-15 EEA
N RC 2001 Mid
N RC 2001 Upper
NRC 2001 Lower
~ EEA w/o wgt
Increase in MPG
FIGURE 4-5 Passenger car fuel economy cost curves from selected
studies.
+ 2014 Sierra Res.
~ ACEEE-Advanced
+2013-15 EEA
N RC 2001 Mid
~NRC2001 Upper
NRC 2001 Lower
~ EEA w/o WGT
$5,000
$4,000
c'
c'
._
._ $2,000
$3,000
$1 ,OOo
$0
0 5 10
Increase in MPG
-
15 20 25
FIGURE 4-6 Light-truck fuel economy cost curves from selected
studies.
divert resources that would otherwise go toward satisfying
consumers' demands for performance, styling, and other
vehicle features. No regulation is without cost to consumers
or manufacturers. The impacts of CAFE standards in the past
are reviewed in Chapter 2.
Looking Forwarcl at the Automobile Market
As noted in Chapter 2, GM, Ford, and the Chrysler divi-
sion of DaimlerChrysler will post lower profits in 2001 ow-
ing to the slower economy and the sharp rise in buyer incen-
tives that the companies need to offer to maintain their
market shares. Vehicle demand is expected to decline in 2001
from 17.4 million in 2000, with the final number depending
in large part on the level of rebates and other incentives.
Foreign companies' share of the U.S. market has grown
steadily and is now about 36 percent, compared with 26 per-
cent in 1993. In 2000, GM, Ford, and Chrysler combined
lost 3 percentage points in market share, and so far in 2001
have lost another 1.4 percentage points (despite per-unit in-
centives that are the highest in history and often triple the
marketing support on competing foreign models). The gain
in market share of foreign companies has accelerated in re-
cent years as foreign manufacturers entered the light truck
market with models that competed with traditional Ameri-
can pickups, minivans, and SUVs. They also created a new
category, the crossover vehicle, which is built on a car chas-
sis but looks like an SUV and may be classed as a light truck
for fuel economy regulation. (Examples include the Toyota
RAY-4 and Honda CRY.)
The erosion in profit margins and income at GM, Ford,
and Chrysler began in 2000 as pricing pressures, once con-
fined to passenger cars, spread into the light-truck sector and
sales slowed. The supply of light trucks, until recently bal-
anced against sharply rising demand, had allowed vehicle
manufacturers to aggressively price these products. Although
the Big Three still dominate the light-truck market with a 77
percent share, that is down from 86 percent in 1993 as a
result of new products and capacity from Asian and Euro-
pean manufacturers. Additional North American truck ca-
pacity from Honda in Alabama and Toyota in Indiana and
expansion of capacity by BMW and Nissan will add at least
750,000 units of new truck supply to the market over the
next 3 years. Given the recent success of foreign manufac-
turers with new models and advanced technology (see Chap-
ter 3), their share of the truck segment is likely to rise further
in the coming years.
To cope with falling profits and lower cash balances, auto
companies have cut back on discretionary spending, eliminated
jobs through voluntary retirement plans, and now appear to be
delaying product launch schedules. Standard & Poor's, the ar-
biter of creditworthiness, recently lowered its outlook on GM
and Ford from stable to negative (Butters, 2001~.
Even if vehicle demand rebounds in 2002 to the 17 mil-
lion-unit level, industry profits are not expected to recover
OCR for page 69
IMPACT OF A MORE FUEL-EFFICIENT FLEET
soon to historic levels. Increased competition could reduce
truck profits to half of their former levels. If the proliferation
of foreign brand crossover models draws buyers away from
larger, heavier, and more expensive domestic models, the
financial impact on the industry will be greater.
This is a difficult environment for GM, Ford, and the
Chrysler division of DaimlerChrysler. In less than 3 years,
Chrysler went from being the most profitable vehicle manu-
facturer in the country to a merger with Daimler that was
forced by financial distress. While GM and Ford are in rea-
sonable financial health, they cannot count on truck profits
to generate above-average returns as they did in the past.
Nevertheless, the industry could adjust to possible
changes in CAFE standards if they were undertaken over a
long period of time, consistent with normal product life
cycles. An abrupt increase in fuel economy standards (espe-
cially one that hurt the industry's ability to sell light trucks)
would be more costly. A single standard that did not differ-
entiate between cars and trucks would be particularly diffi-
cult to accommodate.
Criteria for Judging Regulatory Changes
The impacts on industry of changing fuel economy stan-
dards would depend on how they were applied. Some of the
more important criteria are discussed here.
Timing and Scale of Increase
Raising standards too steeply over too short a time would
require manufacturers to absorb much of the cost of obtain-
ing or developing technology and tooling up to produce more
efficient vehicles. It would lead to sharp increases in costs to
manufacturers (and thus consumers). The benefits of pre-
cipitous increases in CAFE standards would flow instead to
machine tool companies, component manufacturers, and de-
velopers of vehicle technology. Automakers would be forced
to divert funds and talent away from longer-term investments
(such as the PNGV). Given sufficient planning time, how-
ever, industry can adapt. Chapter 3 discusses the costs and
timing involved in introducing fuel-saving technology. Gen-
erally, little change can be expected over the next few years,
and major changes would require a decade.
Equivalence of Impact
If new regulations favor one class of manufacturer over
another, they will distribute the costs unevenly and could
evoke unintended responses. In general, new regulations
should distribute the burden equally among manufacturers
unless there is a good reason not to. For example, raising the
standard for light trucks to that of cars would be more costly
for light-truck manufacturers. On the other hand, tightening
the standards for passenger vehicles while leaving light
trucks alone would favor another set of manufacturers. A
69
current proposal to simply increase the standard for light-
duty trucks to the current level of the standard for passenger
cars would operate in this inequitable manner. The rise of
the crossover SUV will add to the challenge of finding a
balanced approach.
Flexibility
In general, regulations that allow manufacturers flexibil-
ity in choosing how to achieve the desired policy goal (such
as reducing fuel use or improving safety) are likely to lower
the costs to the nation. That is because restricting the avail-
able technology options will reduce chances for cost-saving
innovations. To the extent possible, consistent with the over-
all policy goals, flexibility is an important criterion. This is
one reason for the committee's enthusiasm for traceable fuel
economy credits, as described in this chapter.
Hiciclen Costs of Forcing Technical Innovation
In general, it is risky to commercialize technologies while
they are still advancing rapidly. Pioneering purchasers of
vehicles that incorporate highly efficient new technology
could find that these vehicles depreciate faster than those
with old technology if the new technology results in higher
repair costs or is replaced by improved versions. For the
same reason, leavers might be reluctant to write leases on
vehicles that are radically different and therefore have un-
predictable future demand. GM offered its own leases on the
EV1 (an electric vehicle) but did not sell the vehicle because
it recognized that the car might be unusable in a few years
because of technological obsolescence or high maintenance
costs.
On the other hand, as explained in Chapter 3, foreign
manufacturers are rapidly improving their technology,
largely because their main markets are in countries with high
fuel prices or high fuel economy standards. Not only are
their vehicles economical (and frequently low in emissions),
but they are proving popular because they offer other at-
tributes valued by consumers, such as power and improved
driving characteristics. Insofar as higher fuel economy stan-
dards force domestic manufacturers to adopt new technol-
ogy, it could improve their competitiveness.
