Transit Bus Fuels and Air Quality
Number 5 - rev. June 2006
Public transportation agencies have taken the initiative to improve air quality by
reducing exhaust emissions from transit bus fleets. Various strategies to achieve this
goal are underway, including use of alternatives to standard diesel fuel in buses. This Resource
Guide outlines the status of alternative fuel technologies and references key
internet resources that provide background material and tools to track future
developments. It also provides representative examples of current applications of the
major bus fuel alternatives at U.S. transit agencies.
Overview
Heavy-duty diesel engines are a significant source of smog-forming nitrogen oxides
(NOx). In addition, the fine particulate matter (microscopic soot) exhaust from diesel
engines is a toxic air contaminant that has been linked to lung cancer and asthma. For
background on the health and environmental impacts of smog, check the American Lung
Association's State of the
Air 2002, the Sierra Club's Cleaning
the Air with Transit Spending, and the California
Air Resources Board web site.
Diesel fuel is used in approximately 90% of transit buses according to an APTA survey of
about 300 transit agencies. However, while the number of diesel-powered vehicles has
remained constant over the last decade, the size of the non-diesel U.S. bus fleet has
increased significantly. Four primary technologies: compressed natural gas, liquified
natural gas, hybrid diesel-electric, and fuel cells are gradually replacing standard
diesel in bus transit as the fuel of choice.
Alternative Fuels Data Center - U.S. Department of Energy
This site, provided by the U.S. DoE Office of Transportation Technology, offers a
number of resources, including a database
for heavy-duty alternative fuel bus specifications and purchase information; a glossary of key terms; and
a compilation of success
stories about alternative fuel-powered transit fleets.
Source: Alternative Fuels Data Center web site: http://www.eere.energy.gov/afdc/index.html
Guidebook for Evaluating, Selecting, and
Implementing Fuel Choices for Transit Bus Operations.
ARCADIS, Geraghty & Miller, Inc. 1998.
Provides information concerning engine and vehicle technology, vehicle performance,
fueling station design, maintenance facility modifications, safety considerations and fuel
availability and cost for: compressed natural gas (CNG), liquefied natural gas (LNG),
methanol, ethanol, and liquefied petroleum gas (LPG).
Source: TCRP Report #38. TRB web site: http://nationalacademies.org/trb/publications/tcrp/tcrp_rpt_38-a.pdf
Use of Alternative Fuels in Transit Buses.
United States General Accounting Office, December 1999.
While somewhat dated, this GAO report provides concise information on fuel
characteristics, deployment status, costs, emissions, and factors encouraging and
discouraging use for the major alternative fuels as of the end of 1999. Report is based on
interviews with 12 transit agencies using alternative fueled transit buses.
Source: US GAO Report GAO/RCED-00-18 http://www.gao.gov/new.items/rc00018.pdf
Improved Diesel Fuel
- Ultra-low sulfur diesel. Improvements can be made
to standard diesel fuel to reduce its negative impact on the environment. Ultra-low sulfur
diesel (ULSD), often referred to as "clean diesel", is being introduced into use
in transit fleets across the U.S. ULSD contains 95% less sulfur than conventional diesel,
and requires no major changes to transit operations or infrastructure. ULSD is often
coupled with advanced soot filters to further reduce emissions. The adoption of ULSD is
being driven by the 2006 US Environmental Protection Agency (EPA) standards mandating that
the sulfur content in diesel fuel be reduced from 500 to 15 parts per million. Check the
EPA web site for more specifics at: http://www.epa.gov/otaq/regs/fuels/diesel/diesel.htm
Diesel Technology Forum
This is a diesel technology industry-sponsored web site that provides technical
documents, factsheets, and latest news articles on diesel fuel and exhaust after-treatment
and focuses on "clean" diesel technologies.
Source: http://www.dieselforum.org/
The Transition to Ultra-Low-Sulfur Diesel Fuel: Effects on
Prices and Supply.
Energy Information Administration, US Department of Energy, May 2001.
This report attempts to assess whether or not there will be adequate supply of ULSD as the
new EPA standard becomes effective in June, 2006. The uncertainty of supply is addressed
both in the short-term transition period, and in the mid-term (2007-2015).
Source: Energy Information Administration http://www.eia.doe.gov/oiaf/servicerpt/ulsd/pdf/ulsd.pdf
Low-Sulphur Examples:
Greater
Cleveland Regional Transit Authority began a ULSD pilot program with 10
community circulator buses in May, 2002.
Chicago
Transit Authority slashed 195 tons of pollutants in 2003 by gassing up
its approximately 2,000 buses with ultra-low sulfur diesel.
Massachusetts Bay Transportation
Authority began powering its entire diesel bus fleet of 900+ buses with
ULSD in April, 2002.
