So the government looked to enterprising teams to develop the technology for driverless vehicles, sweetening its offer with the two-million-dollar purse.

　　None of the 23 teams knows what lies ahead for this year's race. DARPA won't reveal the exact route until two hours before the start of the race on Saturday.

　　But the obstacles on the Fontana qualification course-including a steel—enforced tunnel that wipes out a vehicle's global positioning system—are made to resemble the rugged, real-life conditions that the vehicles will have to navigate.

　　The vehicles use sensors such as lasers, cameras, and radar to help them avoid obstacles such as rocks and cliffs. The computer's brain has to figure out how to resolve unexpected conflicts, like a boulder sitting in the middle of the road.

　　"Think about all the decisions that you and I have to make when we drive from our house to the store," Kurjanowicz said. "These vehicles have to do the same thing, without a driver."

　　Among the top contenders in Saturday's race is TerraMax, a massive truck originally built by the Wisconsin-based Oshkosh Truck Corporation for the U.S. Marine corps.

　　In last year's race, TerraMax managed to go only 1.2 miles (2 kilometers). Team leader Gary Schmiedel expects to do much better this year. He pointed to the new all-wheel steering feature on the truck as an important addition.

　　"We can move this large, 15-ton (13.5-metric ton) payload vehicle in a turn that's equivalent to that of a Humvee," he said.