SAFETY IMPLICATIONS OF FUTURE INCREASES IN
FUEL ECONOMY
In Chapter 2 the committee noted that the fuel economy
improvement that occurred during the 1970s and early 1980s
involved considerable downweighting and downsizing of the
vehicle fleet. Although many general indicators of motor
vehicle travel safety improved during that period (e.g., the
fatality rate per vehicle mile traveled), the preponderance of
evidence indicates that this downsizing of the vehicle fleet
resulted in a hidden safety cost, namely, travel safety would
OCR for page 70
70
EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS
have improved even more had vehicles not been downsized.
Based on the most comprehensive and thorough analyses
currently available, it was estimated in Chapter 2 that there
would have been between 1,300 and 2,600 fewer crash
deaths in 1993 had the average weight and size of the light-
duty motor vehicle fleet in that year been like that of the
mid-1970s. Similarly, it was estimated there would have
been 13,000 to 26,000 fewer moderate to critical injuries.
These are deaths and injuries that would have been prevented
in larger, heavier vehicles, given the improvements in ve-
hicle occupant protection and the travel environment that
occurred during the intervening years. In other words, these
deaths and injuries were one of the painful trade-offs that
resulted from downweighting and downsizing and the re-
sultant improved fuel economy.
This section of Chapter 4 addresses the question of how
safety might be affected by future improvements in fuel
economy. The key issue is the extent to which such improve-
ments would involve the kind of vehicle downweighting and
downsizing that occurred in the 1970s and 1980s. In Chap-
ter 3 the committee examined the methods by which the in-
dustry can improve fuel economy in the future and identified
many potential improvements in powertrains, aerodynam-
ics, and vehicle accessories that could be used to increase
fuel economy. Earlier in Chapter 4 the committee concluded
that many of these technologies could pay for themselves in
reduced fuel costs during the lifetimes of vehicles. Thus, it is
technically feasible and potentially economical to improve
fuel economy without reducing vehicle weight or size and,
therefore, without significantly affecting the safety of motor
vehicle travel. Two members of the committee believe that
it may be possible to improve fuel economy without any
implication for safety, even if downweighting is used. Their
dissent forms Appendix A of this report.
The actual strategies chosen by manufacturers to improve
fuel economy will depend on a variety of factors. Even if the
technology included in the cost-efficient fuel economy im-
provement analyses is adopted, that technology might be
used to provide customers with other vehicle attributes (per-
formance, size, towing capacity) that they may value as much
as or more than fuel economy. While it is clear vehicle
weight reduction is not necessary for increasing fuel
economy, it would be shortsighted to ignore the possibility
that it might be part of the response to increases in CAFE
standards.
In fact, in meetings with members of this committee, au-
tomotive manufacturers stated that significant increases in
fuel economy requirements under the current CAFE system
would be met, at least in part, by vehicle weight reduction.
Because many automakers have already emphasized weight
reduction with their current vehicle models, they also stated
that substantial reductions in weight probably could not oc-
cur without some reduction in vehicle size. They were refer-
ring to exterior dimensions, not to interior space, which is a
high customer priority. However, this type of size reduction
also reduces those portions of the vehicle that provide the
protective crush zones required to effectively manage crash
energy.
When asked about the potential use of lighter materials to
allow weight reduction without safety-related size reduc-
tions, the manufacturers acknowledged that they were gain-
ing more experience with new materials but expressed con-
cern about their higher costs. Given that concern, industry
representatives did not expect that they could avoid reducing
vehicle size if substantial reductions in vehicle weight were
made. Thus, based on what the committee was told in direct
response to its questions, significant increases in fuel
economy requirements under the current CAFE system could
be accompanied by reductions in vehicle weight, and at some
level, in vehicle size.
The committee recognizes that automakers' responses
could be biased in this regard, but the extensive down-
weighting and downsizing that occurred after fuel economy
requirements were established in the 1970s (see Chapter 2)
suggest that the likelihood of a similar response to further
increases in fuel economy requirements must be considered
seriously. Any reduction in vehicle size and weight would
have safety implications. As explained in Chapter 2, there is
uncertainty in quantifying these implications. In addition,
the societal effects of downsizing and downweighting de-
pend on which segments of the fleet are affected. For ex-
ample, if future weight reductions occur in only the heaviest
of the light-duty vehicles, that can produce overall improve-
ments in vehicle safety. The following sections of the report
describe the committee's findings on vehicle weight, size,
and safety in greater detail and set forth some general con-
cerns and recommendations with regard to future efforts to
improve the fuel economy of the passenger vehicle fleet.
The Role of Vehicle Mass
The 1992 NRC fuel economy report concluded as fol-
lows: "Although the data and analyses are not definitive, the
Committee believes that there is likely to be a safety cost if
downweighting is used to improve fuel economy (all else
being equal)" (NRC, 1992, p. 6~. Studies continue to accu-
mulate indicating that mass is a critical factor in the injury
outcomes of motor vehicle crashes (e.g., Evans and Frick,
1992, 1993; Wood, 1997; Evans, 2001~. Although there are
arguments that not all increases in vehicle weight benefit
safety, these arguments do not contradict the general finding
that, all other things being equal, more mass is protective.
For example, Joksch et al. (1998) have reported that, when
vehicles of similar size are compared, those that are signifi-
cantly heavier than the average for their size do not appear to
improve their occupants' protection but do increase the risk
to occupants of other vehicles with which they collide. The
authors note (Joksch et al., 1998, p. ES-2) that this effect
should be interpreted with caution, because it is likely that
overweight vehicles are overweight in part because of more
OCR for page 71
IMPACT OF A MORE FUEL-EFFICIENT FLEET
powerful (and heavier) engines and performance packages,
which could attract more aggressive drivers. Thus, Joksch et
al. demonstrate that some weight increases can be detrimen-
tal to safety, but this finding does not change the basic rela-
tionship: among vehicles of equal size and similar driving
exposure, the heavier vehicle would be expected to provide
greater occupant protection.
The protective benefits of mass are clearly understood in
multiple-vehicle crashes, where the physical conservation of
momentum results in the heavier vehicle's experiencing a
smaller change in momentum, and hence lower occupant
deceleration, than the lighter vehicle. However, mass is also
protective in single-vehicle crashes with objects (such as
trees, poles, or guard rails), because many of these objects
will move or deform in proportion to the mass of the vehicle.
In this case, the change in velocity is not affected, but the
deceleration of the vehicle and its occupants decreases as the
object that is struck deforms or moves. Figures 4-7 and 4-8,
which show fatality rates per million registered vehicles by
vehicle type and vehicle weight, illustrate the protective ef-
fects of vehicle mass in single- and multiple-vehicle crashes.
The heaviest vehicles in each class (cars, SUVs, and pick-
ups) have about half as many fatalities per registered vehicle
as the lightest vehicles.)
While the benefits of mass for self-protection are clear,
mass can also impose a safety cost on other road users. In a
collision between two vehicles, increasing the mass of one
of the vehicles will decrease its momentum change (and the
forces on its occupants) but increase the momentum change
of the crash partner. Figure 4-9 shows the increased fatalities
caused in other vehicles per million registered cars, SUVs,
or pickups as the mass of the "striking" vehicle increases.
