Plug-In Hybrid Electric Vehicle Benefits

Plug-in hybrid electric vehicles (PHEVs) promise many benefits for consumers, fleets, and the nation. These advanced vehicles have the potential to cut fuel use and costs, increase U.S. energy security, protect public health and the environment, and enhance the U.S. electrical system. Government and industry research and development are overcoming the barriers to realizing these benefits.

Cutting Fuel Use and Costs

Electricity typically costs much less than gasoline or diesel fuels. Because PHEVs use electric power much of the time, and the batteries are recharged by plugging into the electrical grid, they can significantly reduce fuel use and costs. For example, if electricity costs $0.08 per kilowatt-hour and gasoline costs $2.77 per gallon, a PHEV could drive on electric power for 3 cents per mile compared with 13 cents per mile for driving on gasoline. Combined operation might result in a cost of about 6 to 8 cents per mile.

Plug-in hybrid electric vehicles also offer flexible fueling options. Because PHEVs can be recharged at home much of the time, drivers can limit their trips to the gas station.

Increasing Energy Security

The United States imports more than 60% of its petroleum, two thirds of which is used to fuel vehicles in the form of gasoline and diesel. The demand for petroleum imports is increasing. With much of the worldwide petroleum reserves located in politically volatile countries, the United States is vulnerable to supply disruptions.

Plug-in hybrid electric vehicles are highly efficient—requiring little petroleum-based fuel to drive—and can use electricity derived from domestic fossil fuel, nuclear, and renewable sources. PHEVs also could be designed to use renewable and domestically produced alternative fuels instead of gasoline or diesel, further reducing U.S. reliance on imported petroleum.

Protecting Public Health and the Environment

Electricity is an energy carrier rather than a primary energy source. Thus, the environmental benefits of PHEVs depend in part on the source of electricity from which the PHEVs are charged. If the electricity comes from efficient power plants, the benefits can be substantial. One U.S. study projected an average 42% carbon emissions reduction from mileage driven on electricity instead of gasoline. Even transferring the point of emissions from the tailpipe to the power plant could be important for urban areas with severe automobile-related air quality problems.

Hybrid vehicles have additional features that make them more environmentally friendly than conventional vehicles. See Hybrid Electric Vehicle Benefits to learn how hybrid systems reduce pollutant emissions.

Enhancing the Electrical System

Plug-in hybrid electric vehicles have the potential to enhance the nation's electrical generation and distribution system. Electrical demand varies greatly; demand is generally high during the day and low at night. Charging PHEV batteries at night would take advantage of the low demand. If vehicle-to-grid capabilities are developed, PHEV battery capacity also could be used to help meet peak electricity demands. PHEV drivers would charge their vehicles while demand and electricity prices are low and, when their vehicles are idle, sell electricity back to the utility when demand and prices are high. This could help utilities avoid building extra generation capacity to meet peak demands.

How Hybrids Work

Hybrid-electric vehicles (HEVs) combine the benefits of gasoline engines and electric motors and can be configured to obtain different objectives, such as improved fuel economy, increased power, or additional auxiliary power for electronic devices and power tools.

Some of the advanced technologies typically used by hybrids include

Regenerative Braking. The electric motor applies resistance to the drivetrain causing the wheels to slow down. In return, the energy from the wheels turns the motor, which functions as a generator, converting energy normally wasted during coasting and braking into electricity, which is stored in a battery until needed by the electric motor.

Electric Motor Drive/Assist. The electric motor provides additional power to assist the engine in accelerating, passing, or hill climbing. This allows a smaller, more efficient engine to be used. In some vehicles, the motor alone provides power for low-speed driving conditions where internal combustion engines are least efficient.

Automatic Start/Shutoff. Automatically shuts off the engine when the vehicle comes to a stop and restarts it when the accelerator is pressed. This prevents wasted energy from idling.

Airports

Airports provide many opportunities for alternative fuel and advanced technology vehicles and have demonstrated many implementation successes. Airports are uniquely suited for these vehicles for many reasons. The duty cycles of airport vehicles feature high mileage, long idle times, and frequent stopping. Vehicles that travel to and from airports are conducive to central refueling. There are a variety of fleets and applications with many alternative fuel and advanced vehicle options, and there are many sources of outside funding for vehicle and infrastructure projects.

This page serves as the table of contents for the Airports section. Use the links below to learn more about alternative fuel and advanced technology vehicles in airport fleet applications.