- Biodiesel. Biodiesel is a domestically produced,
renewable fuel made from non-fossil fuel sources such as vegetable oils that can be used
in unmodified diesel engines with the current fueling infrastructure. Compared with
standard diesel fuel, pure biodiesel reduces emissions of small particles by 40 percent;
the residue is nontoxic and biodegradable. Current U.S. biodiesel production is based
largely on soybean oil and used cooking grease. Most transit agencies that employ
biodiesel use a blend of 20% biodiesel with petroleum diesel (B20) to fuel their buses.
National Biodiesel Board
This web site is sponsored by soybean manufacturing interest groups as well as other
industry and government representatives. It includes a section on transit applications of
biodiesel, numerous fact sheets, news releases and a directory of biodiesel distributors
in the U.S.
Source: http://www.biodiesel.org
Biofuels for Sustainable Transportation -
U.S. Department of Energy
Provides a wealth of background information on economic, national security, and
environmental issues relating to biofuels. Includes a separate section on biomass-derived
diesel transportation fuels.
Source: http://www.ott.doe.gov/biofuels/
Biodiesel Examples:
Bi-State
Development Agency began using biodiesel (B20) to fuel St. Louis city
buses in June, 2001.
Cincinnati
Metro announced in July 2000 that it would begin using biodiesel (B20)
fuel in its 288 city buses.
Central
Ohio Transit Authority began using in 2005 a 90 percent soy fuel 10 percent
diesel blend in all its 234 buses during warm months, reducing the percentage
to 50-50 in October and 20-80 in December.
Alternatives to Diesel
- Natural Gas. Compressed natural gas (CNG) is the
second most used power source, fueling approximately 7.5% of the transit bus fleet
nationwide. Liquified natural gas (LNG) is employed in an additional 1.5% of transit
buses. More than 70 agencies operate natural gas buses. As of January 2001, approximately
25% of all new buses on order in the U.S. are natural gas-powered.
Natural Gas Vehicle Coalition
An industry-sponsored web site that contains fact sheets, press releases and position
papers on natural gas vehicles, including transit buses. Includes NGVC's response
to the California Air Resources Board (CARB) transit bus study.
Source: http://www.ngvc.org/ngv/ngvc.nsf
Natural Gas Buses: Separating Myth from Fact.
US Department of Energy, May 2000.
This fact sheet addresses some of the most common misconceptions and misinformation
surrounding conversion to and operation of natural gas buses.
Source: US DoE, Office of Energy Efficiency & Renewable Energy http://www.nrel.gov/docs/fy00osti/28377.pdf
Natural Gas in Transit Fleets: A Review of the Transit
Experience.
Leslie Eudy, 2002.
Reports on a survey of 42 transit agencies that operate natural gas buses in their fleets,
describing their successes, difficulties, and lessons learned. Training, especially of
maintenance personnel, and adequate fueling infrastructure were among the keys to a
successful natural gas program.
Source: APTA 2002 Bus & Paratransit Conference proceedings paper. Click here for PDF file.
Natural Gas Vehicle Transit Bus Fleets: The Current
International Experience.
Glen M. Watt, 2000.
An excellent summary of the pros and cons of natural gas-powered transit buses as reported
by international transit agencies in Europe, Asia, Australia, and South America.
Source: International Association for Natural Gas Vehicles http://www.iangv.org/jaytech/files/iangv_bus_report.pdf
CNG Examples:
Los
Angeles MTA as of Spring 2006 operated the largest CNG bus fleet in North
America, with 2,200 CNG buses in operation, or 88 percent of its bus fleet.
Pierce Transit has been operating CNG
buses since 1986. At present, more than half of its 200-bus fleet is powered by CNG.
Foothill
Transit operates over one hundred CNG buses and plans an all CNG fleet
by 2010.
LNG Examples:
Phoenix PTD operates one the largest LNG bus fleet
in the U.S. with over 200 vehicles as of January 2002. An overview of its LNG program was
presented at APTA's 2000 Bus & Paratransit Conferece. Click here for PDF file.
Santa Monica's Big Blue Bus
will have 37 new LNG buses in revenue service by June, 2002.
Dallas' LNG bus fleet numbered 139 vehicles as of January 2002. A
research report on DART's LNG program published in 2000 by US DoE is available at: http://www.nrel.gov/docs/fy01osti/28739.pdf.
- Hybrid-Electric. Hybrid electric buses are
propelled by an engine powered by batteries that are in turn charged by a small internal
combustion engine. Typically, hybrid electric buses use pickup truck-sized engines and
regenerative braking to further increase fuel efficiency. Hybrid-electric buses run on a
wide variety of alternative fuels, however, diesel hybrids appeal to many transit agencies
because of the ability to utilize existing infrastructure.
Electric Drive Transportation Association
This industry-sponsored web site includes a section called "Bus Stop"
that offers bus manufacturer product information, industry news and conference
summaries.
