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Diesel vs. hybrid: From Detroit to D.C., and back Gasoline prices that have been averaging more than $2 a gallon have boosted interest in fuel-efficient gas-electric hybrid and diesel-powered vehicles. To see if the technologies live up to their fuel-economy promise, USA TODAY reporter David Kiley drove a Volkswagen Jetta TDI diesel from suburban Detroit to suburban Washington, D.C., last month. He drove a Toyota Prius hybrid back from Washington to Detroit. Here's his report. Testing a diesel Jetta and hybrid Prius on a drive between Detroit and Washington seemed a natural. Volkswagen and Toyota each said I should be able to make the 500-mile-plus one-way trip on one tank of gas. Volkswagen's Jetta GLS 2.0, top, and Toyota Prius Volkswagen, Toyota The route seemed appropriate because decisions that determine the future of hybrids and diesels will be made largely in corporate Detroit and political Washington. The verdict: Prius is comfortable, a festival of technology and unquestionably cleaner-burning than the VW can be today with only high-sulfur diesel fuel available. But the real-world mileage of pleasant-driving Jetta was better than that of Prius, and diesel fuel typically was 16% to 20% cheaper than unleaded gas. Jetta lived up to its one-tank billing. Prius did not. The details: Setting out from my home in Ann Arbor, Mich., in the Jetta, I wanted to top off the tank. I went to three stations before finding diesel fuel. But that was the only time I had to hunt for it. FUEL ECONOMY Find official fuel economy figures for late model cars, SUVs, pickup trucks and minivans. The diesel pump was grimier than the others and offered plastic mittens for holding the nozzle. I skipped the mittens but didn't get dirty or smelly. The Jetta handled well, making the drive pleasant. Its diesel had more of a pulsating and vaguely clattering sound than the steady growl of a gas engine, but it wasn't objectionable. The odometer said 535 miles when I arrived at USA TODAY headquarters in McLean, Va. The Jetta used 12.2 gallons of diesel fuel. That's 44 miles a gallon, on the nose for the car's highway fuel economy rating. The fuel cost $21.35. The trip from McLean back to Ann Arbor in the Prius using a slightly different route was 549 miles. While in stop-and-go traffic, the Prius often ran on battery power, driving home the point that it is most efficient in crawling, urban traffic. The gas-tank warning light flashed after 422 miles. I drove 10 miles to the next gas station and filled up, putting 11.1 gallons into the 11.9-gallon tank. That would indicate 38 mpg, far short of the 51 mpg government rating. The car's trip computer told me it had been getting 51.7 mpg. Irv Miller, Toyota vice president for corporate communication, says the mileage shortfall probably had to do with speed. "The government test that puts the Prius' highway mileage at 51 mpg is based on ideal driving conditions and going 55 mph," he says. I averaged 72 miles an hour on highways. The company also says the computer is nearly 100% accurate. But how much gas its flexible bladder takes at the pump varies from less than 10 gallons to the full 11.9 gallons. Toyota said I probably began the trip with less gas than I thought. Toyota spokesman Mike Michels says the gas-tank variability is confusing to owners, and the company is working on a fix. Possibly reflecting frustration with the problem, Prius owners' biggest complaint was "fuel gauge not working" in the J.D. Power and Associates 2004 Initial Quality Study, which measures problems the first 90 days of ownership. Gas bill for the trip home was $28.62. While the fuel price advantage on this trip goes to the diesel, the environmental advantage goes to the hybrid. The Jetta spews out six times more sulfur particulates than Prius, which can run almost emission-free when using low-sulfur gasoline available in California but almost nowhere else. Federal regulations require phasing in of low-sulfur gas and diesel the next few years, which will improve the emission performance of both gas and diesel vehicles. The advantage in premium paid for the technology goes to diesel. The premium for a hybrid version of a vehicle is about $3,000. The Jetta diesel is $1,200 more than a gas-powered Jetta. VW's Passat TDI diesel, which just went on sale, is only $205 more than the similar gas model. And the VW Touareg TDI diesel, also just now on sale, is priced about the same as a similarly accessory-laden gasoline V-8. The future: Both technologies are in demand. Toyota can't keep up on Prius. Some dealers won't take more 2004 orders until production is increased, although Toyota discourages that, Michels says. Toyota plans to make 48,000 to 50,000 a year available in the USA, up from 36,000 now. Ford Motor, which launches a hybrid version of the Ford Escape small sport-utility vehicle in August, said recently it had 30,000 potential customers for what is expected to be production of 20,000. Ford is investigating whether it can get enough batteries to build more than that. Meanwhile, VW says it gets a limited number of diesels from Germany and sells all the TDI vehicles it has. More hybrids and diesels are coming. In addition to Civic and Insight hybrids, Honda will sell an Accord hybrid in the fall. Toyota's Lexus luxury brand will offer an RX 400h SUV later this year, and Toyota will have a hybrid version of Highlander SUV early next year. Mercedes-Benz has brought its E Class diesel back to the USA. Chrysler plans a Jeep Liberty diesel later this year.