Josh Miller/CNET

Tesla Motors plans to roll out autonomous-driving software for its Model S sedan within the next three months, the company's chief executive, Elon Musk, said in a press conference Thursday.

Though not full-blown self-driving software, the over-the-air update will initially provide an automatic-steering capability that will let drivers travel hands-free and allow the car to move without a driver. Tesla has been testing the feature on a route from San Francisco to Seattle, "without the driver touching any controls at all," Musk said.

"It is technically capable of going from parking lot to parking lot. But we won't be enabling that [specific capability] for users with this hardware suite, because we don't think it's likely to be safe in suburban neighborhoods," Musk added. For now, Tesla pictures the ability to call your car with a tap on your smartphone or letting your Model S come in and out of a garage on its own.

Self-driving cars are a hot topic in Silicon Valley and the automotive industry. Search giant Google has developed software that it says can direct vehicles through any traffic environment without collisions. And many car companies, including BMW, Mercedes-Benz and Nissan, are working on autonomous-vehicle systems of their own. Tesla could have a competitive edge because of its ability to add features and functions across all its vehicles via software updates.

Without federal standards, self-driving car systems designed for the open road are currently restricted to testing and only with vehicles from auto makers licensed to do so. Musk advised Tesla owners that, at first, the Model S's autonomous features may only be useable on their personal property. He also drew a line between what Tesla is doing for the immediate future, and what companies like Google are attempting to achieve far down the line.

"There's certainly an expectation that when autopilot on the Model S is enabled, that you're paying attention," he said, so no falling asleep at the wheel. "But it should also take care of you if you have moments of distraction."

Speaking Tuesday at Nvidia's annual GPU Technology Conference in San Jose, Calif., Musk said the move to self-driving cars is inevitable, although it could take up to 20 years to replace the fleet of 2 billion cars on the road today at the current rate of 100 million new cars a year.

"It's not going to all transition immediately," he told Nvidia CEO Jen-Hsen Huang during an on-stage interview Tuesday. "It's going to take a while."

Musk also gave a warning to those who love to drive: Autonomous cars may become so much safer than people that it's possible human drivers could one day be outlawed.