Environmental Issues > Energy Main Page > All Energy Documents

Top of Report

Chapter 6


While NRDC and the Coalition are not advocating any particular alternative fuel -- we are advocating that public and private fleets reduce their use of diesel to help clean up our air. In addition to providing environmental benefits, switching to cleaner alternative fuels will also help reduce our nation's overwhelming reliance on imported petroleum. No diesel engine on the market can match the emissions reductions of the cleaner alternative fuels in real world conditions. Recent government-sponsored emissions tests of the newest, cleanest diesels have been unimpressive. Natural gas and stored electric power are currently the leading alternative fuel technologies for transit and school buses whereas natural gas technology has been used for most other heavy duty applications.

Natural gas appears to be the best option for heavy-duty applications due to the technology's wide range in horsepower ratings, moderate initial costs when compared with electric options, potential savings in maintenance and operating costs over diesel counterparts, as well as substantial emissions reductions. Based on the emissions calculations in Table 3, the lifetime emissions benefits of operating a compressed natural gas (CNG) transit bus instead of a new diesel transit bus is equal to 15,900 pounds of NOx, 130 pounds of PM, and 370 pounds of Hydrocarbons (HC). Carbon monoxide emissions from a CNG bus, however, are 11,500 pounds greater when compared to the diesel engine*, but well below the 2004 federal and California State standards.113 In fact, the CNG engine meets all of the federal and California State standards for the year 2004, whereas diesel engines only meet 1998 federal and California State standards. The NOx emissions savings from a bus using CNG rather than diesel would be equivalent to removing 55 passenger cars from the road; PM savings would be equivalent to removing 17 cars from the road.** Further, today's natural gas buses are compatible with future hybrid buses, and could be a bridge to the longer-term solution of fuel cell powered buses that run on a renewable hydrogen energy source.

Table 3. Emissions Comparison of Diesel and CNG Buses

  Dieselc CNGd Dieselc CNGd




















GHG (CO2-eq)g    



   a. Certified emissions data from CARB's 1998 Model Year Heavy-Duty On-Road Certification Listing. Values are expressed in grams per brake-horsepower-hour (g/bhp-hr), a measure of the mass emissions released per unit energy consumed by the engine.
   b. Calculated from certified emissions data using CARB conversion factors of 4.3 bhp-hr/mi for diesel engines and 4.1 bhp-hr/mi for CNG (CARB 1996). Data from the US Environmental Protection Agency suggests that applying the same conversion factor for all pollutants is inappropriate and has identified empirically-derived estimates that would widen the gap between CNG and diesel for particulate emissions (U.S. EPA 1992).
   c. Data for a 330 horsepower Cummins M11-330E diesel engine.
   d. Data for a 300 horsepower Cummins L10-300G CNG engine.
   e. Engine certification data for the Cummins C series engine (which has a 15% smaller engine displacement) indicates CO emissions are 0.11 g/bhp-hr, or less than the diesel engine, due to improved oil control compared to the L10 engine shown in the table.
   f. Cummins L10-300G certifies at 4.1 g/bhp-hr which is the value at the end of its useful life (i.e., 290,000mi). The end of life value includes the deterioration factor of 8.54 which means a new engine only emits 0.48 g/bhp-hr. Thus the average emissions value over the engines useful life is 2.3 g/bhp-hr since a typical urban transit bus is rebuilt at the end of its useful life.
   g. Greenhouse gas (GHG) emissions over the entire fuel cycle (fuel production, transmission, and end-use), expressed as carbon-equivalents based on the relative radiative forcing (global warming potential) of key GHGs. Assumes 23.9 MMTC-eq/Quad for diesel fuel and 18.3 MMTC-eq/Quad of CNG (Delucchi 1995) and a fuel economy of 3.3 mpg for an average diesel bus and 2.7 mpg (diesel equivalent) for a CNG bus (CARB 1996). End-use emissions, including both carbon dioxide and methane, are from CARB (1996).

Hybrid-electric technology applications combine an internal combustion engine with electric battery power, resulting in a bus that has the potential to reduce emissions and increase fuel economy. While this technology shows promise in certain vehicle niches, it is still too soon to judge this technology in the transit bus world, and full-scale commercialization remains years away. Also, the environmental benefits will ultimately depend on the fuel and technology of the internal combustion engine. As Table 4 demonstrates, a diesel hybrid bus emits 60 percent more NOx and eighty percent more particulates than a dedicated CNG bus, putting aside the issue of toxicity. Clearly, a hybrid-electric bus that relies on a CNG engine will be far cleaner than one that relies on a diesel engine.

Table 4. Test Results for a Diesel Hybrid Prototype v. Dedicated CNG




Nitrogen Oxides (g/mi)



Particulates (g/mi)



   h. Mark, Jason, et al. Shifting Gears: Advanced Technologies and Cleaner Fuels for Transit Buses. Union of Concerned Scientists. April 1998. p. 25.

