Twenty-three Audi vehicles were driven from New York to California to prove a point: clean-diesel engine technology can deliver both power and fuel economy. The point was proven. As one of the journalists driving the Audi A4 Michelin-sponsored sedan for the third leg (Denver to Las Vegas) of the cross-country trek, the car finished with an average mpg of 36.7. The Michelin-sponsored A4 in wave three packed on nearly 1,100 miles through mountainous terrain in Colorado, Navajo Indian Reservation desert land, and an oh-my-gosh canyon drive in Arizona on a full moon evening where speeds dipped as low as 15 mph to handle the severe switchbacks. In contrast, the A4 sedan, riding on Michelin Primacy HP tires, quickly and smoothly roared past 100 mph on occasion. The best A4 mileage (39 mpg) tallied during wave three’s drive was the stretch from Durango, Colorado to Sedona, Arizona. The Audi Mileage Marathon featured four models: the Q7, the Q5, the A3 and the A4. All but the A3 used the new 3.0-liter, V6 turbocharged TDI diesel engine. (The A3 had a 2.0-liter four-cylinder turbocharged TDI diesel engine.) Consumers can buy the first clean diesel vehicle (the Q7) in the 2009 model year. The clean diesel-powered A3 will follow, but the automaker hasn’t made an absolute determination about offering other clean diesel models (i.e. A4 and Q5). Audi’s new clean diesel engine meets the world’s most stringent emissions standard (California’s LEV II BIN 5). All fuel stops were at Shell stations and were handled by IMSA, the race sanctioning organization for the American LeMans Series. (IMSA officials signed a decal that was affixed to the fuel door after each scheduled fuel stop to prevent any chance of unauthorized fuel stops along the route.) Average mileage and average vehicle speeds were confirmed via onboard computer data acquisition systems.