Because of this tendency to cause more injuries to occupants
of other vehicles, heavier vehicles are sometimes said to be
more "aggressive." Aggressivity also varies by vehicle type;
SUVs and pickups cause more deaths in other vehicles than
do passenger cars. There are also effects of vehicle type on
the likelihood of injuring pedestrians and other vulnerable
road users, although the effects of mass are much weaker
there (see Figure 4-10~. The smaller effect of mass for the
more vulnerable nonoccupants probably reflects the fact that
mass ratios between, for example, pedestrians and the light-
est vehicle are already so high that increasing mass of the
vehicle makes little additional difference in survivability for
the pedestrian. The differences by vehicle type may reflect
iBecause mass arid size are highly correlated, some of the relationships
illustrated in these figures are also attributable to differences in vehicle size,
an issue that will be discussed further later in this chapter. These figures
also show that mass is not the only vehicle characteristic affecting occupant
injury nsk, as there are substantial differences in occupant fatality risk for
cars, SUVs, and pickups of similar weight. Much of this difference prob-
ably results from the higher ride heights of SUVs and pickups; riding higher
is protective in multiple-vehicle crashes, because the higher vehicle tends to
override lower vehicles, but increases single-vehicle crash fatalities by rais-
ing the vehicle's center of gravity arid increasing rollover risk.
71
lo
lo
~ Cal
(A
.O
s
~ o
o ~
. _
. _
s
I
~ o
OKcars/passenger vans
O utility vehicles
| · pickups l
\\
\
<2500 2500- 3000- 3500- 4000- 4500- 5000+
vehicle weight (lb.)
FIGURE 4-7 Occupant death rates in single-vehicle crashes for
1990-1996 model passenger vehicles by weight of vehicle.
SOURCE: Insurance Institute for Highway Safety, using fatality
data from NHTSA's Fatality Analysis Reporting System (FARS)
for 1991-1997, a census of traffic fatalities maintained by NHTSA,
and vehicle registration data from the R.L. Polk Company for the
same years.
the greater propensity of taller vehicles to do more damage
in collisions with nonoccupants.
The net societal safety impact of a change in the average
mass of the light-duty vehicle fleet can be an increase, a
decrease, or no change at all. The outcome depends on how
that change in mass is distributed among the vehicles that
120
100
a' 80
s
o 60
20
\v
~' L
<2500 2500- 3000- 3500- 4000-
vehicle weight (lb.)
>1<cars/passenger vans
O utility vehicles
· pickups
it- - O O
4500- 5000+
FIGURE 4-8 Occupant death rates in two-vehicle crashes for
1990-1996 model passenger vehicles by weight of vehicle.
SOURCE: Insurance Institute for Highway Safety, using fatality
data from NHTSA's Fatality Analysis Reporting System (FARS)
for 1991-1997, a census of traffic fatalities maintained by NHTSA,
and vehicle registration data from the R.L. Polk Company for the
same years.
OCR for page 72
72
200
160
.o
o 1 20
to
. _
co
80
40
o
cars/passenger vans
O utility vehicles
· pickups
~
/1\
-
/
/.'
,
, \
~A\
\ /~A\
\v
/1\
-
/
<2500 2500- 3000- 3500- 4000- 4500- 5000+
vehicle weight (lb.)
FIGURE 4-9 Occupant death rates in other vehicles in two-vehicle
crashes for 1990-1996 model passenger vehicles. SOURCE: In-
surance Institute for Highway Safety, using fatality data from
NHTSA's Fatality Analysis Reporting System (FARS) for 1991-
1997, a census of traffic fatalities maintained by NHTSA, and ve-
hicle registration data from the R.L. Polk Company for the same
years.
make up the vehicle fleet (compare Appendix D of NRC,
1992).
In Chapter 2 the committee reviewed a 1997 study of the
National Highway Traffic Safety Administration (NHTSA)
(Kahane, 1997) that estimated the anticipated effect of a
100-lb change in the average weight of the passenger car and
light-truck fleets. These estimates indicated that such a
weight reduction would have different effects on different
crash types. Nevertheless, over all crash types, decreasing
the average weight of passenger cars would be expected to
increase the motor vehicle fatality risk (all else being equal).
Correspondingly, decreasing the average weight of the
heavier fleet of light trucks might reduce the motor vehicle
crash fatality risk (although the latter result was not statisti-
cally significant).
Lund and Chapline (1999) have reported similar findings.
They found that total fatalities in a hypothetical fleet of rela-
tively modern passenger vehicles would be reduced by about
0.26 percent if all pickups and SUVs weighing more than
4,000 lb were replaced with pickups and SUVs weighing
3,500 to 4,000 lb. However, if the heaviest cars, those weigh-
ing more than 3,500 lb, were replaced by cars weighing be-
tween 3,000 and 3,500 lb, the estimated effect changed to an
increase in total fatalities of 4.8 percent. Although the au-
thors did not consider crashes with nonoccupants such as
pedestrians and bicyclists, whose risk appeared to have no
clear relationship to vehicle mass (see Figure 4-10), the
results confirm Kahane's (1997) finding that the expected
EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS
50
40
.O
<~, 30
o
. _
._
~ 20
a)
s
Cal
10
o
>K\ ~
- \v
A\
aim
A\
>I<
/
~\
\
`\v
A\
>Kcars/passenger vans
O utility vehicles
· pickups
<2500 2500-
3000- 3500- 4000- 4500- 5000+
vehicle weight (lb.)
FIGURE 4-10 Pedestrian/bicyclist/motorcyclist death rates for
1990-1996 model passenger vehicles by vehicle weight. SOURCE:
Insurance Institute for Highway Safety, using fatality data from
NHTSA's Fatality Analysis Reporting System (FARS) for 1991-
1997, a census of traffic fatalities maintained by NHTSA, and ve-
hicle registration data from the R.L. Polk Company for the same
years.
societal effect of decreases in vehicle mass, whether in
response to fuel economy requirements or other factors, de-
pends on which part of the vehicle fleet becomes lighter.2
2As noted in Chapter 2, the committee has relied heavily on these NHTSA
analyses in its consideration of the likely effects of future improvements in
fuel economy. Although they have been the subject of controversy, the
committee's own review of the analyses found no compelling reasons to
change the conclusions or alter the estimates of the relationship between
vehicle mass and safety. Statistical and conceptual considerations indicate
that changes are occurring in the pattern of motor vehicle crash fatalities
and injuries, which could affect these estimates in the future, but the stabil-
ity of relative occupant fatality rates between lighter and heavier vehicles
over the past 20 years does not suggest that the estimates should change
significantly over the time period considered by the committee, essentially
the next 10-15 years (see Chapter 2). As indicated in Chapter 2, this com-
mittee believes that further study of the relationship between size, weight,
and safety is warranted, because of uncertainty about the relationship be-
tween vehicle weight and safety. However, the majority of the committee
believes that these concerns should not prevent the use of NHTSA's careful
analyses to provide some understanding of the likely effects of future im-
provements in fuel economy, if those improvements involve vehicle
downsizing. The committee believes this position is consistent with that of
the National Research Council's Transportation Research Board (NRC-
TRB) committee that reviewed the draft NHTSA report in 1996, which
concluded "it is important . . . to provide a sense of the range of uncertainty
so that policy makers and researchers can properly interpret the results"
(NRC-TAB, 1996, p. 7). NHTSA's final report has done that, and the use of
NHTSA's results is consistent with this committee's approach to other un-
certainties surrounding efforts to improve fuel economy: that is. to use the
best scientific evidence available to gauge likely effects and to state the
uncertainty associated with those efforts.
OCR for page 73
IMPACT OF A MORE FUEL-EFFICIENT FLEET
Vehicle Size and Safety
Estimates of the effect of vehicle weight have been con-
founded with the effects of size because the mass and size of
vehicles are correlated so closely. For example, the 2001
Buick LeSabre, a typical large car, is 200 inches long and 74
inches wide and weighs (unloaded) 3,600 lb. A 2001 four-
door Honda Civic, a typical small car for the United States,
has an overall vehicle length of 175 inches, overall width of
67 inches, and a weight of 2,400 lb (Highway Loss Data
Institute, 2001~. Thus, some of the negative effect of vehicle
weight constraints on safety that has been attributed to mass
reduction is attributable to size reduction.