While battery-powered electric buses offer the greatest air quality benefits at the tailpipe, it seems they are best suited for light- or medium-duty vehicles such as shuttle vans. Electric buses are expensive, have associated power plant emissions, and their limited battery life means limited operating range. But battery technology is advancing rapidly and this technology is likely to play a significant role in the future of transportation. Furthermore, internal combustion engines deteriorate over time causing their emissions to increase, whereas electric vehicles do not experience any deterioration in emissions and in fact become cleaner over time as power plant emissions are reduced.

Fuel cell technologies for transit bus applications are also developing rapidly and may be a major energy source for heavy duty vehicles in the near future. Fuel cells, which are powered by air and hydrogen, would transform heavy duty vehicles to true zero emission vehicles. With its high efficiency and extremely low (and potentially zero) emissions, fuel cells offer enormous promise for use in vehicles, especially for buses and freight trucks. Fuel cell vehicles can rely on either hydrogen canisters or an on-board gas generation system (called a "reformer") which produces hydrogen from CNG or another fuel. In either case the fuel cell operation produces only heat and pure water as by-products, but reformers do produce small emissions levels. In noise levels, too, the fuel cell is superior: fuel cells operate silently. Far greater efficiency can be achieved with a fuel cell than an internal combustion engine. Fuel cells are being developed for transit bus use, and three prototypes are currently being demonstrated by the Chicago Transit Authority.114

Although each of these alternatives deliver significantly lower emissions than the latest model diesel engines, these cleaner alternatives have been hampered by limited engine production, higher initial costs, a limited refueling infrastructure. Inconsistent public policy signals, in the form of either regulatory requirements or incentives, have also delayed the commercialization of these cleaner technologies. The interest level as well as the success of the alternative technologies has varied depending on the application and commitment of the operator but there have been wonderful successes. Many transit and school bus operators across the country are experiencing both lower emissions and lower operating costs with natural gas buses. In several regions of the country, transit operators are receiving high praise from the public for the use of quiet, zero-emission, battery-powered electric shuttle buses. And increasingly, heavy-duty truck owners are realizing the benefits of operating alternative fuel vehicles. In the remainder of this chapter, we highlight just a few of the success stories experienced by public and private heavy-duty fleet operations.

Focus #6: Using Incentives to Spur Cleaner Fuels

Many diesel operators are ready to make the move to alternative fuels but lack the funds to cover the incremental cost of alternative fueled vehicles and equipment. Incentive programs, including direct grants or tax credits, can play a significant role by helping to cover a portion of the incremental cost associated with purchasing cleaner vehicles and establishing the necessary fueling infrastructure.

In California, Assembly Member Antonio Villaraigosa and Senator Jim Brulte have introduced legislation to appropriate $50 million: 1) to assist operators of heavy-duty diesel vehicles and equipment to purchase new low-emission vehicles and technologies; 2) to help operators clean-up diesel vehicles and equipment already in use; and 3) to fund the development of a refueling infrastructure to support these cleaner alternative fueled vehicles and equipment.115

Separately, the Planning and Conservation League, Natural Resources Defense Council, and Union of Concerned Scientists are proposing a ballot initiative which would distribute some $200 million in tax credits per year for the next 12 years. The tax credits would be available to individuals, businesses and agencies to offset the incremental cost of purchasing new or retrofitting existing vehicles and equipment to achieve emission levels significantly below the levels required by regulation.

While not a replacement for strong regulatory action, incentive programs are an essential element of an expedited transition to cleaner, safer alternative fuel vehicles and equipment.

Alternative-Fuel Heavy-Duty Trucks Make a Strong Showing

In the last few years, an increasing number of companies have started to manufacture natural gas engines with a wide variety of engine models. Heavy-duty truck operators have also shown an increased interest in alternatives to diesel. This change has resulted from a variety of factors, including the improved availability of alternative-fuel engines and trucks, less expensive fuel, lower maintenance costs, and lower emissions. Lower emissions are attractive to operators because they often can improve employee relations and the company's public image.