Airport Benefits

Alternative fuel and advanced technology airport vehicles provide important benefits, including the following:

* They protect public health and the environment around the airport by producing fewer emissions compared with conventional vehicles.
* They can reduce airport operational and maintenance costs while displacing petroleum use.
* Their fueling infrastructure adds a potential revenue stream.
* They enhance the public image of airports and associated businesses when they are cleaner, quieter, and "greener" than conventional vehicles.
* They can be eligible for state and federal incentives and other funding opportunities, including a number that are exclusive to airport applications. See the Federal Aviation Administration's Voluntary Airport Low Emissions (VALE) Program.

Why is fuel economy important?

Saves You Money

You can save $200-$1,500 in fuel costs each year by choosing the most efficient vehicle that meets your needs. This can add up to thousands of dollars over a vehicle’s lifetime. Fuel-efficient models come in all shapes and sizes, so you don't have to sacrifice utility or size.

You can also increase the fuel economy of you current vehicle by adopting good driving habits and maintaining your vehicle.

Strengthens National Energy Security

Better fuel economy can reduce our dependence on foreign oil.

More than half of the gasoline we put in our cars comes from oil imported from other countries.

Petroleum imports cost us over $5.2 billion a week—that’s money that could be used to fuel our own economy.

Protects the Environment

Burning fossil fuels such as gasoline or diesel contributes to a number of environmental problems, such as air pollution (smog) and global climate change. In addition, spills from refining and transporting oil and petroleum products damage ecosystems and pollute groundwater and streams.

Conserves Resources

Almost all of the cars and trucks we drive run on fuels derived from oil. Oil is a non-renewable resource, and while there is some debate as to how long this resource will last, we will eventually have to find new ways to power highway vehicles. Until other alternatives are developed, it makes sense to use fossil resources such as oil more efficiently to buy time to develop new and better energy sources and to make the transition to these sources smoother and less expensive.

What is a plug-in hybrid electric vehicle?

Plug-in hybrid electric vehicles (PHEVs) can be charged with electricity like pure electric vehicles and run under engine power like hybrid electric vehicles. The combination offers increased driving range with potentially large fuel and cost savings, emissions reductions, and other benefits.

Plug-in hybrid electric vehicles currently do not qualify as alternative fuel vehicles under the Energy Policy Act of 1992. However, they do qualify for incentives.

Plug-in hybrid electric vehicles are still at a pre-commercial stage of development. Research and development efforts are bringing them closer to widespread commercialization.

How Plug-in Hybrid Electric Vehicles Work

Like hybrid electric vehicles, PHEVs are powered by two energy sources—an energy conversion unit (such as an internal combustion engine or fuel cell) and an energy storage device (usually batteries).

The energy conversion unit can be powered by gasoline, diesel, compressed natural gas, hydrogen, or other fuels. The batteries can be charged by plugging into a standard 110-volt electrical outlet—a capability conventional hybrid electric vehicles do not have—in addition to being charged by the energy conversion unit when needed.

Plug-in hybrid electric vehicles have a larger battery pack than conventional hybrid electric vehicles. During typical daily driving, most of a PHEV's power comes from the stored electricity. For example, a PHEV driver might drive to and from work on all-electric power, plug in the vehicle to charge it at night, and be ready for another all-electric commute in the morning. However, the engine can be used when longer trips are required, and the PHEV does not need to be plugged in to operate.

Vehicle-to-Grid Concept

Researchers are developing "vehicle-to-grid" technologies that allow a two-way connection between the plug-in hybrid electric vehicle and the local utility grid. While the vehicle is plugged in and not in use, the utility could take advantage of the extra electrical storage capacity in the vehicle batteries to help meet peak electricity demand, provide grid support services, or respond to power outages. PHEV owners could get "paid" by the utility for use of their vehicles, which would only be used when needed and without negative effects on the vehicle battery's state of charge.

What is biogas?

Biogas is the gaseous product of the anaerobic digestion (decomposition without oxygen) of organic matter. It is typically made up of 50-80% methane, 20-50% carbon dioxide, and traces of gases such as hydrogen, carbon monoxide, and nitrogen. In contrast, natural gas is typically made up of more than 70% methane, with most of the rest being other hydrocarbons (such as propane and butane) and only small amounts of carbon dioxide and other contaminants. Biogas is sometimes called swamp gas, landfill gas, or digester gas. When its composition is upgraded to a higher standard of purity, it can be called renewable natural gas.

