In the race to develop driverless cars, several automakers and technology companies are already testing vehicles that pilot themselves on public roads. And others have outlined plans to expand their development fleets over the next few years.

But few have gone so far as to give a definitive date for the commercial debut of these cars of the future.

Now Ford Motor has done just that.

At a news conference on Tuesday at the company’s research center in Palo Alto, Calif., Mark Fields, Ford’s chief executive, said the company planned to mass produce driverless cars and have them in commercial operation in a ride-hailing service by 2021.

Beyond that, Mr. Fields’s announcement was short on specifics. But he said that the vehicles Ford envisioned would be radically different from those that populate American roads now.