Currently, natural gas engines are available from most of the major heavy-duty engine manufacturers including: Caterpillar, Cummins, Deere, Mack, and Detroit Diesel. Similarly, natural gas-powered heavy-duty trucks are available from some of the leading truck manufacturers such as Freightliner, Kenworth, Peterbilt and Volvo.116 Another option is to convert diesel engines to run on a combination of alternative fuels and diesel with a retrofit kit. Power Systems Associates located in Whittier, California, is currently selling a dual-fuel retrofit package, which can be used on Caterpillar heavy-duty engines. The completed conversion is a dual-fuel power train optimized to run simultaneously on both liquefied natural gas and a small percentage of diesel, but can "limp home" solely on diesel if necessary.117

Clean Truck Success Stories

Raley's Groceries, Sacramento California

Raley's operates a chain of 87 supermarkets in northern California and northwest Nevada. In April 1997, Raley's purchased eight LNG trucks manufactured by Kenworth. The eight LNG trucks make up about 20% of Raley's total fleet. Each truck operates 16 hours per day, 5 or 6 days per week, with a range of up to 600 miles per fueling.118 Operating the LNG trucks will reduce Raley's consumption of diesel fuel by approximately 100,000 gallons per year.119 The Sacramento Metropolitan Air Quality Management District (SMAQMD) estimates that each Raley's LNG engine will produce approximately 60% less pollution than a typical diesel engine. This will result in a NOx reduction up to 40 tons during the first seven years of operation. The SMAQMD provided $600,000 to fund the construction of the fueling station for Raley's and to help offset the higher cost of the trucks.

An August 1997 article in Fleet Equipment Magazine reported that the drivers who operate the LNG trucks seem satisfied with the rigs. Raley's LNG trucks are painted blue with white puffy clouds. "The intent of the blue trucks was to catch people's eye and let them know we're trying to improve the air quality," said Andreotti, Raley's transportation supervisor. "So far we're accomplishing that."120

HEB Grocery Company, Houston Texas121

HEB Grocery Company, which operates over 250 Class 8 heavy-duty trucks at three distribution centers in Texas, has been using LNG trucks in their fleet since January 1998. Specifically, the company operates ten LNG trucks at their Houston depot with the Caterpillar dual-fuel C-10 engine.*** While HEB encountered some initial difficulties with venting of LNG on their trucks,**** they are making significant progress with this issue. Seven of the trucks are now operating with no difficulties, while three of the vehicles are still venting some fuel. All ten vehicles are operating along normal HEB routes.

Once HEB has had the opportunity to evaluate the in-use performance of these vehicles for a sufficient time, the company intends to convert their entire Houston fleet of 54 trucks to LNG. Company officials have indicated their desire to purchase the additional 44 tractors by the end of 1998. HEB has proceeded with their LNG efforts with no public support to date, principally because public funding at the state level in Texas is available only to public fleets.

United Parcel Service

United Parcel Service (UPS) has been operating natural gas vehicles since 1989 and currently operates the largest private fleet of alternative fuel vehicles in the country. The current fleet includes more than 800 natural gas vehicles and continues to grow. UPS's natural gas vehicles are operating in cities all across the country including: Los Angeles, New York, Atlanta, Dallas, Oklahoma City, and Hartford. UPS also operates large propane fleets in Canada and Mexico.

Though UPS has clearly been a leader in the use of alternative fuels, the company has a large fleet and there is still room for improvement. For example, UPS operates more than 8,000 heavy-duty trucks running on diesel fuel. UPS needs to move aggressively to transition the heavy-duty portion of their fleet to alternative fuels.122

New York City Trash Trucks

In the fall of 1992, six new CNG trash trucks appeared on the streets of New York City. Over the next four years, the trucks accumulated more than 60,000 miles each in regular service in the New York City fleet. The average range of a CNG refuse hauler is about 60 miles in between fueling, as compared to the diesel version which can go as far as 95 miles. In terms of maintenance, the CNG trucks performed above expectations and the Department of Sanitation was delighted with them. The maintenance and repair database accumulated on the CNG trucks showed that they had been only slightly more expensive to maintain that the diesel trucks. In terms of emissions, oxides of nitrogen and carbon monoxide were sometimes less for the CNG trucks and other times less from the diesel trucks (these results were expected given the early CNG engine models used in the pilot program). Particulate matter, however, was cut dramatically by use of CNG - the levels were too low to measure in 6 of 11 tests performed by the National Renewable Energy Laboratory.123 According to New York City Department of Sanitation Manager Tim Harte, the Department has been pleased with its CNG experience. "Our drivers are satisfied with the horsepower and speed. And the vehicles are quieter and cleaner, there's no diesel knock, and there are no fumes."124

City Buses: The Mostly Good, Bad, and the Ugly

One way local government can help protect the public from potential diesel exhaust exposures is to power mss transit fleets with alternative fuels. Of the 3,406 buses built in 1996 for the US Market, 481 run on alternative fuels, and roughly one-fifth of the buses currently on order will be powered by natural gas, propane, electricity, or hydrogen.125 Probably the greatest success in alternative fuel transit buses has come with compressed natural gas (CNG) and, to a lesser extent, liquefied natural gas (LNG). Nearly 1,000 natural gas buses now operate in cities around the United States.126 Among the transit agencies that have reported major CNG successes are Pierce Transit in Tacoma, WA; RTD in Sacramento, CA; Los Angeles County Metropolitan Transportation Authority in Los Angeles, CA, and Sunline Transit in Palm Desert, CA.127 NRDC's own "Dump Dirty Diesel" Campaign in New York has succeeded in convincing New York's transit agencies to significantly shift their bus purchases from diesel to CNG. In the next few years, nearly 1,000 CNG and other clean-fuel buses will replace New York City's dirty diesels.

