With gasoline prices rocketing and the fuel-economy debate heating up, General Motors Corp. is renewing a push to relax clean-air standards to allow the sale of more diesel-powered passenger cars and trucks, according to a May 21 story by Jeff Plungis in the Detroit News. GM and other automakers are embracing diesel as they face increasing pressure to improve the fuel economy of their vehicle fleets. Diesel burns 30 percent more efficiently than gasoline, but gives off more soot and smog-producing emissions. While diesel-powered vehicles have never been very popular in the United States, their use is growing rapidly in Europe and Japan where high fuel prices make fuel-economy a higher priority than stringent clean-air rules. Attempts to expand the use of diesel in the American market are likely to be met with skepticism from consumers and stiff resistance among environmental groups and health advocates, according to industry analysts. Diesel technology has undeniably advanced in recent years. While diesels sold in the 1980s were noisy, sluggish and dirty, today's diesels are much improved, with lower emissions and perky but quiet performance. Nationwide, a gallon of diesel fuel now costs $1.49, while a gallon of regular unleaded gasoline sells for $1.71. The automakers have a big financial stake in diesels. GM and Ford Motor Co. have spent billions of dollars in recent years developing cleaner diesels for foreign markets. They also are developing diesel engines for commercial trucks. The biggest hurdle to the introduction of powerful, fuel-efficient diesels are new tailpipe emissions rules that take effect in 2004. The U.S. Environmental Protection Agency (EPA) rules reduce the amount of harmful emissions vehicles can emit while requiring them to burn cleaner fuels with less sulfur. But the automakers argue that the rules are too strict in respect to diesel, which could help them increase the fuel-economy of their new vehicle fleets. The biggest gains could be for sport utility vehicles and pickup trucks. Under EPA regulations, an automaker's fleet of cars and trucks, considered as a whole, can only emit a certain amount of nitrous oxide (NOx). A manufacturer may sell more-polluting vehicles if those sales are offset by more cleaner-burning vehicles. Automakers believe the restrictions will limit their ability to sell diesel-powered sport-utility vehicles and pickups, a high-profit segment of the market that would benefit the most from higher-mileage, more powerful diesel engines. Volkswagen AG is the only manufacturer that sells passenger vehicles equipped with diesel engines in the United States. The diesel-powered Beetle, Golf and Jetta now account for 10 percent of each models' annual U.S. sales. The vehicles get 49 miles per gallon on the highway and 42 mpg in the city, compared with 31 mpg and 24 mpg for their gasoline counterparts. Attempts to revise EPA rules would rekindle years of debate about the health benefits and costs of emissions regulations, according to industry analysts. Because diesel engines emit more NOx and soot environmental and health groups fear relaxed rules would mean more cases of asthma and lung disease. There are also concerns that diesel exhaust may cause cancer. The Union of Concerned Scientists estimates that a diesel car would emit between 16 and 20 times more particulate matter than an equivalent gasoline-powered car. Automakers eager to ease restriction on diesel face an uphill battle with environmentalists, including California regulators, who have adopted much stricter air quality standards. The California Air Resources Board prohibits the sale of higher-polluting vehicles permitted by federal regulations, essentially precluding the sale of light-duty diesel vehicles in California. In 1998, the state labeled diesel exhaust a toxic air contaminant. VW is limited to 3,000 diesel vehicles sales a year in California. In unveiling the new emissions rules in December 1999, the Clinton administration projected the costs of the regulations would add less than $100 to the price of a new car, less than $200 for a new light-duty truck, and just two cents per gallon of gas. The EPA says benefits outweigh projected costs by as much as five-to-one. The EPA estimated that by 2030, the regulations would prevent 4,300 premature deaths and 10,200 cases of bronchitis each year; 260,000 asthma attacks, and 173,000 cases of respiratory illness, among children each year. The agency also projected the regulations would save 683,000 missed workdays and over 5 million days of restricted activity due to acute respiratory symptoms each year.