Biogas is used for many different applications worldwide. In rural communities, small-scale digesters provide biogas for single-household cooking and lighting. China alone is estimated to have 8–17 million of these systems. Large-scale digesters provide biogas for electricity production, heat and steam, chemical production, and vehicle fuel. In 2003, the United States consumed 147 trillion btu of energy from landfill gas, about 0.6% of total U.S. natural gas consumption.

Biogas as an Alternative Fuel

Once upgraded to the required level of purity (and compressed or liquefied), biogas can be used as an alternative vehicle fuel in the same forms as conventionally derived natural gas: compressed natural gas (CNG) and liquefied natural gas (LNG).

A 2007 report estimated that 12,000 vehicles are being fueled with upgraded biogas worldwide, with 70,000 biogas-fueled vehicles predicted by 2010. Europe has most of these vehicles. Sweden alone reports that more than half of the gas used in its 11,500 natural gas vehicles is biogas. Germany and Austria have established targets of 20% biogas in natural gas vehicle fuel. For more information on Europe's biogas vehicle activities, see the papers Biogas Upgrading and Utilization as Vehicle Fuel and The Future of Biogas in Europe:

In the United States, biogas vehicle activities have been on a smaller scale. Examples include a landfill in Whittier, California, that fuels vehicles with CNG derived from the landfill (also see the EPA's Clean Fuel Facility page) and an Orange County, California, landfill that produces LNG for use in transit buses.

What is a hybrid electric vehicle?

Hybrid electric vehicles (HEVs) typically combine the internal combustion engine of a conventional vehicle with the battery and electric motor of an electric vehicle. The combination offers low emissions, with the power, range, and convenient fueling of conventional (gasoline and diesel) vehicles—and HEVs never need to be plugged in.

Hybrid electric vehicles of the future could use alternative fuels such as biodiesel, natural gas, or ethanol. The flexibility of HEVs makes them well suited for fleet and personal transportation. Learn more about the components of a hybrid system.

Hybrid electric vehicles currently do not qualify as alternative fuel vehicles under the Energy Policy Act of 1992. However, they do qualify for incentives and provide several important benefits. Learn about currently available HEVs.

How Hybrid Electric Vehicles Work

Hybrid electric vehicles are powered by two energy sources—an energy conversion unit (such as an internal combustion engine or fuel cell) and an energy storage device (such as batteries or ultracapacitors). The energy conversion unit can be powered by gasoline, diesel, compressed natural gas, hydrogen, or other fuels.

Hybrid electric vehicles have the potential to be two to three times more fuel-efficient than conventional vehicles. HEVs can have a parallel design, a series design, or a combination of the two.

Fuel Economy Benefits

Increasing vehicle fuel economy benefits drivers by saving them money, the United States by making it less dependent of foreign oil, and the environment by releasing fewer emissions into the air.

Fuel Savings

Saving Money: photo of a hand putting money into a piggy bank.

The primary benefit of employing fuel economy measures is decreased fuel costs. Consumers and fleets can save $300 to $500 each year by driving the most fuel-efficient vehicles in a particular class. Over a vehicle's lifetime, fuel efficiency can add up to savings of thousands of dollars. Fuel-efficient models come in all shapes and sizes, so there's no need to sacrifice utility or size.

Consumers and fleets don't need to buy a new vehicle to increase their fuel economy. Proper maintenance and practical driving techniques can increase the fuel economy of their current vehicles.

The first thing to do is check your tire pressure. A vehicle running on tires that are properly inflated gets better gas mileage. Also be sure to keep your vehicle fluids up to standards. Next, consider your driving habits. Do you speed up to stop signs and hit the brakes hard? Do you make jackrabbit starts? If so, change your driving style and slow down sooner for stop lights and ease up to speed after the stop position. These simple changes can save you money and maybe even extend the life of your vehicle.

To appreciate these savings, try tracking your fuel economy for two weeks. The first week, check your odometer then drive as you usually do. At the end of the week, note the amount of gas you used that week and how many miles you got to the gallon. The following week, check your odometer again then employ the tips mentioned above. At the end of the second week, compare the mileage. Chances are you will see improved mileage during week two.

What is a fuel cell vehicle?

