Natural gas is best known as the fuel that heats our homes, cooks our food, and in some cases, produces our electricity. But natural gas is also successfully being used today in cars, trucks, and buses as a cleaner fuel alternative to diesel and gasoline. Compared to conventional diesel and gasoline, natural gas results in less tailpipe pollution and reduces our oil dependence. Here are some frequently asked questions about natural gas and its use as a transportation fuel.

1. Where does natural gas come from?
2. Which vehicles are best suited for natural gas?
3. Are there emissions benefits from using natural gas in vehicles?
4. Do new pollution controls make diesel engines as clean as natural gas?
5. What is the cost of owning and operating a natural gas vehicle?
6. Are natural gas vehicles safe?
7. Do natural gas vehicles help combat global warming?
8. Are there other benefits to using natural gas as a transportation fuel?

Where does natural gas come from?
Over 99% of the natural gas used in the U.S. comes from domestic or other North American sources. However, increasing demand for natural gas will require new supplies from non-North American countries, increasing our dependence on foreign sources. The Energy Information Administration (EIA) predicts that by 2025, more than 15% of our natural gas supplies will be imported from countries other than Canada and Mexico.¹ Almost all of today’s natural gas is fossil based, non-renewable, and requires drilling and non-traditional extraction techniques that can be environmentally damaging. Biogas, or gas produced from plant material and solid waste, can be used in place of natural gas. Many municipal waste managers have begun capturing landfill gas to generate electricity or sell directly to commercial customers, but sources are limited. 
 

		in clean vehicles    Alternative Fuel School Buses      Diesel Engines & Public Health

Are there emissions benefits from using natural gas in vehicles?
Yes. For heavy trucks and buses, a new (Model Year 2004) natural gas vehicle can cut toxic soot pollution by 75 to 90 percent, while smog-forming pollution is reduced by about 25 percent compared to conventional diesel. Diesel soot is extremely toxic, containing over 40 chemicals that California has declared as toxic air contaminants. The California Air Resources Board (CARB) estimates that diesel exhaust causes 70% of the state’s cancer risk from airborne pollution. 

For passenger vehicles, natural gas also offers emissions benefits. For example, Honda’s 2004 Civic GX runs on compressed natural gas (CNG) and as of January 1 of this year is the cleanest federally certified passenger vehicle available, with the exception of zero emission electrified vehicles.³ It is also one of a handful of vehicles including gasoline and hybrid electric vehicles that meet California’s strictest emissions standards.⁴ Another emissions benefit of natural gas vehicles is that there are no evaporative emissions during refueling.

Do new pollution controls make diesel engines as clean as natural gas?
Just about, though natural gas remains a cleaner alternative today. It is true that new pollution controls show the potential to reduce toxic soot pollution from both diesel and natural gas engines. Properly functioning particulate traps for diesel engines and oxidation catalysts for natural gas engines cut toxic emissions to very low levels. The California Air Resources Board conducted a study comparing compressed natural gas and diesel transit bus emissions and found that diesel engines with particulate traps can lower soot emissions to levels comparable to natural gas engines with no pollutions controls. Uncontrolled natural gas bus engines do have higher emissions of formaldehyde than diesel engines, but these can be reduced over 95% with an oxidation catalyst, an exhaust emission control device. Use of an oxidation catalyst also further reduces soot and some smog forming emissions from natural gas engines. Natural gas engines need to use oxidation catalysts to maintain an emissions advantage over the cleanest diesel engines with the latest emission controls.
 
Unfortunately, nitrogen oxides (NOx) are more difficult to control, and NOx emissions are still higher from the average diesel engine than from the average natural gas engine. In order to function, new pollution controls for diesel require the use of a special low-sulfur fuel, which will not be nationally accessible until mandated by federal law in 2006. Plus, these pollution control technologies must still be monitored to prove their effectiveness over the range of real-world operating conditions. If they fail, degrade, or are disengaged, diesel engines will continue to pollute.