As mentioned above, zero-emission fuel cell technology holds great promise for a variety of heavy-duty applications beyond municipal transit buses. Though these buses are not yet available on the market, the world's largest bus manufacturer, Daimler Benz, is poised to mass produce them near the turn of the century. Chicago Transit Authority already has three fuel cell buses in operation powered by hydrogen, and Vancouver will be starting a demonstration project with three fuel cell buses later this year.128

The promise of fuel cells should not stop transit officials from purchasing the cleanest buses available today. Buses purchased this year will likely be on the road for more than 12 years. Transit agencies need to move now to purchase low polluting natural gas buses instead of diesel. Fortunately, over a dozen fleets have committed to purchase only natural gas buses, including Atlanta, Los Angeles, Cleveland, Toronto, Tacoma, Sacramento, Houston, and the N.Y.C. Department of Transportation. Once in place, the natural gas infrastructure can provide a bridge to the zero-polluting hydrogen fuel cell buses of the future.

Focus #7: Dumping Dirty Diesels in New York City

New York City is the nation's transit bus capital, with two of the nation's ten largest transit fleets - the Metropolitan Transportation Authority (MTA) operates a 3,500-bus fleet and the New York City Department of Transportation (NYC DOT) runs a 1,200-bus fleet. The New Jersey Transit shuttles, private tour buses, school buses, intercity buses, and trucks also add to the diesel mix. It is no wonder that New York City is the diesel emissions capital of the United States.

The New York State Department of Environmental Conservation estimates that 52.8 percent of the airborne particles found in Manhattan's street canyons come from diesel tailpipes.129 The health impacts of this concentration of particulates are potentially immense - over 4,000 premature deaths annually.130 With particle concentrations averaging roughly 50 µg/m³ on an annualized basis, the diesel exhaust concentration may be as high as 26.4 µg/m³ -- far higher than most American cities. This concentration of diesel exhaust is expected to potentially lead to a lifetime risk of 8 cancers among every thousand people exposed. Among the 1.5 million residents of Manhattan, this translates to approximately 8,500 additional cancer cases.131 Low-income communities and communities of color in northern Manhattan bear the brunt of the MTA's diesel bus fleet. Six of the MTA's seven Manhattan depots are in communities like Harlem and Washington Heights which sustain asthma rates that are 3-5 times the City average and among the highest in the nation.132

Thankfully, New York has begun an effort to clean-up its fleet. In 1996-1997, the MTA committed to converting three of its diesel bus depots to natural gas and to purchasing at least 500 clean-fuel buses over a five-year period. The NYC DOT fleet also added a bus order that could result in nearly 400 more natural gas buses. Each of these purchases will add to the approximately 100 natural gas buses that are already in service. But, while the MTA's clean-fuel bus program is making an exciting turn-around, New Yorkers cannot breathe easy yet.

First, the MTA has rejected calls to fully commit to clean fuels, and even proposed adding nearly 600 more diesel buses to its 5-year purchase plan. Second, despite significant progress in constructing natural gas programs for Brooklyn and the Bronx, the MTA has backpedaled on its commitment to build a Manhattan depot of approximately 200 natural gas buses. The MTA's promised 1997 date for selecting the depot site has passed and its construction target of 1999 has been pushed back to 2001. To make matters worse, the MTA recently closed one of its Bronx depots and plans to move those 200+ diesel buses to northern Manhattan, pushing those diesel emissions into the State's only PM10 non-attainment area.

Third, the MTA continues to cling to the fantasy that "cleaner diesel" is a possible answer to their pollution problem. The MTA is investing heavily in a diesel-fueled hybrid-electric bus program starting with 10 demonstration buses. While NRDC is encouraged by the improved efficiency and emissions reduction potential of hybrid-electric systems, we are concerned that a diesel hybrid-electric bus will only prolong New York's dependence on diesel.

The MTA must build on the past two years of progress and fulfill its potential to become the clean-fuel bus capital. NRDC's Dump Dirty Diesel Campaign is committed to insuring that this happens. We urge the MTA to take three immediate steps: First, the MTA must fully commit to phase out its diesel buses in favor of cleaner alternatives. Second, the MTA must re-commit to its original plan and timeline for converting a 200-bus depot in northern Manhattan to natural gas. Third, the MTA must abandon its efforts to use so called "clean diesel" to meet the air quality and public health needs of New York City. These critical steps will help make New York City's air healthier.

