Diesels versus hybrids: comparing the environmental costs.

• Author: Kester, Corinna

High fuel prices and concerns about climate change are boosting the popularity of gasoline/electric hybrid cars in the United States and abroad. However, environmentally minded motorists have another choice--diesels--which account for 45 percent of new passenger-car sales in European markets. Besides fuel economy concerns, the reasons include lower taxes on diesel fuel and greater tolerance of higher air emissions. Enthusiasm for diesels is relatively muted in the United States, with sales of approximately 30,000 diesels per year, mostly Volkswagens. Compare this to the sales of hybrid cars: more than 180,000 have been sold in the United States to date, 85,000 of them in the last year.

Americans generally think diesels are noisy, dirty, and underperforming. In a 2002 diesel vehicle survey by J.D. Power and Associates, 32 percent of Americans were concerned about engine noise, 27 percent about exhaust odor, and 31 percent about lower performance. However, these concerns are largely misplaced; most Americans remember the dirty diesels of decades past and are not aware of the advances incorporated into modern diesel vehicles. For example, in the last 15 years, diesel engines have reduced noise by 60 percent, emissions by 90 percent, and fuel consumption by 30 percent, while increasing torque by 100 percent. Modern diesels can be as desirable to consumers as gasoline automobiles, but how does their environmental performance measure up?

To answer this question, we must examine the entire lifecycle of the vehicle, including extracting raw materials, manufacturing and assembling automobile components, producing and combusting fuel, and maintaining and disposing of vehicles. Several differences between diesels and hybrids are undeniable: diesel engines are inherently more efficient than gasoline engines, diesel fuel contains approximately 10 percent more energy per volume than gasoline, and diesels produce significantly more air pollution. A closer look at the models offered today highlights these differences.

Three hybrid and three diesel passenger cars are currently offered in the United States (excluding the two-passenger Honda Insight and the luxury Mercedes-Benz E320 CDI). Table 1 provides basic size, weight, price, and performance data for these cars. The Honda Accord is the most expensive and the best performing; the other cars closely match each other in cost and performance. Overall, the diesel vehicles have a smaller cost differential...