Source: http://www.electricdrive.org/
A Review of the Performance of Hybrid-Electric Bus Technology on Fuel
Economy and Emissions. N. Clark & J. Schiavone
This paper provides a review of the present status of hybrid-electric bus
propulsion and energy storage technology. Chassis dynamometer data have confirmed
the superior fuel economy of hybrid buses.
Source: APTA 2006 Bus & Paratransit Conference proceedings paper.
Click here for pdf file.
Hybrid-Electric Transit Buses: Status, Issues, and Benefits.
Northeast Advanced Vehicle Consortium, 2000.
Addresses issues including emissions and fuel economy, technology challenges,
life cycle costs, and operation and maintenance of hybrid-electric transit
vehicles.
Source: TCRP Report #59. TRB web site: http://nationalacademies.org/trb/publications/tcrp/tcrp_rpt_59.pdf
Design Guidelines for Bus Transit Systems Using Electric and Hybrid Electric
Propulsion.
Federal Transit Adminstration, Office of Research, Demonstration and Innovation,
March, 2003.
Provides overview of hybrid-electric configurations and bus components, addresses
safety issues in vehicle operations and maintenance/storage facilities, and
outlines personnel training needs for operators and mechanics.
Source: FTA web site:
http://transit-safety.volpe.dot.gov/Publications/cleanair/DesignGuidelines/HTML/DesignGuidelines.htm
Hybrid Examples:
New
York City Transit marked the completion of its first order of 325 diesel
hybrid-electric buses in early 2006, with an additional 500 scheduled to enter
service by the middle of 2007. A final report (July 2002) on NYCT's hybrid-electric
pilot program involving 10 prototype buses in revenue service is available
at: http://www.ctts.nrel.gov/heavy_vehicle/pdfs/nyct_final_results.pdf
Roaring Fork Transportation Authority put the first four of seven
hybrid-electric buses into service in Aspen Colorado. The New Flyer Transit
buses are powered by General
Motors hybrid technology. The buses will operate under unique conditions
included elevations above 9,000 feet, climbing grades as steep as 12 percent.
Oahu Transit
began operating 75-passenger hybrid buses with frequent service and specially
designed shelters and stations in November 2004.
King
County Metro has ordered 213 hybrid diesel-electric 60-foot articulated
buses plus another 22 hybrids for Sound Transit. The first hybrids began operation
in May 2004 and are expected to save 750,000 gallons of fuel a year.
- Fuel Cells. In public transportation, fuel cells
are in the evaluation and testing stages by both manufacturers and transit properties,
with a number of pilot projects underway or recently completed. Some transit professionals
view fuel cell buses as the "long-term future of low-emission vehicles". Fuel
cell engines can run on a potentially unlimited renewable source of fuel - hydrogen gas.
The cells produce electricity by directly mixing hydrogen stored as fuel and oxygen taken
from the air without combustion. The only emissions created by fuel cells are
non-polluting water and carbon dioxide. While a relatively new technology, fuel cell power
is attractive in that it provides the potential for dramatically reducing air pollution,
greenhouse gas emissions, and petroleum-based energy use.
National Hydrogen Association
This industry-sponsored web site offers a primer on hydrogen as a fuel source and
addresses issues relating to infrastructure, standards and safety.
Source: http://www.hydrogenus.com/
Fuel Cells 2000
Sponsored by the Breakthrough Technologies Institute, this site includes a
non-technical presentation of how fuel cells work, a monthly news update on fuel cells,
and a separate section on application of fuel cells to mass transit.
Source: http://www.fuelcells.org/
Georgetown University Advanced Vehicle Development
The Fuel Cell Bus Program at Georgetown University is funded by grants from the
Federal Transit Administration to support the development of fuel cell technology for
transit applications.
Source: http://fuelcellbus.georgetown.edu/index.cfm
Fuel Cell Examples:
AC Transit and SunLine Transit Agency announced
in June, 2002 that they were jointly purchasing a total of four hydrogen fuel
cell buses. These vehicles will be the first fuel cell buses to be placed
in regular service in the U.S. An audio presentation "Hydrogen Bus Service
in Oakland, California" (June 2001), describing an earlier fuel cell
bus pilot program at AC Transit, is available at: http://www.ch2bc.org/
.
Lynx in Orlando, Florida, along with the Orlando International Airport and
Orange County is entering into a demonstration project to add four hydrogen-fueled
nine-passenger vans to their mostly diesel-powered fleet
beginning in mid-2006. The hydrogen-powered engine provides near-zero regulated
and carbon dioxide emissions.
Source: Orlando Business Journal, March, 27, 2006 Read
article
Santa Clara
Valley Transportation Authority (VTA) began operating three hydrogen fuel
cell-powered zero emission 40-foot buses (ZEBs) in regular service in Spring
2005.
APTA Information Center
info@apta.com
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