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Even though the idea of driverless vehicles sparks flights of the imagination, don't expect a fully autonomous car to be on the market anytime soon, researchers say.

Autonomous vehicles for military applications are probably five to 10 years away, performing tasks such as removing mines and explosive devices. It will be 20 years before a fully autonomous car hits the mainstream market, according to Sebastian Thrun, project leader of the Stanford Racing Team.

For one thing, the cost will have to come down. Experimental cars have run the gamut in price. The AnnieWAY, developed by a German team led by Palo Altan Annie Lien, cost $300,000. Junior, Stanford's current prototype, cost $2 million -- four times that of the team's first robotic car, Stanley, Thrun said.

And there are greater obstacles beyond technology.

"There are all the [transportation-safety] regulation hurdles. Who will be responsible if it crashes? If you don't have a driver anymore, the liability shifts to the manufacturer," he said.

Even if fully autonomous cars may not materialize soon, commercial applications will come in stages in the form of driver-assistance devices, such as lane tracking that senses when fatigued drivers are drifting off roads, according to Thrun.

Such applications could be hugely effective in reducing fatalities -- something that has touched Thrun personally. He has known several people who died in traffic crashes.

And when he lectures, he often asks audience members how many of them have known someone who died in an auto accident.

"Half the audience raises a hand," he said.

There is no question in some researchers' minds that autonomous cars, whenever they become mainstream, will lead to greater safety on increasingly dangerous roads.

With virtually no new highway construction in the state and a 3-percent increase of highway traffic per year, Thrun said crowded highways could lead to disastrous conditions.

He envisions a future that could leverage the existing space and increase fuel economy by as much as 17 percent by close convoying of trucks. And because of their accuracy, robotic trucks could travel successfully at such close tolerances without having accidents. In tests, some computer-driven trucks have an accuracy of driving 10 centimeters apart at 70 mph, he added.

"Eight percent of the gap is taken up by the car. The rest is completely free space. It's because we are lousy drivers," he said.

— Sue Dremann