2 equivalent/yr)
Full-Cycle Emission Accounting
Light vehicle, Ledbetter and Ross
-52
-50
-46
-2
379
Light vehicle, Shackson and Leach
-10
-1
+10
+191
389
Light vehicle, Difiglio
-26
-22
-13
+128
397
Heavy truck
-42
-38
-32
+45
61
Aircraft retrofit
+230
13
Consumption Emission Accounting
Light vehicle, Ledbetter and Ross
-81
-78
-71
-3
245
Light vehicle, Shackson and Leach
-16
-2
+16
+296
251
Light vehicle, Difiglio
-40
-34
-20
+198
256
Heavy truck
-65
-59
-50
+70
39
Aircraft retrofit
+357
8
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Land use planning strategies that local governments and planners
can use to manage travel demand include requiring land use plans
and zoning to be consistent with transportation capacity, planning
future development densities to accommodate present and future
transportation capacity, and restricting uses that generate
excessive numbers of trips (Deakin, 1989). Another set of
regulatory approaches focuses on reducing trips associated with new
developments by requiring developers to meet certain site design
criteria, provide for transportation and other infrastructure, and
comply with trip reduction ordinances (Suhrbier and Deakin, 1988).
The Southern California Association of Governments (SCAG) has
proposed one of the most far-reaching land-use-oriented TDM
programs—the redistribution of some population growth into
job-rich areas and some jobs growth into housing-rich areas in
order to promote jobs/housing balance (Southern California
Association of Governments, 1989).
Employer-based TDM programs have successfully changed commuting
behavior and reduced the use of single-occupant vehicles. A recent
survey by the Federal Highway Administration concluded that TDM
programs, especially when undertaken in conjunction with parking
management programs, should normally be able to achieve trip
reductions in the range of 20 to 40 percent (U.S. Department of
Transportation, Federal Highway Administration, 1990). TDM programs
can be even more effective if they address some of the reasons
commuters prefer to drive (e.g., the need to leave children at day
care and concern that the car may be needed during the day for
emergencies) through methods such as provision of day care at the
work site and guaranteed ride home programs for emergencies (U.S.
Department of Transportation, Urban Mass Transportation
Administration, 1989a; U.S. Department of Transportation, Federal
Highway Administration, 1990).
The cost of TDM programs varies widely depending on the measures
used, the size of the employer, and other factors. Costs are
frequently in the range of $15 to $55 per employee, but may be as
high as $100 per employee per year (Municipality of Metropolitan
Seattle, Service Development Division, 1989; U.S. Department of
Transportation, Urban Mass Transit Administration, 1989a).
Using TDM to increase average vehicle occupancy could be a
cost-effective way of reducing CO2
emissions. In the United States the average occupancy level of
commuter vehicles is only 1.1 persons per vehicle. If this could be
increased to 2.1 persons per vehicle, 30 to 40 million gallons of
gasoline would be saved daily (American Public Transit Association,
1989). While increasing the peak-hour vehicle occupancy rate to 2.1
persons per vehicle would be a daunting (some would say impossible)
task, achieving this long-term goal would result in an annual
CO2 reduction of 98 to 131 Mt. Even
if the TDM costs needed to achieve this goal are as high as $100
per employee per year for each of the 96.7 million workers in the
United States (Pisarski, 1987), the offsetting gasoline savings of
$10.95 billion per year ($1/gallon for 30 million gallons/day)
would eliminate 98 Mt of CO2
emissions at a cost of -$13/t.
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High-Occupancy-Vehicle Lanes
Pricing measures, parking management, and transportation demand
management are all designed at least in part to increase average
vehicle occupancy during peak commuting hours. One way of
accommodating the increased number of multioccupant vehicles would
be to increase the supply of specially designated
high-occupancy-vehicle (HOV) lanes. Such lanes are built for the
exclusive use of buses, vanpools, and (sometimes) carpools carrying
three or more persons.
In recent years, construction of HOV lanes has gained acceptance
as an effective means of reducing commuting time, encouraging
ridesharing, and increasing vehicle occupancy rates (Southern
California Association of Governments, 1989). HOV lanes can reduce
commuting time on congested highways by 45 to 50 percent and also
reduce the total VMT (Davis et al., 1989; Institute of
Transportation Engineers, 1988). The Institute of Transportation
Engineers has concluded that HOV lanes are often the lowest-cost
type of fixed transit facility, with benefit-cost ratios in excess
of 6 (Institute of Transportation Engineers, 1988, 1989). Despite
these advantages, HOV lanes—especially when converted from
existing general-purposes lanes—have met with political
opposition from drivers upset by the sight of seemingly unused
capacity in the more free-flowing HOV lanes.