Historical changes in the fleet have similarly confounded
mass and size characteristics. While the mass of the passen-
ger car fleet was decreased about 900 pounds between 1975
and 1990, the length of vehicles also declined, with average
wheelbase (the distance between the front and rear axles)
declining more than 9 inches (NRC, 1992~. Efforts to disen-
tangle these effects are hampered by the fact that, when ve-
hicles of similar size differ in mass, they usually do so for
reasons that still confound the estimate of mass effects (see,
for example, Joksch et al., 1998; C.J. Kahane, NHTSA, also
spoke of this in his presentation to the committee on Febru-
ary 6, 2001~.
Despite this confounding, carefully controlled research
has demonstrated that, given a crash, larger vehicles pro-
vide more occupant protection independent of mass. In
crashes between vehicles of similar mass, smaller vehicles
have higher fatality rates than larger ones (Evans and
Frick, 1992; Wood, 1997; Evans, 2001~. In addition,
Wood (1997) has argued that much of the apparent pro-
tective effect of mass in single-vehicle crashes may occur
because of the association of mass with size. Theoreti-
cally, increased size of one vehicle can be beneficial to
other road users as well, to the extent that the increased
size translates to more crush space (Ross and Wenzel,
2001; O'Neill, 1998~. By the same token, to the extent
that size reductions translate to less crush space, smaller
size is detrimental to both the vehicle's own occupants
and the occupants of other vehicles.
Theoretically, size can affect crash likelihood as well as
crashworthiness, independently of mass. For example, re-
ductions in size may make a vehicle more maneuverable.
Smaller vehicles may be easier to "miss" in the event of a
potential collision. Drivers of smaller, lower vehicles may
be better able to see and avoid other vulnerable road users
such as pedestrians and bicyclists. These effects could lead
to reduced societal risk despite the negative effects of re-
duced size on occupant protection, given a crash.
The committee found no direct empirical support for this
crash avoidance benefit, but there is some indirect support in
the pattern of Kahane's (1997) fatality results. For example,
Kahane reported a much larger reduction in pedestrian, bicy-
clist, and motorcyclist fatalities associated with a reduction
73
in light truck weights than with the same reduction in car
weights. The mass ratios between pedestrians and motor ve-
hicles are so large that the difference between cars and light
trucks cannot be due solely to the change in mass. Rather, it
is possible that some of the difference in reduction is due to
changes in size. and hence visibility of pedestrians, to the
driver. In addition, Kahane's analyses found no expected
change in car-to-car or truck-to-truck crash fatalities as a
result of vehicle downweighting. That result is contradictory
to other studies indicating that, in the event of a crash, smaller
cars offer less occupant protection (see above). The explana-
tion could be that a smaller vehicle's increased injury risk
given a crash is offset by a tendency to get into fewer crashes
(by virtue of its easier-to-miss, smaller profile or its poten-
tially superior agility).
The direct evidence that is available contradicts this crash
avoidance hypothesis, however. Overall, there is evidence
that smaller vehicles actually are involved in more collisions
than larger vehicles, relative to their representation in the
population of vehicles. The Highway Loss Data Institute
(HLDI) tracks the collision insurance claims experience of
about 65 percent of the vehicles insured in the United States.
Table 4-4 indicates the incidence of collision claims for
1998-2000 models in 1998-2000, relative to the average
collision claims frequency for all passenger cars. The results
have been standardized to represent similar proportions of
drivers less than 25 years of age. The principal pattern of
these data is that the frequency of collision claims is higher
for smaller vehicles, the opposite of what might be expected
from the simple geometry of the vehicles.
The important theoretical role of vehicle size for crash-
worthiness led the committee to consider whether some of
the adverse safety effects associated with decreases in mass
could be mitigated if size remained the same. In this context,
it is important to distinguish among different meanings of
the term "vehicle size." Changes in size of the occupant com-
partment are generally less relevant to safety (but not irrel-
evant) than changes in the exterior size of vehicles the lat-
ter affect the size of the so-called crush zones of the vehicle.
It is noteworthy that almost all of the downsizing that
occurred in conjunction with increased fuel economy oc-
curred in this crush zone; the size of the occupant compart-
TABLE 4-4 Relative Collision Claim Frequencies for
1998-2000 Models
Size Class
Four-Door
Cars
SUVs Pickups
Mini
Small
Midsize
Large
Very large
124
112
99
88
70
78 87
76
65
86
SOURCE: Highway Loss Data Institute (2001).
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74
EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS
meets of vehicles has changed little since 1977, when EPA
estimated the interior volume of cars to be 110 cubic feet.
That fell to a low of 104 cubic feet in 1980, but generally
ranged from 108 to 110 cubic feet during the l990s (EPA,
2000~. This reflects the critical effect of interior volume on
the utility of passenger cars and hence their marketability.
For the same reason, the committee expects that future size
reduction, if necessary to reduce weight, would again occur
principally outside the occupant compartment, and that inte-
rior space would be one of the last areas subject to reduction.
What would be the benefits if crush space were retained
in a future lighter-weight fleet? Empirical data do not exist
to answer this question quantitatively, but the committee
would expect a smaller adverse safety effect of vehicle
weight reduction. Still there would be some loss of occu-
pant protection, because lighter vehicles decelerate more
rapidly in crashes with other vehicles or with deformable
fixed objects. Effective crush space would therefore have
to increase with reductions in mass in order to keep injury
risk the same. Thus, if manufacturers try to maintain cur-
rent levels of occupant protection as they downweight, they
would have to use some of the weight savings from alter-
native materials and structures to provide additional crush
space.
In addition, it must be noted that not all the effects of
maintaining size will necessarily be beneficial. Some of the
increased risk of injury to occupants associated with vehicle
downweighting was offset by reduced injury risk to vulner-
able road users (Kahane, 1997~. Those offsetting benefits
may occur as a result of changes in certain size characteris-
tics that are typically associated with weight reduction. For
example, a change in the height and size of vehicle front
ends may be the critical factor in the estimated benefits to
pedestrians of reductions in the weight of light trucks. Thus,
if size is maintained, it may reduce the benefits of lighter-
weight vehicles for pedestrians and cyclists.
In sum, the committee believes that it will be important to
maintain vehicle crush space if vehicles are downweighted
in the future, but it is unable to develop quantitative esti-
mates of the extent to which such efforts can reduce the esti-
mated effects of vehicle downweighting.
Effect of Downweighting by Vehicle and Crash Type
To examine the impact of vehicle weight reduction on the
future safety environment, the majority of the committee
considered how weight reduction might influence various
crash types. This section of the report discusses how the com-
mittee expects vehicle weight reduction to operate in various
kinds of multivehicle and single-vehicle crashes.
Multiple-Vehicle Crashes
Multiple-vehicle crashes account for slightly more than
half of occupant fatalities. They include crashes between cars
and light trucks, crashes between either cars or light trucks
and heavy trucks, and crashes of cars with cars and light
trucks with light trucks. The effect on safety of down-
weighting and downsizing of the light-duty fleet varies
among these multiple-vehicle crash types:
Collisions Between Cars and Light Trucks Uniform down-
weighting of the fleet, that is, reducing weight from all
classes of vehicles, might be expected to produce an increase
in traffic casualties. However, if the downweighting is
restricted to the heaviest pickup trucks and SUVs, with no
weight reduction in the smaller light trucks or passenger cars,
casualties could decrease. Thus, for these crashes, any
change in casualties is very sensitive to how downsizing is
distributed. This is a consistent finding in the safety litera-
ture and is confirmed by the 1997 NHTSA analysis.