Fuel cell vehicles use a completely different propulsion system than conventional vehicles, which can be two to three times more efficient. Unlike conventional vehicles, they produce no harmful exhaust emissions—their only emission is water. Other benefits include increasing U.S. energy security and strengthening the economy.

Fuel cell vehicles are fueled with hydrogen, which is considered an alternative fuel under the Energy Policy Act of 1992 and qualifies for alternative fuel vehicle tax credits.

Fuel cell vehicles are still at an early stage of development. Research and development efforts are bringing them closer to commercialization.

How Fuel Cell Vehicles Work

Like electric vehicles, fuel cell vehicles use electricity to power motors located near the vehicle's wheels. In contrast to electric vehicles, fuel cell vehicles produce their primary electricity using a fuel cell. The fuel cell is powered by filling the fuel tank with hydrogen.

The most common type of fuel cell for vehicle applications is the polymer electrolyte membrane (PEM) fuel cell. In a PEM fuel cell, an electrolyte membrane is sandwiched between a positive electrode (cathode) and a negative electrode (anode). Hydrogen is introduced to the anode and oxygen to the cathode. The hydrogen molecules travel through the membrane to the cathode but not before the membrane strips the electrons off the hydrogen molecules.

The electrons are forced to travel through an external circuit to recombine with the hydrogen ions on the cathode side, where the hydrogen ions, electrons, and oxygen molecules combine to form water. The flow of electrons through the external circuit forms the electrical current needed to power a vehicle. See an animation of the process.

Fuel cell vehicles can be fueled with pure hydrogen gas stored directly on the vehicle or extracted from a secondary fuel—such as methanol, ethanol, or natural gas—that carries hydrogen. These secondary fuels must first be converted into hydrogen gas by an onboard device called a reformer. Fuel cell vehicles fueled with pure hydrogen emit no pollutants, only water and heat. Vehicles that use secondary fuels and a reformer produce only small amounts of air pollutants.

Fuel cell vehicles can be equipped with other advanced technologies to increase efficiency, such as regenerative braking systems, which capture the energy lost during braking and store it in a large battery.

How Natural Gas Vehicles Work

Light-duty natural gas vehicles work much like gasoline-powered vehicles with spark-ignited engines. This schematic shows basic CNG fuel system components.

CNG enters the vehicle through the natural gas fill valve (A) and flows into high-pressure cylinders (B). When the engine requires natural gas, the gas leaves the cylinders and passes through the master manual shut-off valve (C). The gas travels through the high-pressure fuel line (D) and enters the engine compartment. Gas enters the regulator (E), which reduces the gas pressure used for storage (up to 3,600 psi) to the required vehicle fuel injection system pressure. The natural gas solenoid valve (F) allows natural gas to pass from the regulator into the gas mixer or fuel injectors. The solenoid valve shuts off the natural gas when the engine is not running. Natural gas mixed with air flows down through the carburetor or fuel-injection system (G) and enters the engine combustion chambers where it is burned to produce power, just like gasoline.

Some heavy-duty vehicles use spark-ignited natural gas systems, but other systems exist as well. High-pressure direct injection engines burn natural gas in a compression-ignition (diesel) cycle.

What is Fischer-Tropsch diesel?

Fischer-Tropsch (F-T) diesel is synthetic diesel fuel produced by converting gaseous hydrocarbons, such as natural gas and gasified coal or biomass, into liquid fuel.

Fischer-Tropsch Diesel as an Alternative Fuel

Fischer-Tropsch diesel can be substituted directly for conventional (petroleum-derived) diesel to fuel diesel-powered vehicles, without modification to the vehicle engine or fueling infrastructure.

To enhance energy independence in the face of apartheid-related embargoes, South Africa satisfied most of its diesel demand with natural gas- and coal-derived F-T diesel for decades and is still using the fuel in significant quantities. More recently, global concerns about energy supplies and costs and the environment have created interest in F-T fuels elsewhere. For example, Shell markets F-T diesel as a premium diesel blend in Europe and Thailand. In the United States, F-T diesel has been used in demonstration projects.

What is a propane vehicle?

Propane, also known as liquefied petroleum gas (LPG), has been used in vehicles since the 1920s. It is considered an alternative fuel under the Energy Policy Act of 1992 and qualifies for alternative fuel vehicle tax incentives.

Today, most propane vehicles are conversions from gasoline vehicles. Dedicated propane vehicles are designed to run only on propane; bi-fuel propane vehicles have two separate fueling systems that enable the vehicle to use either propane or gasoline.