High-occupancy-vehicle lanes often cost far less than equal
amounts of new highway capacity because each HOV lane (both at and
well before the point at which the incentive to drive in the lane
reaches zero) carries more persons than a regular highway lane.
Costs generally range from $30,000 to $2 million per lane-mile when
existing lanes are converted to HOV lanes and from $4 to $8 million
per lane-mile when HOV facilities are constructed in existing or
separate rights of way (Turnbull and Hanks, 1990).
Other Benefits and Costs
By reducing fuel use, vehicle use, and traffic congestion,
transportation system management measures produce a variety of
benefits in addition to CO2 emission
reductions. These include reducing dependence on imported oil,
lowering emissions of conventional and toxic air pollutants, and
avoiding productivity losses from delays in the movement of goods
and people. These benefits may total tens of billions of dollars.
At the same time, there are costs—including potential consumer
welfare losses from required life-style changes—incurred in
adopting transportation demand measures.
Reducing transportation energy use could significantly improve
the U.S. balance of trade and energy security position. The
transportation sector accounts for approximately two-thirds of all
U.S. oil use, an amount greater than that produced domestically
(Davis et al., 1989). The direct costs of
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importing petroleum products account for nearly 40 percent of
the U.S. trade deficit. The United States incurs other costs
because of this dependence on imported oil, including those related
to using the military to protect strategic supply regions,
maintaining the Strategic Petroleum Reserve, and living with the
risk of supply disruptions. These costs have been estimated at
between $21 billion and $125 billion annually (Greene et al.,
1988), or $7 to $40 for each of the 8.3 million barrels of oil
imported daily during the first four months of 1990.
Reducing VMT will reduce emissions of air pollutants, for which
permissible standards are set in terms of grams of pollutant
emitted per mile. The transportation sector, particularly light
trucks and automobiles, is responsible for a large proportion of
U.S. air pollution, particularly in urban areas. Motor vehicles
emit five of the six "criteria" pollutants regulated under the
Clean Air Act, including fine particulates and
• 70 percent of CO;
• 40 percent of volatile organic compounds, which are
precursors to the formation of ozone, the primary component of
urban smog;
• 40 percent of NOx,
regulated pollutants that are precursors to both acid rain and
photochemical air pollution; and
• 35 percent of lead, a potent neurotoxin particularly
dangerous to young children (MacKenzie, 1988; U.S. Office of
Technology Assessment, 1989). Motor vehicles are also responsible
for a variety of toxic emissions (especially benzene and
formaldehyde) from exhaust and gasoline vapors, all of which also
could be reduced by greenhouse gas mitigation measures.
Air pollution adversely affects human health and the
environment. Estimates of the total societal cost of pollutant
emissions from refineries, fueling stations, and motor vehicles
range from $11 billion to $187 billion annually, depending on
assumptions about both the numbers of deaths and illnesses and the
monetary value assigned to the loss of life (Greene et al.,
1988).
Another benefit of transportation system management is that
measures limiting the number of VMT or reducing the degree of
congestion encountered while traveling avoid substantial
productivity losses from delays in the movement of goods and
people. National estimates of delay on urban highways and resulting
productivity losses have been prepared by the Federal Highway
Administration and reviewed by the General Accounting Office. In
1987, highway delays cost motorists $7.8 billion in wasted time. By
2005 the cost of delays is projected to increase to $29 billion to
$43 billion. Another type of lost productivity is the cost of
delaying trucks carrying goods. The Federal Highway Administration
has estimated that the total annual cost of truck delay on highways
alone is $4.2 billion to $7.6 billion; additional trucking
productivity losses from congestion on urban
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streets would add $19.4 billion to $22.9 billion to this total
(U.S. General Accounting Office, 1989).
These estimates of $52.6 billion to $73.5 billion in annual
productivity losses at current congestion levels do not include
delays faced by commuters on local streets or the costs of
tardiness to employers. When surveyed, employers frequently cite
reductions in tardiness and absenteeism as reasons for sponsoring
ridesharing programs. One survey of 20 such programs found that 18
of 20 ridesharing programs had cost-benefit ratios greater than 1
when the benefits of reduced tardiness, absenteeism, and need to
construct parking facilities were calculated; cost-benefit ratios
were frequently in excess of 10 (Wegmann, 1989).
Despite these benefits, there are costs—primarily in the
form of consumer welfare losses—that will likely occur due to
efforts to reduce solo commuting and vehicle usage. For many
workers, commuting could take longer and result in lost
productivity. A typical mass transit commute in the United States
averages 13 to 14 mph, whereas commuters driving alone or in a
carpool travel at 31.5 to 33.5 mph while covering a comparable
distance (Pisarski, 1987). (Although such losses cannot be
quantified, commuters and other drivers will also suffer "consumer
welfare" losses from real or perceived reductions in personal
mobility and freedom.)
