Self-driving cars won't dominate American roadways for decades given millions of older vehicles consumers own, the top U.S. federal highway safety regulator said.
Traditional auto makers, suppliers and Silicon Valley giants and startups alike are racing to develop autonomous vehicles. But there are roughly 250 million cars and trucks currently on U.S. roadways that are more than a decade old on average, highlighting potentially long lead times before vehicles that predominantly drive themselves proliferate, Mark Rosekind, head of the National Highway Traffic Safety Administration, said Tuesday.
"For the next 20 to 30 years at least, we will likely have a mixed fleet of different levels of automation," Mr. Rosekind said before a House Energy and Commerce subcommittee. Ubiquitous fully self-driving cars "are years off," he said.
Auto makers are already deploying semiautonomous technologies that allow cars to perform driving functions themselves under limited circumstances, including automatic emergency brakes and adaptive cruise control that changes speeds based on traffic patterns.
Autonomous vehicles that don't require human intervention remain in testing stages, with companies eyeing ride-sharing fleets as initial laboratories for rolling them out to consumers. Uber Technologies Inc. earlier this year began letting some consumers hail autonomous taxis manned by backup drivers and engineers in the front seat to ensure safety.
Companies and government officials contend the technologies promise to improve safety and reduce rising traffic deaths. More than 90% of crashes can be tied to human choices or errors such as drunken driving or sending text messages from smartphones while behind the wheel, Mr. Rosekind said.
But the technologies are also drawing increased scrutiny. Mr. Rosekind's agency in June started probing Tesla Motors Inc.'s Autopilot system after a fatal crash involving one of the company's electric cars. Lawmakers didn't question Mr. Rosekind about the investigation. Tesla has since updated Autopilot with technology that Chief Executive Elon Musk claimed likely would have prevented the fatal crash.
Mr. Rosekind said regulators expect auto makers to comply with voluntary self-driving car guidelines that ask them to submit a 15-point safety assessment letter that includes details on how autonomous vehicles are tested, safeguards should systems fail and plans to prevent vehicle hacking. Regulators have so far avoided developing full-force regulations amid concerns a lengthy rule making process will fail to keep pace with rapid technological advances.
Auto makers are seeking more clarity on the safety assessment and are concerned about regulators' suggestions to collect and share companies' data.
"If you want everyone to trust what you're working on...we would think you want the most thorough, transparent public notice of what you're doing to address safety upfront," Mr. Rosekind said.
He added it remains "one of our biggest fears, frankly," that auto makers might take advantage of the guidelines' voluntary nature. "It's not required at this point, it's a policy," Mr. Rosekind said, though regulators are weighing future regulations that would compel the safety assessment.
Mr. Rosekind said maintaining driverless-car technologies could need government oversight. Asked whether they would be examined as part of traditional state safety inspections, Mr. Rosekind cited rupture-prone Takata Corp. air bags that became more dangerous over time and prolonged exposure to heat and humidity. Automated-driving sensors, radars and cameras "have a service life," Mr. Rosekind said. "How they will be maintained remains an open question in this coming period."