Alternative-Fuel Transit Buses Hit the Road

The market for alternative fuel transit buses has been developing for a decade and is very competitive. At least five manufacturers are selling the standard forty-foot transit buses configured to run on CNG or LNG. The manufacturers include New Flyer, Neoplan, Orion, North American Bus Industries (NABI) and NOVA. Most of the natural gas buses on the road or for sale today are powered by Cummins L10 or Detroit Diesel Series 50 engines, but recently John Deere has begun offering a CNG engine to compete in this growing market.

In the transit shuttle market, battery power is making the most progress among low-emission technologies. Santa Barbara, California and Chattanooga, Tennessee have had several years of success operating electric buses. Recently cities such as Santa Monica, CA have also begun operating electric shuttle buses. The Department of Energy's Heavy Vehicle and Engine Resource Guide (January 1998) lists more than 10 battery-powered electric bus models currently available for sale in the United States.

Clean Transit Success Stories

SunLine Transit Agency, Thousand Palms California

SunLine Transit Agency, a relatively small public transit property located in Thousand Palms, California, operated the second oldest fleet in the nation in 1992. The condition of the fleet was so bad, that SunLine management had a saying, "Old buses don't die -they come to SunLine!"133 SunLine's breakdown reputation finally compelled the board of directors to order a replacement of SunLine's fleet, but this time with alternative fuel vehicles. After sending management to Canada, Washington, DC, and Sacramento to collect research and talk to experienced alternative fuel operators, SunLine chose to power its fleet with compressed natural gas. SunLine received over $2 million from the Federal Transit Administration's Section 3 money, was awarded a $12 million procurement from local funding, partnered up with the Southern California Gas Company to develop a refueling station, and convinced a local community college to train its mechanics. In under 2 years, Sunline became the first transit agency in the nation to convert 100% of its fleet to CNG. According to a 1995 source, SunLine Transit covers an area approximately 58 miles long by 7 miles wide, transports 8,000 passengers per week day, and has logged over 63,000 annual miles per bus.134 Not only is SunLine's management happy with the fewer maintenance problems experienced with CNG in comparison to diesel and the lower fuel costs incurred, SunLine's general manager, Richard Cromwell III, concludes, "We believe we're enhancing our community's quality of life with cleaner air. Environmentally, CNG is simply the right thing to do."135

Sacramento Regional Transit District, Sacramento California

The Sacramento Regional Transit District has a long and extensive history using compressed natural gas transit buses in their operations. Their first CNG buses went into operation in 1993, and these buses have logged an average of 270,000 miles. While most of the agency's diesel fleet requires engine overhauls at 200,000 - 250,000 miles, the natural gas buses have not needed overhauls as yet and city officials hope to reach 300,000 (or more) miles before such overhauls are needed for their CNG buses. The RTD presently operates 136 Orion CNG buses with Cummins L10 engines out of a total fleet of 210, and intends to purchase 18 new CNG buses (twelve full-size and six 22-foot shuttles) in their next fiscal cycle. Sacramento RTD intends to convert their entire fleet to run on natural gas as soon as funding is available.

Not only are these buses much cleaner than their diesel counterparts, but they are much cheaper to operate as well. During the period from July 1, 1997 through March 31, 1998, the agency's CNG buses logged 4,594,009 miles compared with 1,801,411 for their diesel fleet.136 The agency estimates the total operational cost of their CNG buses for this period was approximately $.39 per mile, compared with $.47 for their diesel buses. Mark Lonergan, Assistant to the Chief Operating Officer, noted that the most telling thing about the agency's CNG buses is that they often go unnoticed, primarily because there is virtually no exhaust from these buses.

Pierce Transit, Tacoma Washington

Pierce Transit, based in Tacoma, Washington, began its CNG experience as far back in 1985 when it decided to test the alternative technology for its servicing needs. Ten years, a new facility and 58 CNG buses later, CNG is no longer a novelty; it's business as usual. Pierce Transit's operations cover an area of 450 square miles and a population of approximately 600,000 residents.137 The agency serves both rural and urban areas, including an express route to Seattle which operates exclusively on CNG. Maintenance costs for Pierce's CNG fleets are only slightly higher for CNG over diesel - by about 8 percent. However, fuel costs for CNG are lower than diesel. Reliability of the CNG and diesel fleets were identical based on the number of road calls per 1,000 miles and usage comparisons. Currently Pierce reports that it pays $30,000 to $50,000 more for a CNG bus than for its diesel counterpart, but this incremental cost is likely to change as both technology and economies of scale improve, and as Federal and state environmental regulatory agencies place increasingly stringent environmental standards on diesel engines. Ron Shipley, Pierce Transit's Director of Maintenance, notes, "If you think you're going to be in business 10 years from now, you should be looking at some other way to do business (other than diesel) that provides fuel price stability and availability as well as environmental improvements."138 By 2003, Pierce Transit plans to power all of its buses by CNG engines.

