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THE NATIONAL CLEAN BUS
NETWORK
Clean Bus Fact
Sheet
The
Status of Bus Transportation
Buses
are a vital part of our nation’s public transportation system. A
significant number of adults and children rely on bus transportation
to get to important destinations such as work and school. In fact,
in 2001, transit buses carried three-fifths of public transit riders
and transported 25 million children to school,
making buses by far the most important and most common mode of mass
transit service in the
United
States
.
Importantly, statistics show that demand for public transportation
has been growing steadily. In the past six years transit ridership
increased 24 percent, even greater than highway or air travel.
Increasingly, transit planners are turning to buses and bus
technologies (e.g., bus rapid transit) as cost-effective mass
transportation options.
Yet,
the overriding majority of our nation’s bus fleet relies on
conventional diesel engines,
which negatively impact public health, the environment, and national
energy security. In a survey of major transit agencies, the American
Public Transportation Association (APTA) estimates that 76,075
transit buses were in active service nationwide during fiscal year
2001.
About 11.6 percent of transit buses represented in the APTA survey
were powered by an alternative source, up from 4 percent in 1996.
Transit buses consumed 587 million gallons of diesel in 2001, not
including the volume of diesel and gasoline consumed by the
nation’s school buses. The national school bus fleet, totaling
454,000 vehicles, is similarly dependent on petroleum fuels. The
Union of Concerned Scientists estimates that 86 percent of school
buses use diesel, while an additional 13 percent continue to use
gasoline, leaving one percent which fuel with an alternative like
natural gas, biodiesel or propane. Nearly half of school buses
powered by alternative fuels use propane, but this number will
decrease as school districts face a decreasing supply of propane bus
manufacturers.
Northside
Independent
School
District
,
a propane bus user since 1981, is faced in 2003 with its first
purchase of diesel-powered buses in 22 years. Due to low demand,
manufacturers of the propane bus chassis have elected to take it out
of production. Against its wishes, the school district is being
forced to transition to a petroleum-powered bus fleet.
In
January 2001, the U.S. Environmental Protection Agency (EPA)
promulgated new heavy-duty engine and vehicle standards to reduce
emissions of particulate matter and nitrogen oxides from buses.
These regulations include a requirement on diesel fuel refiners to
produce diesel fuel with lower sulfur content (15 parts per million)
by mid-2006. New emissions standards for heavy-duty engines will
take effect in model year 2007. In the interim, the EPA is
encouraging the use of low-sulfur diesel in combination with new
emissions control technologies. This gradual transition to
low-sulfur diesel will prevent some of the problems associated with
conventional diesel fuels. However, low-sulfur or “clean” diesel
will continue to emit both air toxins and ultra fine particulate
matter, which studies show may cause cancer and other forms of lung
damage. Additionally, low-sulfur diesel does not reduce emissions of
carbon dioxide, the primary greenhouse gas, nor reduce dependence on
petroleum fuel. There are other alternatives to low sulfur diesel
capable of resolving to a greater extent a number of these issues.
Moreover, the use of advanced technologies in public transportation
provide valuable on the ground experience for such products that
will assist our transition to superior propulsion and energy storage
systems, such as renewable hydrogen fuel cell technologies.
Problems
with Petroleum Diesel
Greater
risk of cancer
The
National Institute of Occupational Safety and Health, the
International Agency for Research on Cancer, the US EPA and the
California EPA have agreed that a relationship exists between diesel
exhaust exposure and lung cancer. The South Coast Air Quality
Management District (SCAQMD) has found that particulate emissions
from conventional diesel are responsible for 71 percent of airborne
cancer risk.