These consumer welfare losses can, however, be minimized by
focusing transportation system management efforts on reducing
commuters' travel time. Transit can be made more convenient and
faster; HOV lanes can be used to reduce travel time for buses,
vanpools, and carpools. Differences in commuting time between
automobiles and other modes will also narrow if congestion
increases automobile travel times: average vehicle speeds in
southern California are projected to fall to 19 mph in the absence
of transportation system management (Southern California
Association of Governments, 1989). In addition, behavioral studies
indicate that commuters are more concerned about travel time
reliability than total elapsed travel time (Wachs, 1989); thus
minimizing variations in travel time on mass transit and in the use
of HOV lanes should reduce consumer welfare losses.
Research and Development Needs
The research and development needs for each of the three primary
mitigation options described above are listed in this section.
Recently, the National Research Council's (1990) alternative energy
research and development study made the following
recommendations:
• Improve batteries for vehicle propulsion to achieve
higher performance and durability and to reduce costs.
• Adapt alternative fuels (e.g., alcohols) to engines and
vehicles.
• Reduce emissions from efficient power plants such as the
diesel.
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• Evaluate vehicle systems to ensure the safety of smaller
cars built with lightweight structural materials.
• Investigate innovative electric transportation
systems.
The Mitigation Panel would also include hydrogen in the list of
alternative fuels that need to be adapted to current engines and
vehicles and would note that the focus of these alternative fuel
efforts should be generation of fuels (such as methanol) from
sources such as biomass and nonfossil electricity that do not
increase greenhouse gas emissions. Since the method by which
primary energy is generated is such an important factor in
alternative transportation fuels, a number of research and
development recommendations in the energy supply sector (see
Chapter 24) are also applicable here.
Transportation system management has, to date, been a largely
empirical exercise—governments and private employers put
measures into effect and only subsequently evaluate which work or
why. Surveys, pilot programs, and other research tools should be
used to predict and evaluate which methods are most effective in
altering transportation behavior. In particular, the relative
efficacy of different pricing mechanisms—gasoline taxes,
parking fees, tolls, sales taxes, and registration fees—should
be evaluated (Deakin, 1990; Hillsman and Southworth, 1990).
Conclusions
The transportation sector accounts for 30 percent of CO2 emissions. Changes in transportation
over the next several decades could substantially affect the
nation's contributions to greenhouse warming. Moreover, such
changes are likely to influence practices elsewhere as well. For
these reasons, a focus on transportation is an important component
of policy.
Of the three different types of methods for reducing greenhouse
gas emissions from the transportation sector, vehicle efficiency
has the greatest potential. However, implementation of vehicle
efficiency measures will be slow because of the low turnover of
vehicles in the marketplace and the time delay between design and
production of vehicles.
Each of the alternative transportation fuels has problems.
Biomass fuels require production systems and infrastructures not
currently available. In addition, there is concern about the
ability to convert sufficient land to grow corn for ethanol or
woody biomass for methanol or ethanol.
For hydrogen, the production systems and infrastructure would
have to be created. There are storage and safety concerns to be
resolved for vehicles having on-board reservoirs of hydrogen. If
hydrogen is to be used to reduce greenhouse gas emissions, it must
be made by using nonfossil-fuel-generated energy.
Electric vehicles are a viable option only if the electricity is
produced from nonfossil fuels. Further technological advances,
particularly with batteries,
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but probably also involving the electrical charging
infrastructure, are needed to produce electric vehicles that will
be as convenient to use as today's fossil-fuel-powered
vehicles.
If alternative fuels are to serve as a significant alternative
to gasoline in the next century, the federal government will have
to both increase funds for research and development programs and
tax gasoline to reflect its full social costs and make alternative
fuels cost-competitive. In the interim, alternative fuels should
not be used if the switch from gasoline increases life-cycle carbon
emissions.
In the area of transportation system management, supply-side
measures such as providing HOV lanes and increasing mass transit
capacity—and demand-side measures involving pricing, parking
availability, and transportation demand management—can
cost-effectively and substantially reduce vehicle miles traveled,
traffic congestion, fuel use, and CO2 emissions. One particularly attractive
feature of transportation demand management is that CO2 emission reductions could occur during
the period when fuel economy changes are being phased in; these
measures will also protect fuel economy improvements in the longer
term. To gain these benefits, barriers such as inappropriate
transportation pricing and lack of alternatives must be overcome.