Los Angeles County and Orange County Transportation Authorities

The Los Angeles County Metropolitan Transportation Authority (LACMTA) is one of the country's leaders in operating alternative fuel buses. In 1993, the LACMTA Board adopted an Alternative Fuel Initiative policy, committing to purchase only clean alternative-fueled buses. Today, LACMTA is operating 420 CNG buses in a fleet of 2,160 buses. The transit agency has 400 CNG buses on order and is about to request bids for 215 more. LACMTA has four CNG refueling stations in operation and will have two more completed by early 1999.

Until recently, LACMTA had been operating approximately 320 buses on alcohol fuels -- ethanol and methanol. Unfortunately the agency's excellent record on purchasing new clean buses is tarnished by its recent decision to convert approximately 125 of its alcohol buses to diesel in response to some operational problems. LACMTA staff have indicated that the agency will probably continue to operate 100-150 buses on methanol and approximately 50 buses on ethanol.

In February 1998, neighboring Orange County Transportation Authority (OCTA) approved the purchase of 186 liquefied natural gas (LNG) buses to be delivered over the next three years. The OCTA plans to phase out diesel fuel buses from its fleet by the year 2010.139

Focus #8: Foggy Reasoning Plagues San Francisco Muni

Unfortunately, the San Francisco Municipal Railway (Muni), a transit authority that has a great opportunity to improve the Bay Area's air quality by replacing its aging diesel fleet with alternative fuels, has been sluggish to move away from diesel. Transit agencies are both a mobile and stationary source for diesel exhaust. For example, Muni maintains three diesel bus yards and a maintenance facility in and around low income residential areas. Muni defends its recent purchase of 280 new diesel buses by saying that it has done enough to provide environmentally cleaner public transportation by electric bus and rail, and that emission levels from the new "clean diesel" buses are "equal to that of compressed natural gas and meet 1998 U.S. EPA regulations."140 However, as we note above, this view is mistaken and, in fact, so called "clean diesel" buses are more than twice as polluting as their CNG equivalents and pose high cancer risks. Although Muni's electric fleet does deserve praise, the transit authority has missed the bus on diesel emissions. Transit authorities, like Muni, need to use the alternative fuel options available and eliminate the use of diesel.

Clean Buses for Kids

In light of children's heightened vulnerability to diesel exhaust pollution, the transition to cleaner alternative fuels seems especially appropriate for the legions of school buses providing daily transportation for millions of our children. Although the vast majority of school buses remain dependent on diesel engines, an increasing number of school bus fleet managers are discovering the benefits -- both environmental and economic -- of alternative fuels. Compressed natural gas seems to hold the greatest promise for alternative fuel school bus applications in the near term.

Natural gas school buses are currently available from major manufacturers including Blue Bird, Thomas and Navistar. Manufacturers of natural gas engines include Cummins, Detroit Diesel and John Deere. Blue Bird and Thomas also offer battery-powered electric school buses.

Antelope Valley Schools Transportation Agency, Lancaster California141

Located roughly 60 miles northeast of Los Angeles, the Antelope Valley Schools Transportation Agency (AVSTA) operates a fleet of school buses and special-education vans that transport students in four school districts covering 1,700 square miles. In the early 1990's, AVSTA accumulated several thousand dollars in fines for violating strict California vehicle emissions regulations. In 1992, Ken McCoy, AVSTA's Chief Executive Officer, found alternative fuels to offer a solution to this problem. McCoy combined grants from the California Energy Commission, the South Coast Air Quality Management District, SoCal Gas, and others to purchase an alternative fuel school bus fleet and build on-site fueling stations. AVSTA now operates 31 CNG buses and 16 methanol buses which have significantly reduced emissions from the fleet. McCoy vests the most confidence in his CNG buses, stating: "If I were choosing fuel, it would be CNG only, based on the bottom line."

Lower Marion School District, Ardmore Pennsylvania142

Michael Andre, Supervisor of Pupil Transportation for the Lower Marion School District (LMSD), located in Ardmore, PA (a Philadelphia suburb), reports that his CNG school buses are safe, clean, quiet, and dependable. LMSD operates a fleet of 81 school buses, 27 of which are powered by CNG. In 1993, LMSD decided to switch from diesel to CNG power in response to community concerns about the noise and pollution generated by the District's diesel school bus fleet, which is housed in a facility located in a quiet, residential neighborhood. After investigating several alternative fuels, LMSD determined that CNG offered the best combination of economic feasibility and pollution reduction. The District used State grants to purchase the CNG buses. The buses have demonstrated, through years of service, that they are dependable and safe. Mr. Andre emphasizes his CNG buses' emissions reductions compared to their diesel counterparts: NOx reduced by 87 percent, PM virtually eliminated, carbon monoxide (CO) reduced by 69 percent; non-methane organic gases reduced by 87 percent; and carbon dioxide reduced by 20 percent.