What is the cost of owning and operating a natural gas vehicle?
Because of low volume production, passenger natural gas vehicles tend to be about $3,000 to $6,000 more than equivalent gasoline vehicles, while heavy-duty natural gas buses cost about $30,000 to 40,000 more than equivalent diesel buses.⁵ Some fleet operators report that these costs can be recouped by lower operating costs, which are a combination of maintenance costs, fuel costs, and the fuel economy of the vehicle.⁶ Compared to diesel fleets, maintenance costs of natural gas fleets have varied widely across the country, with some fleets reporting lower or equivalent maintenance costs and others experiencing higher costs.

Historically, natural gas has been less costly than diesel and gasoline, but natural gas prices have been volatile over the past few years. The EIA estimates that natural gas prices may get some relief in the short term, but will continue to creep up over the next 20 years due in large part to increased demand from new natural gas fired power plants. Natural gas demand for transportation is also expected to increase significantly, but is projected to remain well under 1 percent of total U.S. natural gas consumption. On average, CNG is expected to remain less costly on a gasoline gallon equivalent basis than diesel or gasoline.⁷   

Are natural gas vehicles safe?
Although both natural gas and diesel fuels are flammable and require special precautions and fire protection equipment, natural gas lacks some of the risks of diesel or gasoline. In fact, DOE reports that natural gas fuel tanks are much stronger and safer than either diesel or gasoline fuel tanks.⁸ Diesel and gasoline tanks can leak and contaminate groundwater, which is not a risk with natural gas. Diesel bus facilities often store much larger quantities of fuel on site than natural gas facilities. And, while natural gas vapors are nontoxic, diesel vapors contain toxics that are dangerous to ingest or breathe.

Do natural gas vehicles help combat global warming?
It has been estimated that CNG (Compressed Natural Gas) vehicles using North American natural gas achieve green house gas emission reductions in the range of 5 to 25 percent compared to conventional passenger gasoline vehicles.⁹ Use of non-North American natural gas would all but eliminate the green house gas reductions because of emissions associated with transportation of liquid natural gas in large ocean tankers.¹⁰ 
 
Are there other benefits to using natural gas as a transportation fuel?
Increased use of natural gas for transportation applications will require infrastructure investments, laying the groundwork for the future introduction of fuel cell vehicles. Experience with gaseous fuels and infrastructure can facilitate a transition to a future hydrogen transportation system. In addition, demonstration projects are proceeding that use a blend of hydrogen and natural gas in transit buses, both reducing smog forming pollutants and introducing hydrogen as a transportation fuel.¹¹ 

Notes

(1) Energy Information Agency, U.S. Department of Energy, Annual Energy Outlook 2004 with Projections to 2025, DOE/EIA-0383(2003), January 2004.

(2) FuelMaker Corporation, www.fuelmaker.com

(3) Meets EPA’s Tier II bin 2 emissions standard.

(4) U.S. Environmental Protection Agency, Certified Vehicle Test Result Report Data, January 2004

(5) According to U.S. Department of Energy Clean Cities Vehicle Buyer’s Guide for Consumers, http://www.ccities.doe.gov/vbg/consumers/

(6) Sacramento Regional Transit District (SRTD) and SunLine Transit Agency (STA). 1999. Three Year Comparison of Natural Gas and Diesel Transit Buses. Revised August. Thousand Palms, Calif.: SunLine Transit Agency.

(7) [See note 1]

(8) National Renewable Energy Laboratory, U.S. Department of Energy, Natural Gas Buses: Separating Myth from Fact, NREL/FS-540-28377, May 2000.

(9) Wang, M.Q. and H.S. Huang, A Full Fuel-Cycle Analysis of Energy and Emissions Impacts of Transportation Fuels Produced from Natural Gas, Center for Transportation Research, Energy Systems Division, Argonne National Laboratory, December 1999.

(10) General Motors Corporation, et al., Well-to-Tank Energy Use and Green House Gas Emissions of Transportation Fuels – North American Analysis, June 2001.

(11) National Renewable Energy Laboratory, U.S. Department of Energy, The Next Generation Natural Gas Vehicle Activity,  DOE/GO-102003-1779, September 2003.