A report by the administrators and officials responsible for state
and local air pollution control estimates that in the
United
States
,
diesel could be responsible for over 125,000 additional cancers over
a lifetime of exposure
Linked
to asthma and other respiratory diseases
The
EPA has shown that fine particulate matter and oxides of nitrogen
within diesel exhaust can impair lung function, contribute to
asthma, decrease the body’s respiratory defense mechanisms, and
lead to acute respiratory illness. Ninety-eight percent of diesel
emissions are composed of fine particulates capable of lodging deep
into the lungs and inflicting respiratory damage. Poor community
health as a result of particulate pollution has been linked to
greater numbers of hospital stays for respiratory disease, pulmonary
diseases, pneumonia, heart disease and death. In 2000 the EPA
indicates that diesel vehicles like trucks and buses were
significant contributors among highway vehicles of nitrogen oxide
and fine particulate matter. While they produced 40.5 percent of
highway vehicle emissions of nitrogen oxide, they emitted 69.4
percent of highway emissions of fine particulate matter. According
to the new American Lung Association report, over 137 million
Americans are exposed to unhealthy levels of ozone. Control of
nitrogen oxide emissions is important since these are precursors to
ozone formation.
Greater
health risks to children
Children
are among the most susceptible to the health effects of diesel
exhaust exposure because of their higher breathing rates; greater
time spent outdoors, and increased level of activity.
The Union of Concerned Scientists has shown that children
riding a school bus are exposed to diesel exhaust concentrations
four times higher than if they were walking or riding beside it. A
study led by the
University
of
Southern
California
has shown that the inhalation of nitrogen oxides, a significant
component of diesel exhaust, is related to decreased lung function
growth in children.
Threats
to the Natural Environment
Incomplete
combustion of petroleum diesel produces exhaust laden with
particulates and chemical compounds, contributing to regional haze,
acid rain and global warming. The
U.S.
transportation sector emits approximately one-third of all
U.S.
heat trapping gases. A 2001 study published in the journal Nature
estimates that black carbon soot like that from diesel exhaust could
be responsible for 15 to 30 percent of global warming.
Geopolitical
Vulnerability
The
U.S.
transportation sector relies almost entirely on petroleum fuel.
Nearly 98 percent of all transit operations use petroleum, while
imports satisfied 54 percent of net petroleum consumption in 2001.
The Energy Information Administration (EIA) in its 2003 Energy
Outlook projects net petroleum imports to account for 68 percent of
U.S.
demand in 2025
Environmental
Injustice
Pollution
from diesel buses impacts a disproportionate number of low-income
communities. Citizens in these communities rely upon diesel-powered
buses to commute to school and to work. They are exposed more
frequently and more directly to harmful diesel emissions both
through travel and through proximity to bus refueling and
maintenance stations.
Clean
Bus Technologies and Status
Natural
Gas Technologies
Natural
gas is a fossil fuel composed of methane, ethane and other
hydrocarbons drawn from gas or crude oil wells. It is stored in
compressed (CNG) or liquefied (LNG) form in high pressure cylinders
and more commonly fed into spark-ignited engines. However, newer
heavy-duty natural gas-powered engines without spark ignition have
become available. Currently one out of every five alternatively
fueled transit buses is powered by natural gas. In 2001, CNG buses
accounted for one-fifth of all new bus orders
Natural
gas engines produce substantially fewer emissions of particulate
matter, carbon monoxide and nitrogen oxides than conventional diesel
engines. Many natural gas engines already meet or exceed the 2004
EPA heavy-duty engine emission standards.
TABLE
1: Natural Gas Emissions Compared to Conventional Diesel
|
Carbon Monoxide
|
90%
to 97% reduction
|
|
Carbon Dioxide
|
25% reduction
|
|
Nitrogen Oxides
|
30% to 60%
reduction
|
|
Particulate Matter
|
90% reduction
|
|
Non-methane
hydrocarbons
|
50% or greater
reduction
|
|
Fuel Economy
|
15% to 20%
reduction
|
In
the year 2000, domestic production accounted for 84 percent of
total natural gas consumption. Canadian imports account for the
majority of the remaining 16% of natural gas consumed in the
US
.