Collisions Between Light-Duty Vehicles and Heavy
Trucks If there is downsizing in any light-duty vehicles with
no corresponding change in heavy trucks, the number of ca-
sualties would increase. This finding is reflected in the 1997
NHTSA analyses and throughout the safety literature.
Collisions of Cars with Cars or Trucks with Trucks In
collisions of like vehicles of similar weight, a reduction in
both vehicle weight and size is expected to produce a small
increase in casualties. In fact, one consistent finding in the
safety literature is that as average vehicle weight declines,
crash risks increase (see Evans [2001], for example). The
laws of momentum do not explain this typical finding, but
analysts typically attribute it to the fact that as vehicle weight
declines, so does vehicle size. Narrowly defined studies fo-
cusing on pure crashworthiness consistently show this in-
crease. However, the 1997 NHTSA analysis, which exam-
ined the entire traffic environment, predicted a small
(statistically insignificant) decrease in fatalities. It has been
hypothesized that this inconsistency might be explained by
the greater maneuverability of smaller vehicles and, hence,
their involvement in fewer crashes. Studies have not found
this to be the case, but it is very difficult to fully normalize
data to account for the very complex traffic environment. In
this instance, the committee is unable to explain why the
1997 NHTSA analysis does not produce results consistent
with those in the safety literature. The rest of NHTSA's find-
ings regarding multivehicle crash types are consistent with
the literature.
Single-Vehicle Crashes
Single-vehicle crashes account for almost half of light-
duty vehicle occupant fatalities. As with multiple-vehicle
crashes, the safety literature indicates that as vehicle weight
and vehicle size decline, crash risks increase. The committee
examined three types of single-vehicle crashes: rollovers,
OCR for page 75
IMPACT OF A MORE FUEL-EFFICIENT FLEET
crashes into fixed objects, and crashes with pedestrians and
bicyclists.
Rollovers Historically, a large part of the increase in casual-
ties associated with vehicle downsizing has been attribut-
able to rollovers. As vehicles get shorter and narrower they
become less stable and their rollover propensity increases. If
the length and width of the vehicle can be retained as weight
is removed, the effect of weight reduction on rollover pro-
pensity can be reduced. However, unless track width wid-
ens, the vehicle's rollover propensity in actual use would
still increase somewhat, because occupants and cargo are
typically located above the vehicle's center of gravity (CG),
raising the vehicle's CG-height in use.
One Ford safety engineer noted in discussions with the
committee that the application of crash avoidance technol-
ogy (generically known as electronic stability control) that is
being introduced on some new vehicles might significantly
reduce vehicle rollovers. It is unknown at this time how ef-
fective this technology will be. In this regard, it is worth-
while noting the experience with other technology aimed at
reducing crash likelihood.
Antilock brakes were introduced on vehicles after exten-
sive testing indicated they unequivocally improved vehicle
handling in emergency situations. In fact, antilock brakes
were cited in the 1992 NRC report as a new technology that
might offset the negative effects of vehicle mass reductions
caused by increased fuel economy requirements (NRC, 1992,
p.59~. However, experience with antilock brakes on the road
has been disappointing. To date, there is no evidence that
antilock brakes have affected overall crash rates at all; the
principal effect has been to change the pattern of crashes
(Farmer et al., 1997; Farmer, 2001; Hertz et al., 1998~. Most
tellingly, the initial experience suggested that antilock brakes
actually increased fatal, single-vehicle, run-off-the-road
crashes and rollovers (Farmer et al., 1997), the very crashes
that the NRC committee thought antilock brakes might ben-
efit. Recent research suggests that this increase in fatal,
single-vehicle crashes associated with antilocks may be di-
minishing (Farmer, 2001), but still the evidence does not
permit a conclusion that antilocks are reducing crash risk.
Thus while it is conceivable that new technology might
reduce or eliminate the risk of rollovers, at this time the com-
mittee is not willing to change its expectations based on this
eventuality.
Fixed-Object Collisions Fixed-object collisions occur with
both rigid, unyielding objects and yielding objects that can
break or deform. For crashes into rigid objects, larger ve-
hicles will, on average, permit longer, lower decelerations,
although this will be influenced by the stiffness of the ve-
hicle. In crashes with yielding, deformable objects, as a
vehicle's weight is reduced, the struck object's deformation
is reduced, increasing the deceleration in the striking vehicle.
75
Thus lighter vehicles, with or without size reductions, would
be expected to increase occupant fatality risk.
Studies by Evans (1994), Klein et al. (1991), and Partyka
and Boehly (1989) all confirm that there is an inverse rela-
tionship between occupant safety and vehicle weight in these
crashes. Klein et al. found that there was a 10 percent in-
crease in fatality risk associated with a 1,000-lb reduction in
vehicle weight in single-vehicle, nonrollover crashes. Simi-
larly, NHTSA's 1997 analysis estimated that there is a
slightly greater than 1 percent increase in fatality risk associ-
ated with a 100-lb reduction in vehicle weight in these
crashes.3
Collisions with Pedestrians, Bicyclists, and Motorcyclists
If vehicles are downsized, they may be less likely to strike a
pedestrian, bicyclist, or motorcyclist. Further, should a colli-
sion occur, the reduced mass could lead to a reduction in
casualties, although, given the mismatch in the mass between
the vehicle and the unprotected road user, any benefit would
not be expected to be very large.
Safety Impacts of Possible Future Fuel
Economy Scenarios
The foregoing discussion provides the majority of the
committee's general views on how vehicle weight and size
reductions, if they occur in response to demands for in-
creased fuel economy, could affect the safety of motor ve-
hicle travel. The committee evaluated the likely safety ef-
fects of a number of possible scenarios involving different
amounts of downweighting of the future fleet, using the re-
sults of the NHTSA analyses (Kahane, 1997) for quantita-
tive guidance. Two of these possible scenarios are presented
below. They are not intended to reflect the committee's rec-
ommendations, but they do reflect two possibilities that can
be instructive in evaluating future fuel economy require-
ments. The first scenario examines the safety consequences
that would be expected if manufacturers achieved a 10 per-
cent improvement in fuel economy using the same pattern of
sin an attempt to gain more insight into single-vehicle crashes, Partyka
(1995) examined field data on single-vehicle, nonrollover crashes into yield-
ing fixed objects. Her goal was to learn if there was a relationship between
vehicle weight and crash outcomes. However, in this study, rather than
examining occupant injury as the crash outcome of interest, crash outcomes
were defined as whether the yielding object was damaged in the crash. For
frontal crashes she found that damage to the yielding fixed object was more
likely to occur in crashes with heavier vehicles. However, there was no
consistent relationship between vehicle weight and damage to the yielding
object in side crashes. The author was not able to consider crash severity as
a possible explanation for this anomaly since NHTSA's national accident
sampling system (NASS) did not provide estimates of crash severity for any
of the events where the yielding object was damaged. Further, the author
did not aggregate the data to reach an overall conclusion regarding the rela-
tionship between vehicle weight and damage to yielding fixed objects be-
cause she was uncomfortable with the results of the side impact analysis
and questioned its reliability (personal communication from the author).