In addition, steps must be taken to reduce potential consumer
welfare losses due to increases in commuting time and reductions in
personal freedom. Transportation system management has the
potential, however, to be a cost-effective CO2 reduction strategy for small amounts of
CO2 reduction while fulfilling its
primary goal of providing mobility for people at the least total
cost to society.
Major uncertainties stand in the way of large-scale reductions
in greenhouse gas emissions from transportation. Several are
discussed here because they are especially important to U.S.
national policy:
• Uncertainty over the degree of willingness of vehicle
owners (households and firms) to purchase smaller, more
fuel-efficient vehicles when fuel prices are low poses a
significant barrier to the adoption of more fuel-efficient
vehicles. Ways of overcoming this barrier while preserving the
dynamics of competition in the U.S. vehicle market will have to be
identified, evaluated, and implemented.
• Policies aimed at altering vehicle use, including fuel
pricing, transportation demand management, and changes in urban
design, also face large uncertainties. Promising attempts are
beginning in southern California, motivated by concern over air
quality. Careful monitoring and deliberate experimentation in this
and other metropolitan areas could yield important findings over
the next decade.
Perhaps the largest uncertainty is the degree to which consumers
and voters will be willing to respond to changing price and policy
signals by
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buying more fuel-efficient cars, changing commuting patterns,
and otherwise altering their life-style. One should bear in mind
that the emergence of current vehicle use patterns in
industrialized societies occurred over the last half-century, a
time span comparable with that in which greenhouse warming may
occur.
Notes
1. Throughout this report, tons (t) are metric; 1 Mt = 1 megaton
= 1 million tons; and 1 Gt = 1 gigaton = 1 billion tons.
2. Subsequent to the preparation of these results, K. G. Duleep
(co-author with Difiglio and Greene) has refined the estimate of
the ''maximum technology" point. Duleep estimates that in 1996 all
available technologies could produce a CAFE mpg of 29.3 (22.5
on-road) and in 2001 all available technologies could produce a
CAFE mpg of 36.0 (27.7 on-road) (Plotkin, 1991).
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Representative terms from entire chapter:
greenhouse gas
FIGURE 23.1 Fuel economy trends. The fuel
economy index (FEI) is an index of
powertrain efficiency, the product of vehicle mass and fuel
economy.
SOURCE: Data are
from Amann (1989).
FIGURE 23.2 Components of change in light-duty
vehicles.
SOURCE: U.S.
Department of Energy (1989).
weight, improving vehicle aerodynamics, and reducing the
tire-rolling resistance.Each of these methods and their cost are
discussed below.
Technological Improvements in
Light-Duty and Heavy-Duty Vehicles
Efforts to improve conventional gasoline engines focus on
obtaining the optimal engine operation possible through methods
such as improving part-load operations (power required at less than
peak efficiency) and combustion characteristics, reducing engine
warm-up time, increasing compression ratios, reducing frictional
losses, and extending the operating regime of engines (Bleviss,
1988).
Another method of improving vehicle efficiency is to increase
transmission efficiency. The focus here is on reducing the losses
associated with either automatic or manual transmissions through
design changes. Automatic transmissions provide shifting at the
optimal moment (unlike manual transmissions, which depend on the
driver) so that the vehicle can remain at full load, but they have
pumping and frictional losses. Manual transmissions do not have
these losses. However, drivers do not generally operate manual
transmissions at maximum efficiency by shifting at the optimal
moment. A number of methods for increasing transmission efficiency
have
FIGURE 23.3 Fuel economy index (FEI) versus
performance index. Envelope of fuel economy and performance
measures
for a 50-car population of 1985–1986 vehicles with automatic
transmissions. Circles contain averages for the six EPA
weight
classes in 1979. Performance index is defined as the time (in
seconds) required to accelerate from 0 to 60 mph. The lower
the performance index, the better the performance.
SOURCE: Amann
(1989).
been suggested, including designs that include the continuously
variable transmission (CVT).
Reducing a vehicle's weight can yield major improvements in fuel
economy. By reducing the weight of a vehicle 10 percent, city fuel
economy can be improved 7 to 8 percent, and highway fuel economy 4
to 5 percent. The weight of the vehicle is reduced by substituting
advanced materials for the steel and cast iron that were used in
the past. New materials that can reduce vehicle weight include
high-strength low-alloy (HSLA) steel, aluminum, magnesium, and
plastics (Bleviss, 1988).
Improving the aerodynamics of a vehicle involves changing the
exterior
FIGURE 23.4 Cost of gasoline and efficiency (6
percent discount rate).
FIGURE 23.5 Cost of gasoline and efficiency (30
percent discount rate).