Costs
of bus fleet conversions to natural gas technologies are
concentrated in the initial capital investment. The purchase cost
of a CNG bus can range from $25,000 to $50,000 more than a diesel
bus. This price differential is expected to grow narrower as
production volumes of CNG buses increase. Also, investment in
natural gas fueling infrastructure usually requires construction
of a new fueling facility. These fueling facilities can be an
investment in future natural gas vehicle fleets that will demand
public refueling stations. The Federal Transit Administration has
estimated the cost of a fueling station for a fleet of 200 buses
at approximately $1.7 million. Finally, National Fire Protection
Association (NFPA) codes may require modification of bus storage
depots to incorporate gaseous fuel detection systems. Despite
these added costs, operational and maintenance expenses tend to be
lower than those for diesel-powered buses, including newer
”clean diesel” models fitted with after-treatment devices.
Natural gas-powered buses save money because they do not require
frequent oil changes and regular cleaning and eventual replacement
of new filters. Since natural gas engines are inherently cleaner
burning and experience less engine wear, normal maintenance costs
tend to remain low, but these costs have varied among transit
agencies.
In
1993, the Los Angeles Metropolitan Transit Authority committed to
purchasing only alternative fuel buses. It currently operates over
1,900 dedicated CNG buses, the nation’s largest fleet. The
Metropolitan Atlanta Regional Transit Authority and New York MTA
Long Island Bus Co. have also committed to alternative fuel-only
purchases and operate substantial numbers of CNG buses. SunLine
Transit Agency in Thousand Palms, CA became the nation’s first
100 percent CNG bus fleet in 1994 while Pierce Transit Agency in
Tacoma
,
Washington
was one of the first to use a natural gas-powered heavy-duty
engine.
LNG
buses are less common than CNG, although market share for LNG
buses is growing rapidly. The slower market penetration is due in
part to the current limitations in LNG fueling supply and
distribution network. One advantage is that fuel density of LNG is
higher than CNG, which means that the same BTU content (and thus,
vehicle range) weighs less and may be stored in less space,
typically a single cryogenic liquid tank rather than the multiple
gaseous fuel storage cylinders associated with CNG units.
Emissions performance is about the same as CNG because they both
start as natural gas although the methane content of LNG is
usually slightly higher than CNG originating from pipeline gas.
Transit agencies in
Orange County
,
CA
;
Dallas
,
TX
; and
Phoenix
,
AZ
operate some of the nation’s largest LNG bus fleets.
Biodiesel Technology
Biodiesel,
a renewable fuel derived from animal fats and vegetable oils, is a
diesel fuel substitute that can be used in heavy-duty diesel
vehicles like trucks and buses with no engine modification. The
main feedstock for biodiesel can be domestically produced from
agricultural commodities like soybeans and rapeseed, or refined
from used frying oil and unwanted animal fats. Currently it is
more commonly found mixed at a ratio of 20 percent biodiesel to 80
percent diesel, otherwise referred to as B20.
Table
2: Emissions from B20 Compared to Conventional Diesel
|
Hydrocarbons
|
20% reduction
|
|
Carbon Monoxide
|
12% reduction
|
|
Carbon Dioxide
|
16% reduction
over lifecycle
|
|
Nitrogen Oxides
|
2% Increase
|
|
Particulate
Matter
|
12% Reduction
|
|
PAH & nPAH
compounds
|
16% to 18%
reduction
|
|
Fuel Economy
|
2% reduction
|
The costs
associated with converting to biodiesel are relatively low.
Diesel fuel storage tanks already in place can just as easily
store biodiesel. Greater costs can be incurred when a fuel
mixture containing a high ratio of biodiesel is used.
Pure Biodiesel has a tendency to act as a solvent, releasing
fuel tank deposits accumulated under conventional diesel use.
Costs are incurred when these deposits clog engine filters
(filter clogging occurs in less than 3% of vehicles). The
filters must be replaced periodically until all significant
deposits have been removed.
Compared to petroleum diesel, B20 increases
nitrogen oxide emissions of 2 percent. This may raise concerns
for local decision makers working to decrease concentrations of
ozone in their area. Research is currently underway to develop
technical fixes to reduce nitrogen oxide emissions from
biodiesel, like an additive to make it burn cleaner or a
nitrogen oxide capture device that could be fitted on the
tailpipe of the vehicle. In
the meantime, this emissions characteristic poses a significant
challenge to wide-scale adoption in ozone non-attainment areas.