Propane vehicle power, acceleration, and cruising speed are similar to those of gasoline-powered vehicles. The driving range for bi-fuel vehicles is comparable to that of gasoline vehicles. The range of dedicated gas-injection propane vehicles is generally less than gasoline vehicles because of the 25% lower energy content of propane and lower efficiency of gas-injection propane fuel systems. Extra storage tanks can increase range, but the additional weight displaces payload capacity. Liquid Propane Injection engines, introduced in 2006, promise to deliver fuel economy more comparable to gasoline systems.

Lower maintenance costs are a prime reason behind propane's popularity for use in delivery trucks, taxis, and buses. Propane's high octane rating (104 to 112 compared with 87 to 92 for gasoline) and low carbon and oil contamination characteristics have resulted in documented engine life of up to two times that of gasoline engines. Because the fuel mixture (propane and air) is completely gaseous, cold start problems associated with liquid fuel are eliminated.

Compared with vehicles fueled with conventional diesel and gasoline, propane vehicles can produce significantly lower amounts of harmful emissions. Another benefit of propane vehicles is increasing U.S. energy security.

B20 and B100: Alternative Fuels

The interest in biodiesel as an alternative transportation fuel stems mainly from its renewable, domestic production; its safe, clean-burning properties; and its compatibility with existing diesel engines.

Biodiesel can be legally blended with petroleum diesel in any percentage. The percentages are designated as B20 for a blend containing 20% biodiesel and 80% petroleum diesel, B100 for 100% biodiesel, and so forth. B100 and blends of B20 or higher qualify for alternative fuel credits under the Energy Policy Act of 1992.

B20

Twenty percent biodiesel and 80% petroleum diesel—B20—is the most common biodiesel blend in the United States. Using B20 provides substantial benefits but avoids many of the cold-weather performance and material compatibility concerns associated with B100.

B20 can be used in nearly all diesel equipment and is compatible with most storage and distribution equipment. B20 and lower-level blends generally do not require engine modifications. Not all diesel engine manufacturers cover biodiesel use in their warranties, however. See the National Biodiesel Board's Standards and Warranties page to learn more about engine warranties. Because diesel engines are expensive, users should consult their vehicle and engine warranty statements before using biodiesel. It is similarly important to use biodiesel that meets prescribed quality standards—ASTM D6751-07b (see Biodiesel Production for more information on this standard).

Biodiesel contains about 8% less energy per gallon than petroleum diesel. For B20, this could mean a 1 to 2% difference, but most B20 users report no noticeable difference in performance or fuel economy. Greenhouse gas and air-quality benefits of biodiesel are roughly commensurate with the blend; B20 use provides about 20% of the benefit of B100 use and so forth. Low-level biodiesel blends also provide benefits.

B100

B100 or other high-level biodiesel blends can be used in some engines built since 1994 with biodiesel-compatible material for parts such as hoses and gaskets. However, as biodiesel blend levels increase significantly beyond B20, a number of concerns come into play. Users must be aware of lower energy content per gallon and potential issues with impact on engine warranties, low-temperature gelling, solvency/cleaning effect if regular diesel was previously used, and microbial contamination.

B100 use could also increase nitrogen oxides emissions, although it greatly reduces other toxic emissions. All these issues can be handled, but currently B100 use might be best for professional fleets with maintenance departments prepared to deal with this fuel.

What is Natural Gas?

Natural gas is a mixture of hydrocarbons, predominantly methane (CH4). As delivered through the pipeline system, it also contains hydrocarbons such as ethane and propane and other gases such as nitrogen, helium, carbon dioxide, hydrogen sulfide, and water vapor. See the AFDC Fuel Properties database for more details.

Natural gas has a high octane rating and excellent properties for spark-ignited internal combustion engines. It is non-toxic, non-corrosive, and non-carcinogenic. It presents no threat to soil, surface water, or groundwater.

Most natural gas is extracted from gas and oil wells. Much smaller amounts are derived from supplemental sources such as synthetic gas, landfill gas and other biogas resources, and coal-derived gas.

Natural gas accounts for approximately one quarter of the energy used in the United States. Of this, about one third goes to residential and commercial uses, one third to industrial uses, and one third to electric power production. Only about one tenth of one percent is currently used for transportation fuel.

What is ultra-low sulfur diesel?

