The Diesel Dilemma (2004)

April 2005
Diesel is becoming cleaner, but gasoline vehicles are more cost-effective than diesel for reducing oil use and lowering global warming pollution.

This is excerpted from the executive summary of the UCS report, The Diesel Dilemma: Diesel's Role in the Race for Clean Cars, January 2004.

Increasing concerns over oil dependence and climate change have prompted renewed U.S. interest in diesel technology for cars and trucks despite a history of poor sales in the American market. Diesel also continues to carry the stigma of being a “dirty” fuel. This image has the potential to change as a result of new technology, but questions remain about how much cleaner diesel vehicles can get.

If emissions challenges can be overcome, diesel cars may be able to incorporate and compete with other fuel-saving technologies, such as more efficient engines, better transmissions, improved aerodynamics, and high-strength materials. Diesels may still carry a higher price tag, however. 

 Should Americans invest in diesel or gasoline cars and light trucks to reduce oil usage, global warming pollution, and toxic air contaminants--while saving money at the pump? The Diesel Dilemma: Diesel’s Role in the Race for Clean Cars explores this question by comparing the cost, fuel economy, and emissions performance of conventional, advanced, and hybrid-electric diesel and gasoline cars.

This report presents a new “apples-to-apples” comparison of diesel and gasoline technologies, applying each to the five major classes of passenger vehicles (small cars, larger “family” cars, sport utility vehicles, minivans, and pickup trucks).

Major Findings & Recommendations

Diesel is becoming much cleaner, but key questions and challenges remain.
Diesel vehicles appear to be on track to meet the average federal emissions standards. However, concerns about real-world emissions, long-term pollution reduction, and the importance of nonregulated emissions may create public health barriers and cloud diesel’s future.

Gasoline vehicles are more cost-effective than diesel for reducing oil use and lowering global warming pollution.
As shown in Table ES-1, more efficient gasoline and diesel vehicles could substantially improve fuel economy and save consumers money at the pump. Our modeling, though, suggests that the high up-front cost of diesel engines and emission controls allows improved gasoline vehicles to deliver energy security and global warming benefits at a lower cost.

Table ES-1: Comparing Gasoline & Diesel Vehicles at a Glancea

 Diesel

 Gasoline

Initial cost

-

o

Net consumer savings

+

++

Cost-effectiveness for oil reduction

+

++

Cost-effectiveness for global warming benefits

+

++

Infrastructure availability

-

++

Tested tailpipe pollution

-

+

In-use pollutionb

 --?

-

Extreme towing capability

+

 
Range

+

o

Maximum potential oil reduction

+

+

Maximum potential global warming benefitsc

++?

+

KEY
"+" This vehicle type excels in this area.
"-" This vehicle type performs poorly in this area.
"o" This vehicle type performs adequately in this area.
NOTES
a. Multiple marks indicate significantly superior or inferior performance.
b. Assuming diesel emission controls fall at the same rate as gasoline, resulting in higher in-use pollution.
c. If diesel soot proves to be an important heat-trapping gas and is difficult to control, the potential global warming benefits from diesel will be muted.

Regulatory standards should focus on protecting public health.
At a minimum, the federal government must refrain from weakening its new Tier 2 tailpipe emissions standards. These standards are expected to prevent as many as 4,300 deaths per year (EPA, 1999) and should not be compromised. In addition, research is needed on the impact of particle size, number, and toxicity to determine whether Tier 2 standards protect human health sufficiently.

Make fuel economy standards truly “fuel neutral.”
Since Corporate Average Fuel Economy (CAFE) standards give credit to vehicles based on fuel economy rather than oil use, and a gallon of low-sulfur diesel fuel requires 25 percent more oil than a gallon of low-sulfur reformulated gasoline, putting more diesel vehicles on the road without also raising fuel economy standards could actually increase U.S. oil dependence. CAFE standards should, at a minimum, compare gasoline and diesel on an energy-equivalent basis.

Government incentives should focus on economy/ emissions performance, not on technology type.
The United States should not follow Europe’s lead by giving diesel tax advantages over gasoline or by creating new emissions loopholes. Performance-based incentives that focus on conventional technology can include diesel engines, but must also provide the same benefits to other conventional vehicle technologies and must reward higher fuel economy or lower heat-trapping gas emissions while also requiring lower tailpipe emissions than the average new car. Additional support for hybrid vehicles is merited given their link to a potential clean hydrogen fuel cell vehicle future. 

Consumers should compare diesel and gasoline carefully.
Today’s new vehicle window sticker does not give consumers enough information to evaluate the air quality, global warming, and energy security implications of investing in a diesel or gasoline car. Until the EPA mandates better labels, consumers should consider diesel vehicles that dealers can confirm are certified to the federal Tier 2 Bin 5 standard, though consumers should also be aware that cleaner gasoline and hybrid electric vehicles are available today. When evaluating a diesel vehicle’s impact on oil dependence, consumers should adjust the listed fuel economy downward about 20 percent before comparing it with a gasoline vehicle.

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