In
October 2002 the Clark County School District serving Las
Vegas, Nevada and surrounding areas became the largest biodiesel
fleet in the world with over 1000 vehicles. The primary source
of the fuel is used frying oil taken from Las Vegas
Casinos and hotels. The Medford Township school district in New
Jersey began using biodiesel in 1997 and has done so longer than
any other fleet in the United States.
Hybrid
Propulsion Technology
Several
hybrid systems have been developed for use in bus transit
applications. Hybrid propulsion systems integrate a combustion
engine with one or several electric motors and can take two
forms: series or parallel. A series hybrid bus is currently
being demonstrated in
Chattanooga
,
Tennessee
, using a turbine engine to drive electric motors
at the wheels and charge the on-board battery.
The turbine engine is powered by jet fuel to keep
emissions low, but any fuel like biodiesel, propane or natural
gas could be used in combination with a hybrid propulsion system
optimized for the chosen fuel. A parallel hybrid system allows
electric and mechanical propulsion to work side-by-side. At high
speeds the combustion engine drives the wheels and charges the
battery, but at low speeds when the engine operates less
efficiently, the on-board battery takes over and propels the
vehicle. On-board batteries take advantage of regenerative
braking technology, using generators in the wheels to convert
forward energy into electricity to charge the batteries when
braking, thereby conserving fuel. By increasing engine
efficiency, hybrid systems produce fewer emissions per vehicle
mile traveled.
Table
3: Emissions of a Diesel Hybrid-Electric Propulsion System
Compared to Conventional Diesel
|
Hydrocarbons
|
28% reduction
|
|
Carbon Monoxide
|
98% reduction
|
|
Carbon Dioxide
|
33% reduction
|
|
Nitrogen Oxides
|
44% reduction
|
|
Particulate
Matter
|
99% reduction
|
|
Fuel Economy
|
16% increase
|
New
York City Transit tested a total of 10 hybrid-electric buses from 1998 to 2002 and will receive 125 more during the fall of 2003. By
2006, a total of 335 buses will be in operation by the fleet.
Dana Lowell, assistant chief maintenance officer of MTA New
York City Transit, describes their experience with hybrid vehicles as “very positive – for a brand new technology,
[hybrid buses] have exceeded expectations”. These vehicles
have achieved a 16 percent improvement in fuel economy over
standard diesel buses, while requiring little to no
investment in training or infrastructure.
Hydrogen
fuel cells combine on-board hydrogen with oxygen in the air to
generate electricity and water vapor. Fuel cells are about 40
to 60 percent efficient in converting energy, compared to
about 20 percent efficiency for internal combustion engines.
Fuel cells produce no harmful emissions, potentially
eliminating vehicles as sources of air pollution.
Fuel
cell technology for transit buses has been in the research,
development, and demonstration stage for several years. In
1994,
Georgetown
University
began one of the first fuel cell bus
demonstrations using methanol. Since the late 1990s, the
number of demonstrations increased dramatically. Today,
practically every bus manufacturer in
North America
and
Europe
is involved in some form of fuel cell bus
demonstration activity. The European Fuel Cell Bus Project
will operate 30 fuel cell buses in ten cities to demonstrate
and test the technology beginning in 2003. The California Fuel
Cell Partnership in 2002 already began operation of the
world’s first fuel cell bus in revenue service in Thousand
Palms, CA.
Despite its benefits, there are serious concerns that
fuel cells may continue demand for polluting sources of
energy. While the fuel cell itself may be clean, hydrogen
pollution can become a major new pollution source. Though
hydrogen is the most abundant element in the universe, it is
not easily found in its pure form. Rather, it is bound up in
combination with other molecules and must be separated from
them. The water molecule provides one of the most abundant and
accessible sources of hydrogen. However, the process of
electrolysis, the separation of water into hydrogen and
oxygen, requires electricity. The source of this electricity
can come from any energy source, including nuclear, coal and
others that pollute the air and water. Hydrogen is also
abundantly found in hydrocarbon fuels, including natural gas
and other petroleum products. However, the process of
generating hydrogen from these products also produces unwanted
emissions. The only known way to keep hydrogen fuel cells as
truly renewable, non-polluting sources of energy is to ensure
that hydrogen is generated through renewable means using
solar, wind, geothermal, biomass and hydroelectric energy to
drive electrolysis, or through controlled biological processes
using enzymes and algae, for example.
