UCS research shows diesel has improved, but still has a long way to go. Here's what new car buyers need to know.
By Patricia Monahan and David Friedman
Over the past few years, diesel's popularity as an automotive fuel has grown significantly. Thanks to its higher energy content and efficient combustion process, diesel enables cars to travel at least 30 percent farther on a gallon of fuel than comparable gasoline models. As a result, diesel engines generally release less carbon dioxide—the heat-tapping gas primarily responsible for global warming—from the tailpipe. The improved efficiency of diesel engines can also help reduce oil consumption.
But diesel is no silver bullet. When it comes to smog-forming pollutants and toxic particulate matter (soot), today's diesels are a lot dirtier than the average gasoline car. They're also pricier.
Technologies are being developed that can make diesel much cleaner and more fuel-efficient. So, which automotive choice is best to reduce oil usage, global warming pollution, and toxic air contaminants-and save money at the pump? The new UCS report, The Diesel Dilemma: Diesel's Role in the Race for Clean Cars, seeks to answer this question by comparing the cost, fuel economy, and emissions performance of conventional, advanced, and hybrid-electric diesel and gasoline cars.
Our analysis provides an "apples-to-apples" comparison by evaluating vehicles with equivalent 0 to 60 mph acceleration performance, assuming both fuels can achieve the same emission levels under federal tailpipe standards and accounting for energy content differences in the fuels. We also analyzed various fuel-saving technologies such as more efficient engines, improved transmissions, better aerodynamics, and hybridization.
On the Road to Reform
If you or your parents owned a diesel car 20 years ago, you may have some bad memories of the experience. American drivers have steered clear of diesel since the early 1980s because many of the cars were unreliable, noisy, and polluting. Today's diesel cars have overcome most of their past performance problems, but they still accounted for less than three percent of all new U.S. automobile and truck sales in 2001. In Europe, on the other hand, about 40 percent of new cars sold are diesel, amounting to more than five million vehicles each year. The demand for diesel in Europe is fueled by the high cost of gasoline (unequal taxation of the two fuels results in diesel costing about one dollar less per gallon in most European countries).
Diesel Economics Improved vehicle technology can cut oil usage and global warming pollution by more than 50 percent while saving consumers money. Our modeling, though, suggests that the high up-front cost of diesel engines and emission controls gives gasoline technology the edge in cost-effectiveness.
Based on the fuel formulations used in our report, a 30 percent reduction in oil demand and heat-trapping emissions adds between $2,600 and $2,800 to the average diesel passenger vehicle's sticker price, while a 50 percent reduction adds $4,300 to $4,800. These costs are $1,100 to $1,800 higher than equivalent gasoline vehicles.
The higher up-front costs of efficient diesel and gasoline vehicles are more than offset by lower fuel costs, resulting in a net savings of $400 to $2,000 over a vehicle's useful life. Gasoline vehicles, however, offer a higher net savings than diesel-as much as $700 for an equivalent improvement in fuel efficiency.
It should be noted that different gasoline and diesel formulations can affect cost, oil demand, and heat-trapping emissions. Nevertheless, our general finding that diesel is not more cost-effective than gasoline appears to hold true among common gasoline and diesel formulations. |
Americans continue to perceive diesel as a "dirty" fuel. Although this image can change as a result of new technology, questions remain about just how much cleaner diesel vehicles can get. For example, U.S. tailpipe standards for diesel cars, which have historically been weaker than those for gasoline cars, are being updated to force diesel and gasoline vehicles to meet the same set of emissions standards. The tiered structure of the new "Tier 2" standards, however, allows automakers to produce some cars that release two times more soot and smog-forming pollution than the average new vehicle and still meet their targets. Also, until the standards are fully implemented in 2009, existing loopholes allow some cars to pollute even more.
To meet the Tier 2 standards, low-sulfur diesel fuel will be required by federal law starting in mid-2006. Unfortunately, Department of Energy modeling shows this fuel to be more oil- and carbon-intensive than reformulated gasoline. Each gallon, for example, requires 25 percent more oil and emits 17 percent more heat-trapping gases than gasoline reformulated with MTBE (the formulation used in our report), and requires 17 percent more oil and emits 18 percent more heat-trapping gases than gasoline reformulated with ethanol. So, although diesel's higher energy content, along with efficient engines, allows cars meeting the Tier 2 standards to travel 30 to 40 percent farther than gasoline models, these fuel economy improvements do not provide equivalent reductions in oil use and heat-trapping emissions.
Getting the Most Out of Diesel
Future diesel vehicles, though perhaps not as cost-effective as gasoline, may have a role to play in reducing oil consumption and global warming pollution. Of the vehicles we evaluated, full hybrid-electric diesels offered the maximum improvement in fuel economy as well as the greatest reduction in heat-trapping emissions. But a key challenge remaining is whether diesel vehicles will ever be able to deliver the progress on air pollution that efficient modern gasoline technology can achieve today.
This may be possible if we adopt smart public policies that link public health and environmental goals and treat diesel and gasoline similarly. UCS proposes that federal, state, and local governments take the following actions to achieve these goals:
Maintain Tier 2 standards. The federal government needs to fully implement the new emissions standards and prevent any attempts to weaken them. Researchers also need to monitor vehicles' real-world pollution performance and study the public health effects of non-regulated emissions (to determine whether the federal standards are effective).
Inspection and maintenance programs, which can help reduce the gap between expected and real-world pollution, should be expanded to include diesel vehicles, particularly if diesel becomes more popular in the light-duty vehicle sector.
Adjust Corporate Average Fuel Economy (CAFE) standards. CAFE standards give credit to vehicles based on fuel economy rather than oil use. Since diesel fuel requires more oil per gallon than reformulated gasoline, putting more diesel vehicles on the road could actually increase U.S. oil dependence. To eliminate any unfair advantages, CAFE standards should, at a minimum, compare gasoline and diesel on an energy-equivalent basis.
Offer incentives for clean cars. Protecting public health and improving vehicle fuel economy can and must be complementary goals. Incentives for vehicles with higher fuel economy and lower pollution—regardless of fuel type—can help increase production volume, lower costs, and raise consumer awareness of new vehicle technologies.
Improve vehicle labels for consumers. The window sticker on new vehicles does not give consumers enough information to evaluate the air quality, global warming, and energy security implications of their purchase. The Environmental Protection Agency should require better labeling to help consumers make smarter choices. In the interim, consumers should at least look for a vehicle certified to the Tier 2 Bin 5 standard, though cleaner gasoline and hybrid-electric vehicles are available.
Our nation needs to reverse a two-decade trend of falling fuel economy and rising oil imports. Our analysis suggests this—and more—is possible. With improved technologies and policies in place, we could reduce our oil consumption, protect public health, and reduce heat-trapping emissions—all at the same time.
Patricia Monahan is a senior analyst and David Friedman is research director for the Clean Vehicles Program.
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