* Assuming a typical urban bus travels 630,000 mile over its 12-lifetime (based on CARB's MVE17G mobile source emissions model). These values include estimates of the higher emissions released in a vehicle's latter years because of deterioration. For all engine technologies, however, actual reductions will vary from case to case.

** Assuming a typical urban bus an average of 52,000 miles per yar (CARB's MVE17G model input), while a car travels roughly 10,600 miles per year (ORNL 1997). Emissions for the average passenger car in calendar year 1998 were calculated based on runs of MVE17G for the South Coast Air Basin. These estimates are 1.026 g/mi (NOx)and 0.027 g/mi (PM): CARB MVE17G Version 1.0. October 4, 1996.

*** The Caterpiller dual fuel technology utilizes diesel and natural gas simultaneously, using diesel compression to ignite the natural gas. Using diesel ignite obviates the need for spark plugs, and allows these engines to take advantage of diesel efficiencies. While still only used in a few fleets nationally, early tests suggest that this duel fuel technology will allow alternative fuels to penetrate higher horsepower vehicles, and operate more efficiently than dedicated natural gas engines. Moreover, the Caterpillar C-10 was the first engine to be certified to the California Air Resources Board's optional 2.5g/bhp-hr low-NOx standard, although Cummins has since certified three engine families to this standard (with optional 2.5g/bhp-hr low-NOx).

**** Since LNG has to be cooled to -260 degrees Fahrenheit, there is always an issue of the fuel increasing in temperature, despite its being stored on vehicles in double steel-lined cylinders. If the temperature does increase, the LNG expands and pressure increases in the cylinder, requiring the venting of the fuel. While natural gas is non-toxic and has a high ignition temperature (meaning low risk of flammability), venting fuel can reduce the cost-effectiveness of natural gas options.

113. United States Environmental Protection Agency. Heavy-Duty Highway Engines - CI and Urban Buses. 1998.

114. Calstart. "Hydrogen Buses Now Serving on Chicago Routes." News Notes. Issue 98-12F. March 27, 1998.

115. For more information, please see AB1368 and SB1857.

116. For more specific information, see the U.S. Department of Energy's Heavy Vehicle and Engine Resource Guide, available from the U.S. Department of Energy at 800.423.1DOE or their Website at www.afdc.doe.gov.

117. Memo from Caterpillar Inc. to Mr. Robert Shepherd, Power Systems Associates, dated March 3, 1997, states that a 1000 hour duel fuel durability test found that fuel consumption was 86.9% natural gas and 13.1% diesel.

118. "Grocery Chain Puts LNG Tractors on California Road", Alternative Fuels in Trucking, August 1997, Volume 6, Issue 1, Page 3; Raley's LNG Truck Fleet Start-Up Experience, National Renewable Energy Laboratory, DOE [hereinafter referred to as "NREL report on Raley's"].

119. NREL report on Raley's, p. 2.

120. "LNG: A Report from the Field", Fleet Equipment Magazine, August 1997

121. Text based on conversations with Troy Retzloss, Fleet Manager of HEB Groceries.

122. For more information regarding the UPS alternative fuel fleet, please visit their website at http://www.ups.com/about/inits.html.

123. National Renewable Energy Laboratory. "Alternative Fuel Trucks Case Studies: Running Refuse Haulers on Compressed Natural Gas. Golden, Colorado. 1996. p. 6-7.

124. National Renewable Energy Laboratory. "Alternative Fuel Trucks Case Studies: Running Refuse Haulers on Compressed Natural Gas. Golden, Colorado. 1996. p. 1.

125. American Public Transit Association (APTA). 1997. Transit Vehicle Data Book. Washington, DC: APTA. May.

126. Larson, James. 1997. "Natural Gas Fueling Options for the Transit Market." Presentation to the San Francisco Municipal Railway.

127. Remillard, Richard. 1997. "A Framework for Evaluating Fuel Options for transit Buses (Overview of TCRP Project C-8)." APTA Alternate Fuels Committee meeting. Nashville, Tenn. August.

128. Mark, Jason, and Lawrence R. Davis. 1998. Shifting Gears: Advanced Technologies and Cleaner Fuels for Transit Buses. Union of Concerned Scientists: Cambridge, Massachusetts. P. 18-21.

129. NYS DEC, State Implementation Plan for Inhalable Particulate (PM10), September 1995, p.9 and Appendix A-3.

130. Breath-Taking, p. 66

131. Estimate based on California EPA's Science Review Panel unit cancer risk of 3 x 10-4, announced at a public meeting on April 22, 1998, and on Dawson, et. al., Proposed Identification of Diesel Exhaust as a Toxic Air Contaminant, Part B: Health Risk Assessment for Diesel Exhaust. Public and Scientific Review Panel Review Draft, February 1998, pp. 1-8 - 1-9. [(3 x 10-4) x (26.4) = 0.008 (or 8 in one thousand)].