Table
4: Emissions of a Hydrogen Fuel Cell Compared to Conventional
Diesel
|
Hydrocarbons
|
100% reduction
|
|
Carbon Monoxide
|
100% reduction
|
|
Carbon Dioxide
|
100% reduction
|
|
Nitrogen Oxides
|
100% reduction
|
|
Particulate
Matter
|
100% reduction
|
The
federal research initiative proposed by President George W.
Bush in his 2003 State of the Union speech may speed up the
timeframe to fuel cell commercialization. Among the hurdles
still to be resolved are the construction of a cheap and
reliable hydrogen distribution system as well as a reduction
in the weight and cost of current prototype fuel cells.
SunLine Transit Agency of Thousand Oaks, CA in
October 2002 began the first operation ever of a fuel cell
bus in revenue service; while in
Europe
, Daimler Chrysler has planned a two-year demonstration of 30 Citaro
fuel cell buses in ten cities. Explaining Daimler
Chrysler’s plan, Dr. Eckhard Cordes, head of commercial
vehicle busines stated, “Urban bus transport is the ideal
field for practically testing the fuel cell as a vehicle
propulsion system.” Buses are part of a “niche” market
where technical and other resources are centralized, making
fueling, maintenance and problem-solving easier.
Policy
Options
The
federal transportation bills – the Intermodal Surface
Transportation and Efficiency Act of 1991 (ISTEA) and the
Transportation Equity Act for the 21st Century
(TEA-21) – provided an excellent foundation for the
conversion to cleaner vehicles.
The reauthorization of TEA-21 presents an important
opportunity to build on this promise and deliver a full
range of modern, safe and cost-effective transportation
options that meet the expectations and needs of
U.S.
citizens. Upcoming TEA-21 reauthorization
provides two important opportunities. The Congestion
Mitigation and Air Quality Improvement Program (CMAQ) is
potentially the largest federal source of funding for
purchase of vehicles powered by alternative fuels and
technologies and related infrastructure. The Clean Fuels
Formula Grant Program established by TEA-21 can also provide
the greatest federal assistance directed specifically to the
deployment of clean buses and support mechanisms. In
addition to these, other policy options have become
available. The Energy Policy Act of 2003 currently being
considered in Congress, is another opportunity for
supporting the use of energy-efficient, advanced vehicle
technologies, while incentives such as those proposed by the
Clean Efficient Automobiles Resulting from Advanced Car
Technologies (CLEAR) Act of 2003 would provide tax credits
for the purchase of light and heavy duty vehicles, the
construction of alternative fueling infrastructure, and the
purchase of alternative fuels. These and other legislative
opportunities represent important policies through which the
federal government can take action to support the deployment
of cleaner buses.
Clean
Fuels Formula "Clean Bus" Grant Program (49 USC
5308)
Federal
funding for the Clean Fuels Formula “Clean Bus” Grant
Program to assist local clean bus efforts was authorized in
the Transportation Equity Act of the 21st Century
(TEA-21), but this program was never implemented as
intended. TEA-21 authorized a minimum of $100 million per
year beginning in fiscal year 1999 and ending in fiscal year
2003 for the purchase of clean fuel buses, construction,
modification and/or leasing of associated facilities, and
repowering or retrofitting of existing buses. However, this
source of funding was never appropriated in accordance with
TEA-21 authorizing legislation; instead these funds were
largely earmarked for specific projects. Additionally, the
Department of Transportation delayed several years in
writing regulations for the program. These are necessary to
explain application procedures to applicants seeking clean
bus funding and make clear other information not already
provided in public law. Final rules for the Clean Bus
Program were finally published in the Federal Register
June 11, 2002
, a delay which unfortunately prevented the use
of guaranteed funds for fiscal years 1999 through 2002.