Ultra-low sulfur diesel (ULSD) is diesel fuel with 15 parts per million (ppm) or lower sulfur content. The U.S. Environmental Protection Agency requires 80% of the highway diesel fuel refined in or imported into the United States (100% in California) to be ULSD as of 2006. One hundred percent must be ULSD nationwide by 2010. Different requirements apply to non-highway diesel.

Currently, the vast majority of ULSD is produced from petroleum. However, biodiesel; biomass-to-liquids, coal-to-liquids, and gas-to-liquids diesel; and hydrogenation-derived renewable diesel are inherently ultra-low sulfur fuels and could help meet ULSD requirements in the future. Petroleum-based ULSD is not considered an alternative fuel under the Energy Policy Act of 1992 (EPAct), but most ULSD fuels produced from non-petroleum and renewable sources are considered EPAct alternative fuels.

Ultra-Low Sulfur Diesel as a Vehicle Fuel

Ultra-low sulfur content in diesel fuel is beneficial because it enables use of advanced emission control technologies on light-duty and heavy-duty diesel vehicles. The combination of ULSD with advanced emission control technologies is sometimes called Clean Diesel.

Nitrogen oxides (NOx) and particulate matter (PM) are the two most harmful diesel pollutant emissions. These emissions can be controlled with the use of catalytic converters (for NOx) and particulate traps (for PM). However, sulfur—in amounts that used to be allowable in diesel fuel—deactivates these devices and nullifies their emissions control benefits. Using ULSD enables these devices to work properly.

In general, ULSD should cause no noticeable impact on vehicle performance, although fuel economy might be slightly reduced because the process that produces ULSD can also reduce the fuel's energy content. Removing sulfur from diesel reduces lubricity. This issue can be resolved by the addition of additives prior to retail sale that increase lubricity. In addition, blending biodiesel with ULSD also increases lubricity.

Using ULSD in older diesel vehicles might affect fuel system components or loosen deposits in fuel tanks. These vehicles should be monitored closely for fuel system problems and premature fuel filter plugging during the transition to ULSD. New vehicles designed to use ULSD must never be fueled with a higher-sulfur fuel. If kerosene is blended with ULSD for improved cold-weather performance, it must be ultra-low sulfur (15 ppm or lower) kerosene. New engine oils have been developed for use with new diesel vehicles fueled with ULSD.

What is hydrogen?

Hydrogen is the simplest and most abundant element in the universe—it is number 1 on the periodic table of elements (this link takes you to Los Alamos National Laboratory's site). At Earth surface temperatures and pressures, it is a colorless, odorless gas (H2). However, hydrogen is rarely found alone in nature. It is usually bonded with other elements. See the AFDC Fuel Properties database for more details.

Very little hydrogen gas is present in Earth's atmosphere. Hydrogen is locked up in enormous quantities in water (H2O), hydrocarbons (such as methane, CH4), and other organic matter. Efficiently producing hydrogen from these compounds is one of the challenges of using hydrogen as a fuel.

Currently, steam reforming of methane (natural gas) accounts for about 95% of the hydrogen produced in the United States. Almost all of the approximately 9 million tons of hydrogen produced here each year are used for refining petroleum, treating metals, producing fertilizer, and processing foods. Hydrogen has been used for space flight since the 1950s; learn more on the NASA Web site.

Hydrogen also can be used to fuel internal combustion engines and fuel cells, both of which can power low- or zero-emissions vehicles such as fuel cell vehicles. Major research and development efforts are aimed at making hydrogen vehicles practical for widespread use.

Diesel Vehicles

Diesel vehicles may be making a comeback. Diesel engines are more powerful and fuel-efficient than similar-sized gasoline engines (about 30-35% more fuel efficient). Plus, today's diesel vehicles are much improved over diesels of the past.

Better Performance

Improved fuel injection and electronic engine control technologies have

• Increased power
• Improved acceleration
• Increased efficiency

New engine designs, along with noise- and vibration-damping technologies, have made them quieter and smoother. Cold-weather starting has been improved also.

Cleaner

Today's diesels must meet the same emissions standards as gasoline vehicles, and advances in engine technologies, ultra-low sulfur diesel fuel, and improved exhaust treatment have made this possible.

Although emissions of particulates and smog-forming nitrogen oxides (NOx) are still relatively high, new "clean" diesel fuels, such as ultra-low sulfur diesel and biodiesel, and advances in emission control technologies will reduce these pollutants also.