132. According to the NYC Department of Health and West Harlem Environmental Action, the NYC average asthma hospitalization rate in 1992 was 8.0 per 1,000 people. Harlem's asthma hospitalization rates ranged from 12.4 to 28.9 per 1,000 people.

133. Passenger Transport. 1996. "Sunline Takes Challenge of Implementing All-CNG Fleet. Vol. 54(19). American Public Transit Association : Washington DC.

134. SunLine Transit Agency. 1995. "An Overview." Thousand Palms, CA. Pp. 1-2.

135. Passenger Transport. 1996. "Sunline Takes Challenge of Implementing All-CNG Fleet. Vol. 54(19). American Public Transit Association : Washington DC.

136. Bus Maintenance Monthly Status Report, April 1998.

137. National Renewable Energy Laboratory (NREL). "The Pierce Transit Success Story..." Department of Energy. October 1996. p. 1.

138. NREL October 1996. p. 7.

139. Los Angeles Times. "County Aims to Make Clean Sweep of Bus Fleet." Orange County Edition. February 18, 1998.

140. Letter from Mayor Willie L. Brown, Jr. to a local constituent dated February 2, 1998.

141. Argonne National Laboratory, "Alternative-Fuel Buses Earn High Marks from Antelope Valley Schools," published for the U.S. Department of Energy, January 1998, information also based on conversations with Ken McCoy, Chief Executive Officer, AVSTA.

142. Text based on conversations with Michael Andre, Supervisor of Pupil Transportation, LMSD.

All Tags [ View Popular Tags ]:
AB 1493
AB 32
air pollution
air toxics
Arctic National Wildlife Refuge
boreal forest
California environmental legislation
cap 2.0
cap and trade
carbon footprint
carbon offsets
carbon pollution
case studies
causes of global warming
Clean air
Clean Air Act
clean energy
clean energy economy
clean vehicles
climate change
climate legislation
coal-fired power plants
compact fluorescent lighting
compact fluorescents
computer equipment
conservation and restoration
consumer products
cover crop
Danielle Droitsch
data centers
demand side management
diesel buses
diesel exhaust
dirty fuels
efficient light bulbs
efficient vehicles
electric cars
electric utilities
electric vehicles
electricity and natural gas utlities
energy efficiency
energy efficiency standard
energy efficient buildings
energy efficient light bulbs
energy effiency
energy plan
energy policy
energy security
energy-efficient bulbs
environmental history
environmental protection agency
fish & fishing
fracking risks
fuel economy
fuel efficiency
fuel efficiency standards
fuel savings
gas drilling
gas prices
global warming
global warming and the economy
global warming emissions
global warming legislation
global warming pollution
green building
green buildings
green business
green jobs
green sports
greenhouse gas emissions
gulf of mexico
halogen bulbs
halogen lightbulbs
health effects
home energy
home networks
household energy use
human health
Hurricane Katrina
hybrid cars
hybrid electric vehicles
hybrid vehicles
hydraulic fractring
hydraulic fracturing
incandescent lighbulbs
incandescent light bulbs
India Initiative
indoor air quality
infrastructure efficiency
Keystone XL
Kids' Health
Latin America
light bulbs
light emitting diodes
liquid coal
livestock farms
location efficiency
Los Angeles
Marcellus Shale
Middle East
mountaintop removal mining
natural gas
natural gas drilling
New York
nitrogen oxides
North Dakota
Northeast states
nrdc offices
nuclear energy
offshore drilling
offshore oil
oil and gas industry
oil consumption
oil dependence
oil drilling
oil imports
oil shale
oil spill
oil spills
open space
particulate pollution
Persian Gulf
power plants
public lands
public transportation
regional greenhouse gas initiative
regulatory reform
renewable energy
renewable fuel
residential small networks
respiratory illness
Rocky Mountains
SB 315
server rooms
smart biomass
smart grid
smart growth
smog air pollution
solar power
sulfur dioxide
sustainable sourcing
tar sands
tar sands pipeline
tar sands; keystone xl
tax incentives
tax subsidies
toxic waste
transportation bill
vehicle emissions
water efficiency
water management
Water Pollution
western water
what you can do
wind power
wind turbines

Sign up for NRDC's online newsletter

See the latest issue >

Give the Gift That Will Make a Difference: Renewable Reality

NRDC Gets Top Ratings from the Charity Watchdogs

Charity Navigator awards NRDC its 4-star top rating.
Worth magazine named NRDC one of America's 100 best charities.
NRDC meets the highest standards of the Wise Giving Alliance of the Better Business Bureau.

Donate now >

Related Stories

Efficient Appliances Save Energy -- and Money
A consumer's guide to buying energy efficient appliances and electronics.
Share | |