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76
EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS
downweighting and downsizing that occurred in the late
1970s and 1980s. As discussed above, it is uncertain to what
extent downweighting and downsizing will be part of manu-
facturers' strategies for improving fuel economy in the fu-
ture, but one guide to their behavior can be to look at what
they did in the past.
The second scenario is based on the minimal weight
change predictions associated with the committee's cost-ef-
ficient analysis of future technology, discussed earlier in this
chapter. Thus, this analysis projects the safety consequences
if manufacturers apply likely powertrain technology prima-
rily to improve vehicle fuel economy.
In both scenarios, the hypothetical weight reductions are
based on the MY 2000 light-duty vehicle fleet (the average
car weighed 3,386 lb and the average light truck, 4,432 lb).
The estimated effects of the weight reductions are applied to
the 1993 vehicle fleet, the reference year for the NHTSA
analyses (Kahane,1997~. Obviously the results in these sce-
narios cannot be, nor are they intended to be, precise projec-
tions. NHTSA's analysis was based on the characteristics of
1985-1993 vehicles and was applied to the 1993 fleet. Fur-
ther, even if manufacturers dropped the average weight of
the vehicles described in the two scenarios starting in 2002,
it would take many years before those changes had any sig-
nificant influence on the overall makeup of the future ve-
hicle fleet. And that fleet would be operating in an environ-
ment that will differ from the environment that was the basis
for the 1997 NHTSA analysis.
Nevertheless, the committee's majority believes that the
calculations below provide some insight into the safety im-
pacts that might occur if manufacturers reduce weight in re-
sponse to increased fuel economy standards, as described
below.
Historical Pattern Scenario
Between 1975 and 1984, the average weight of a new car
dropped from 4,057 to 3,098 lbs (24 percent). For light
trucks, weight declined from 4,072 to 3,782, or 290 lb
(7 percent). These mass reductions suggest a 17 percent im-
provement in fuel economy for cars and a 5 percent improve-
ment for light trucks.4 During those years, the fuel economy
of cars and light trucks actually improved by about 66 per-
cent (from 15.8 mpg to 26.3 mpg) and 50 percent (from 13.7
mpg to 20.5 mpg), respectively. In other words, vehicle
downsizing accounted for about 25 percent of the improve-
ment in fuel economy of cars and 10 percent of the improve-
ment of light trucks between 1975 and 1984.
A similar pattern in achieving a 10 percent improvement
in fuel economy today would imply a 3.6 percent weight
reduction for cars (122 lb for 2000 models) and a 1.4 percent
4Based on an assumed 7 percent improvement in fuel economy for each
10 percent reduction in weight.
weight reduction for light trucks (63 lb for 2000 models).
Had this weight reduction been imposed on the fleet in 1993,
it would have been expected to increase fatalities involving
cars about 370 (+110) and to decrease fatalities involving
light trucks by about 25 (+40~. The net effect in 1993 for a
10 percent improvement in fuel economy with this mix of
downsizing and increased fuel efficiency would have been
about 350 additional fatalities (95 percent confidence inter-
val of 229 to 457~.
Cost-Efficient Scenario
Earlier in this chapter (under "Analysis of Cost-Efficient
Fuel Economy"), cost-efficient fuel economy increases of
12 to 27 percent for cars and 25 to 42 percent for light trucks
were estimated to be possible without any loss of current
performance characteristics. In the cost-efficient analysis,
most vehicle groups actually gain approximately 5 percent
in weight to account for equipment needed to satisfy future
safety standards. Thus, for these vehicle groups, cost-effi-
cient fuel economy increases occur without degradation of
safety. In fact, they should provide enhanced levels of occu-
pant protection because of both the increased level of safety
technology and the increased weight of that technology.
For three groups of vehicles (large cars, midsize SUVs,
and large SUVs), under the cost-efficient scenario, it is pro-
jected that manufacturers would probably compensate for
the added weight attributable to safety technology with
weight reductions in other areas. These weight reductions
mean that occupants of these vehicles are somewhat less pro-
tected in crashes than they otherwise would have been
(though they still benefit from the added safety technology).
Estimating the potential effect of this limited downsizing
is complicated because the estimates of the safety effect of
100-lb changes in average vehicle weight developed by
NHTSA cannot be applied directly to changes in specific
vehicle groups. However, NHTSA's report included sensi-
tivity analyses that estimated the effect of weight reductions
restricted to the heaviest 20 percent of cars (those heavier
than 3,262 lb) and to the heaviest 20 percent of light trucks
(those heavier than 3,909 lb) (Kahane, 1997, pp. 165-172~.
Specifically, NHTSA estimated that a 500-lb reduction in
these vehicle groups in 1993 would have resulted in about
250 additional fatalities in car crashes and about 65 fewer
fatalities in light-duty truck crashes.
If it is assumed that cars greater than 3,262 lb correspond
roughly to "large cars" as referred to in the committee's cost-
efficient fuel economy analysis outlined earlier in this chap-
ter, then the 5 percent weight reduction, had it occurred in
1993, would have been about 160 to 180 lb, or only about
one-third of the reduction of the NHTSA analysis. Thus, it is
estimated that reducing the weight of large cars in the way
foreseen in the cost-effective fuel economy analyses would
have produced about 80 additional fatalities in car crashes in
1993.
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IMPACT OF A MORE FUEL-EFFICIENT FLEET
Similarly, if midsize and large SUVs are assumed to be in
the heaviest 20 percent of light-duty trucks and if such ve-
hicles account for as much as half the light-duty truck popula-
tion in the near future, then about half the light-duty truck fleet
will be 5 percent lighter (about 200 lb). This weight reduction
is about 40 percent of the reduction studied by NHTSA and
would have saved 15 lives had it occurred in 1993.
Adding these effects yields an estimated increase of 80
car crash fatalities minus 15 fewer truck crash fatalities, or
about 65 additional fatalities.
NHTSA's sensitivity analysis did not include standard
errors for the weight reductions in the heaviest vehicles, but
in this case they would clearly be large enough that reason-
able confidence bounds for this estimate would include zero.
Thus, an increase in fatality risk in the future fleet is pre-
dicted from the kinds of weight reductions included in the
cost-efficient fuel economy scenario identified by the com-
mittee, but the uncertainty of this estimate is such that the
effect might be zero and would be expected to result in fewer
than 100 additional fatalities.
In addition, it should be noted that these results do not
imply that the actual safety effect would be as small as this
if the required fuel economy rises to the targets indicated in
the cost-efficient analyses. This is because manufacturers
could choose to use advances in drive train technology for
other vehicle attributes such as acceleration or load capac-
ity. In that case, additional vehicle downweighting might
occur, and the adverse safety consequences would grow.
Thus, the actual safety implications of increasing fuel
economy to the cost-efficient levels specified earlier in this
chapter will depend on what strategies manufacturers actu-
ally choose in order to meet them and the structure of the
regulatory framework.
Conclusion: Safety Implications of Increased CAFE
Requirements
In summary, the majority of the committee finds that the
downsizing and weight reduction that occurred in the late
1970s and early 1980s most likely produced between 1,300
and 2,600 crash fatalities and between 13,000 and 26,000
serious injuries in 1993. The proportion of these casualties
attributable to CAFE standards is uncertain. It is not clear
that significant weight reduction can be achieved in the fu-
ture without some downsizing, and similar downsizing
would be expected to produce similar results. Even if weight
reduction occurred without any downsizing, casualties would
be expected to increase. Thus, any increase in CAFE as cur-
rently structured could produce additional road casualties,
unless it is specifically targeted at the largest, heaviest light
trucks.
