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  Even as Google plans to test its fleet（车队）of self-driving cars on public roads this summer, its business model remains a bit of a mystery. By 2025, as many as 250,000 self-driving vehicles could be sold each year globally, according to a study by an industry research firm.

"Vehicles that can take anyone from A to B at the push of a button could transform mobility for millions of people," said Chris Urmson, director of Google's self-driving car project. For now, Google has no plans to sell any of its self-driving cars. They are strictly for research. But they will hit public roads this summer near Google's headquarters in Mountain View, California. Previous testing has taken place only on closed courses.

The cars are built to operate without a steering wheel, accelerator（油门）or brake pedal. "Our software and sensors do all the work," Urmson said. "The vehicles will be very basic—we want to learn from them and adapt them as quickly as possible—but they will take you where you want to go at the push of a button." The prototype（雏形）are the first of a 100-car fleet the tech giant is building.

In the long run, Urmson sees a future of safer roads—the majority of auto accidents are caused by human error—and fewer traffic jams. Robotic cars could also shuttle people who can't drive because of age or illness.

Google has said that self-driving cars could launch new business models in which people buy the use of vehicles they don't own. The company has already tested other types of self-driving cars on public streets, including modified Lexus sport-utility vehicles, under a special permit program by the California Department of Motor Vehicles that requires a human driver at the controls.

The state has issued six other companies permits to operate such cars, including Delphi, Mercedes-Benz, Volkswagen, Tesla, Bosch and Nissan. The vehicles that will be tested on open roads this summer will have removable steering wheels, accelerators and brake pedals to allow "safety drivers" to take control if needed.

Google says the cars are safe. The vehicles have sensors that "can detect objects out to a distance of more than two football fields in all directions, which is especially helpful on busy streets with lots of intersections," Urmson said. "We're looking forward to learning how the community understands and interacts with the vehicles, and to uncovering challenges that are unique to a fully self-driving vehicle," Urmson said.