Google is building a car without a steering wheel that will drive itself.
The two-seater will not be sold publicly but Google said it hopes that, by this time next year, 100 prototypes will be on public roads. The top speed will be 25mph.
The cars are a natural next step for Google, which has driven hundreds of thousands of miles in California with Lexus SUVs and Toyota Priuses fitted with a combination of sensors and computers.
Those cars have Google-employed "safety drivers" behind the wheel in case of emergency. The new cars would eliminate the driver.
They will have no steering wheel, no brake and no accelerator pedals - just buttons for go and stop.
Sergey Brin, co-founder of Google, told a Southern California audience of his first ride: "It reminded me of catching a chairlift by yourself, a bit of solitude I found really enjoyable."
The electric-powered car is compact and bubble-shaped - something that might move people around a corporate campus or congested town centre.
Google is unlikely to go deeply into car manufacturing. Unveiling the prototype, the company emphasised partnering with other firms.
The biggest obstacle could be the law.
Test versions will have a wheel and pedals, because they must under California regulations.
Google hopes to build the 100 prototypes and use them in a "pilot programme". By the end of this year, California's Department of Motor Vehicles (DMV) must write regulations for the operational use of driverless cars.
The DMV had thought that reality was several years away, so it would have time to perfect the rules.
Head of the DMV's driverless car programme Bernard Soriano said: "Because of what is potentially out there soon, we need to make sure that the regulations are in place that would keep the public safe but would not impede progress."