Again in fiscal year 2003, congressional appropriators
diverted clean bus funding from its intended purpose,
despite the newly published program rules.
The
Clean Bus Program could be reinvigorated to encourage
greater deployment of clean buses to assist local areas in
meeting air quality standards, reduce dependence on imported
oil and help pave the way for wide scale commercialization
of advanced vehicle technologies. Buses serve as excellent
test vehicles for deployment of new technologies because
they are centrally fueled and maintained by professionals.
For example, a revamped Clean Bus Program could cover the
differential cost of cleaner buses over that of comparable
conventional buses, and provide funding, at an 80 percent
cost- match, of clean fuels infrastructure to support this
deployment. Rebate
programs would also help local communities to absorb clean
bus costs that provide national benefits.
Congestion
Mitigation and Air Quality Improvement Program
The
U.S. Department of Transportation’s Congestion Mitigation
and Air Quality (CMAQ) Improvement Program, an important
component of TEA-21, has provided a substantial amount of
money for transit but extremely little for alternative fuels
and advanced vehicle technologies. At a May 2002 EESI
briefing, Ken House, Democratic Staff Director of the House
Transportation and Infrastructure Committee,
described this as a serious shortcoming in the original
intent of the program, intended not only to improve air
quality but also to “support the emerging
technologies.”
Expansion
of CMAQ funds to include all pollutants regulated under the
Clean Air Act (including PM 2.5), as well as greenhouse has
emissions and increases of CMAQ funds proportional to the
population of all newly designated non-attainment areas
(once new air quality rules are implemented) is an important
issue to be considered.
A greater allocation of funds to local and regional
levels could provide creativity and responsiveness in
meeting local transportation and air quality improvement
needs. Allocating
funds based on established goals and performance standards
and implementing an evaluation program to assess performance
could also help ensure positive results.
In general, air quality improvement and public health
protection need to be central to the distribution of such
funds.
Future
Outlook
Fuel
cell technologies have demonstrated the greatest potential
for eliminating the health risk of bus transit emissions and
dependence on foreign petroleum supplies, but these
technologies are not yet ready for commercial production,
nor does the requisite fueling infrastructure exist. During
the ten to fifteen years projected as necessary for fuel
cell technologies to reach maturity, short and medium term
technologies are available at realistic prices with proven
benefits. Of these, hybrid technologies, after-treatment
devices and natural gas technologies significantly reduce
emissions of air toxins and criteria pollutants. Natural gas
engines are proven in the field and have already been widely
adopted, while hybrid engines though still in the
demonstration stage, have shown great promise. Low sulfur
diesel and after-treatment devices through government
regulation will become standard in 2007. Biodiesel presents
important opportunities for immediate adoption of a
domestically produced, renewable fuel without the need for
high capital investment in new engines. It can also be used
in conjunction with hybrid engines, low-sulfur diesel and
after-treatment devices to further reduce emissions. Each of
the above technologies satisfies different demands and will
be adopted in the future by customers capable of absorbing
their associated costs.
Clean
buses are an important part of our transportation future as
consumer demand and government support for buses, cleaner
fuels and advanced vehicle technologies grows. Technologies
are available today to resolve the problems of petroleum
diesel, but their integration into this nation’s
transportation sector has yet to receive the full government
and public support it needs to grow. This will ultimately
determine the future of clean bus transit.
For
more information, contact Ray Minjares at 202-662-1883 or by
email at rminjares@eesi.org.
The price of biodiesel has
historically been higher than petroleum diesel, but this
price is likely to decrease as production and distribution
capacity improves. Current domestic production capacity of
biodiesel stands at around 15-20 million gallons a year and
is expected to grow. According to the nation’s clean
cities coordinators (www.ccities.doe.gov), the average price
of B20 varied between $1.46 and $1.73 in October and
November of 2002.
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