For fuel economy regulations not to have an adverse im-
pact on safety, they must be implemented using more fuel-
efficient technology. Current CAFE requirements are neu-
77
tral with regard to whether fuel economy is improved by
increasing efficiency or by decreasing vehicle weight. One
way to reduce the adverse impact on safety would be to es-
tablish fuel economy requirements as a function of vehicle
attributes, particularly vehicle weight (see Chapter 5~. An-
other strategy might be to limit horsepower-to-weight ratios,
which could save fuel by encouraging the application of new
fuel efficiency technology for fuel economy rather than
performance.
The committee would also like to note that there is a re-
markable absence of information and discussion of the speed
limit in the context of fuel consumption. The national 55-
mph speed limit that was in effect until 1987 is estimated to
have reduced fuel consumption by 1 to 2 percent while si-
multaneously preventing 2,000 to 4,000 motor vehicle crash
deaths annually (NRC, 1984~. Relaxation of the speed limit
has increased fatalities in motor vehicle crashes (Baum et
al., 1991; Farmer et al., 1999), and fuel consumption pre-
sumably is again higher than it would have been. In addition,
it is reasonable to expect that higher speed limits, combined
with higher fuel efficiency, provide incentives for driving
further and faster, thereby offsetting intended increases in
fuel economy, though this hypothesis is speculative on the
part of the committee.
But the committee wants to close where it started, by con-
sidering the effect of future advances in safety technology
on CAFE. Despite the adverse safety effects expected if
downweighting occurs, the effects are likely to be hidden by
the generally increasing safety of the light-duty vehicle fleet.
This increase in safety is driven by new safety regulations,
testing programs that give consumers information about the
relative crash protection offered by different vehicles, and
better understanding of the ways in which people are injured
in motor vehicle crashes. Alcohol-impaired driving has been
decreasing and seat belt usage has been increasing. Roads
are becoming less hazardous for vehicles.
Some might argue that this improving safety picture
means that there is room to improve fuel economy without
adverse safety consequences. However, such a measure
would not achieve the goal of avoiding the adverse safety
consequences of fuel economy increases. Rather, the safety
penalty imposed by increased fuel economy (if weight re-
duction is one of the measures) will be more difficult to iden-
tify in light of the continuing improvement in traffic safety.
Just because these anticipated safety innovations will im-
prove the safety of vehicles of all sizes does not mean that
downsizing to achieve fuel economy improvements will have
no safety costs.
If an increase in fuel economy is effected by a system that
encourages either downweighting or the production and sale
of more small cars, some additional traffic fatalities would
be expected. Without a thoughtful restructuring of the pro-
gram, that would be the trade-off that must be made if CAFE
standards are increased by any significant amount.
OCR for page 78
78
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Farmer, C.M. 2001. New Evidence Concerning Fatal Crashes of Passenger
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Farmer, C.M., R.A. Retting, and A.K. Lund. 1999. "Changes in Motor Ve-
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Greene, D.L. 2001. Cost-Efficient Economy Analysis. Draft. Prepared for
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7 7 "'
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OCR for page 79
Attachment 4A
Life-Cycle Analysis of Automobile Technologies
Assessments of new automobile technologies that have
the potential to function with higher fuel economies and
lower emissions of greenhouse gases (GHGs) have been
made by the Energy Laboratory at the Massachusetts Insti-
tute of Technology (MIT) (Weiss et al., 2000) and by the
General Motors Corporation (GM), Argonne National Labo-
ratory, BP, ExxonMobil, and Shell (General Motors et al.,
2001, draft). Both studies compared fuels and engines on a
total systems basis, that is, on a well-to-wheels (WTW) ba-
sis. These assessments provide an indication of areas of
promising vehicle and fuel technology and benchmarks for
likely increases in fuel economy and reduction of GHG emis-
sions from the light-duty fleet over the next two decades.
This attachment provides additional information on the
emerging technologies and GHG emissions described in
Chapters 3 and 4.
MIT's analysis was confined to midsize cars with con-
sumer characteristics comparable to a 1996 reference car
such as the Toyota Camry. It was assumed that, aided by the
introduction of low-sulfur fuels, all technologies would be
able to reduce emissions of air pollutants to levels at or be-
low federal Tier 2 requirements. Only those fuel and vehicle
technologies that could be developed and commercialized
by 2020 in economically significant quantities were evalu-
ated. General Motors et al. (2001) focused on the energy use
of advanced conventional and unconventional power-train
systems that could be expected to be implemented in the
2005 to 2010 time frame in a Chevrolet Silverado full-size
pickup truck. The technologies were assessed on the basis of
their potential for improving fuel economy while maintain-
ing the vehicle performance demanded by North American
consumers. Vehicle architectures and fuels analyzed in both
studies are listed in Table 4A-1.
In the MIT study, the vehicle lifetimes and driving dis-
tances were assumed to be similar for all vehicles. The more
advanced technologies were compared to an "evolved
baseline" vehicle a midsize passenger car comparable in
consumer characteristics to the 1996 reference car, in which
fuel consumption and GHG emissions had been reduced by
about a third by 2020 through continuing evolutionary im-
provements in the traditional technologies currently being
used. Figure 4A-1 summarizes energy use, GHG emissions,
and costs for all the new 2020 technologies relative to the
1996 reference car and the evolved 2020 baseline car. (The
battery-electric car shown is an exception in that it is not
"comparable" to the other vehicles; its range is about one-
TABLE 4A-1 Vehicle Architecture and Fuels Used in the MIT and General Motors et al. Studies
MIT (Weiss et al., 2000)
General Motors et al. (2001)
1996 reference internal combustion engine (ICE)
Baseline evolved ICE
Advanced gasoline ICE
Gasoline ICE hybrid vehicle (HEY)
Diesel ICE hybrid
CNG ICE hybrid
Gasoline fuel cell (FC) hybrid vehicle
Methanol FC hybrid
Hydrogen FC hybrid
Battery electric
Conventional (CONY) with spark ignition (SI) gasoline engine (baseline) [GASO SI CONY]
CONV with SI E85 (85% ethanol and 15% gasoline by volume) engine [HESS SI CONY]
CONV with compression-ignition direct-injection (CIDI) diesel engine [DIESEL CIDI CONY]
Charge-sustaining (CS) parallel hybrid electric vehicle (HEY) with SI E85 engine [HE 85 SI HEV]
CS HEV with CIDI diesel [DIESEL CIDI HEV]
Gasoline fuel processor (FP) fuel cell vehicle (FCV) [GASO FP FC FCV]
Gasoline (naphtha) FP fuel cell (FC) HEV [NAP FP FC HEV]
Gaseous hydrogen (GH2) refueling station (RS) FC HEV [GH2 RS FC HEV]
Methanol (MeOH) FP FCV [MEOH FP HEV]
Ethanol FP FC HEV [HEV 100 FP FC HEV]
79
OCR for page 80
80
EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS
TECHNOLOC;Y
1996 Reference ICE
Baseline evolved ICE
Advanced gasoline ICE
Advanced diesel ICE
Gasoline ICE hybrid
Diesel ICE hybrid
CNG ICE hybrid
Gasoline FC hybrid
Methanol FC hybrid
Hydrogen FC hybrid
Battery electric
TECHNOLOGY
1996 Reference ICE
Baseline evolved ICE
Advanced gasoline ICE
Advanced diesel ICE
Gasoline ICE hybrid
Diesel ICE hybrid
CNG ICE hybrid
Gasoline FC hybrid
Methanol FC hybrid
Hydrogen FC hybrid
Battery electric
TECHNOLOGY
1996 Reference ICE
Baseline evolved ICE
Advanced gasoline ICE
A - lanced diesel ICE
Gasoline ICE hybrid
Diesel ICE hybrid
CNG ICE hybrid
Gasoline FC hybrid
Methanol FC hybrid
Hydrogen FC hybrid
Battery electric
ENERGY
.. At- , ~
,-
t
0 50 100 150 200
Relative L~6e-Cyclc Energy Use
GREENIlO\JSE GAS EMISSIONS
1
_ _
0 50 log 150 200
Relative Life-Cyclc GHC Emissions
cosr
~ 1
l ~ _
_ ~ l
_ _
0 50 10O 150 200
Relative Total Cost/kn' for New Car Customers
FIGURE 4A-1 Life-cycle comparisons of technologies for midsize passenger vehicles. NOTE: All cars are 2020 technology except for the
1996 reference car. On the scale, 100 = 2020 evolutionary baseline gasoline ICE car. Bars show estimated uncertainties. SOURCE: Weiss
et al. (2000~.
OCR for page 81
IMPACT OF A MORE FUEL-EFFICIENT FLEET
third less than that of the other vehicles.) The bars suggest
the range of uncertainty surrounding the results. The uncer-
tainty is estimated to be about +30 percent for fuel-cell and
battery vehicles, +20 percent for hybrid electric vehicles
(HEVs) using internal combustion engines (ICE), and +10
percent for all other vehicle technologies.
MIT concludes that continued evolution of the tradi-
tional gasoline car technology could result in 2020 vehicles
that reduce energy consumption and GHG emissions by
about one-third relative to comparable vehicles of today at
a cost increment of roughly 5 percent. More advanced tech-
nologies for propulsion systems and other vehicle compo-
nents could yield additional reductions in life-cycle GHG
emissions (up to 50 percent lower than those of the evolved
baseline vehicle) at increased purchase and use costs (up to
about 20 percent greater than those of the evolved baseline
vehicle). Vehicles with HEV propulsion systems using ei-
ther ICE or fuel-cell power plants are the most efficient and
lowest-emitting technologies assessed. In general, ICE
HEVs appear to have advantages over fuel-cell HEVs with
respect to life-cycle GHG emissions, energy efficiency, and
vehicle costs, but the differences are within the uncertain-
ties of MIT's results and depend on the source of fuel en-
ergy. If automobile systems with drastically lower GHG
emissions are required in the very long run future (perhaps
in 30 to 50 years or more), hydrogen and electrical energy
are the only identified options for "fuels," but only if both
are produced from nonfossil sources of primary energy
14000 _
81
(such as nuclear or solar) or from fossil primary energy
with carbon sequestration.
The results from the General Motors et al. study (2001)
are shown in Figures 4A-2 and 4A-3. The diesel compres-
sion-ignition direct-injection (CIDI)/HEV, gasoline and
naphtha fuel-processor fuel-cell HEVs, as well as the two
hydrogen fuel-cell HEVs (represented only by the gaseous
hydrogen refueling station and fuel-cell HEV in Figure 4A-
2) are the least energy-consuming pathways. All of the crude-
oil-based selected pathways have well-to-tank (WTT) en-
ergy loss shares of roughly 25 percent or less. A significant
fraction of the WTT energy use of ethanol is renewable. The
ethanol-fueled vehicles yield the lowest GHG emissions per
mile. The CIDI HEV offers a significant reduction of GHG
emissions (27 percent) relative to the conventional gasoline
spark-ignitied (S I) vehicle .
Considenng both total energy use and GHG emissions,
the key findings by General Motors et al. (2001) are these:
Of all the crude oil and natural gas pathways studied,
the diesel CIDI hybrid electric vehicle (HEV), the
gasoline and naphtha HEVs, and the gaseous hydro-
gen fuel-cell HEVs were nearly identical and best in
terms of total system energy use. Of these technolo-
gies, GHG emissions were expected to be lowest for
the gaseous hydrogen fuel-cell HEV and highest for
the diesel CIDI HEV.
· The gasoline-spark-ign~ted HEV and the diesel CIDI
12~
10000
8000
-
6000
2000
O
-t ~
. . ~ .
,
. ~ ~
. . . .
DIESEL T GASO | NAP T GH2 AS | PEON | HE1 -
CIDI HEV FP FC HEV FP FC HEV FC HEV FP FC HO FP FC HO
GASO HESS DIESEL i HESS
Sl CONV Sl CONV CIDI CONS I Sl HO
FIGURE 4A-2 Well-to-wheels total system energy use for selected fuel/vehicle pathways. SOURCE: General Motors et al. (2001~.
OCR for page 82
82
EFFECTIVENESS AND IMPACT OF CORPORATE AVERAGE FUEL ECONOMY (CAFE) STANDARDS
Boo
SON -
~oo
Boo
200
o _
~ f
t
Gum HE8S DIESEL H~
SI CONV Sl CONV C101 CONE Sl HEV
.
DIESEL GASO N" GH2 RS IdIEOH H~.
CIDI HEV FP fC HEV PP FC HO FC HO ~ FC H~ ~ FC HO
FIGURE 4A-3 Well-to-wheels greenhouse gas emissions for selected fuel/vehicle pathways. SOURCE: General Motors et al. (2001~.
.
HEV, as well as the conventional CIDI diesel, offer
significant total system energy use and GHG emission
benefits compared with the conventional gasoline
engine.
· The methanol fuel-processor fuel-cell HEV offers no
significant energy use or emissions reduction advan-
tages over the crude-oil-based or other natural-gas-
based fuel cell HEV pathways.
· Bioethanol-based fuel/vehicle pathways have by far
the lowest GHG emissions of the pathways studied.
Major technology breakthroughs are required for both
the fuel and the vehicle for the ethanol fuel-processor
fuel-cell HEV pathway to reach commercialization.
· On a total system basis, the energy use and GHG em~s-
sions of compressed natural gas and gasoline spark-
ignited conventional pathways are nearly identical.
(The compressed natural gas [CNG] pathway is not
shown in Figures 4A-2 or 4A-3.
· The crude-oil-based diesel vehicle pathways offer
slightly lower system GHG emissions and consider-
ably better total system energy use than the natural-
gas-based Fischer-Tropsch diesel fuel pathways. Cri
teria pollutants were not considered.
Liquid hydrogen produced in central plants, Fischer-
Tropsch naphtha, and electrolysis-based hydrogen
fuel-cell HEVs have slightly higher total system en-
ergy use and the same or higher levels of GHG em~s-
sions than gasoline and crude naphtha fuel-processor
fuel-cell HEVs and electrolytically generated hydro-
gen fuel-cell HEVs.
REFERENCES
General Motors Corporation, Argonne National Laboratory, BP, Exxon
Mobil and Shell. 2001. Wheel-to-Well Energy Use and Greenhouse Gas
Emissions of Advanced Fuel/Vehicle Systems. North American Analy-
sis, April. Final draft.
Weiss, Malcolm A., John B. Heywood, Elisabeth M. Drake, Andreas
Schafer, and Felix F. AuYeung. 2000. On the Road in 2020: A Life-
Cycle Analysis of New Automobile Technologies. Energy Laboratory
Report # MIT EL 00-003, October. Cambridge, Mass.: Massachusetts
Institute of Technology.
Representative terms from entire chapter:
ghg emissions
