The U.S. government has a message for the scores of companies racing to develop self-driving cars: We want to make your life easier.

U.S. Secretary of Transportation Elaine Chao on Tuesday unveiled revised federal guidelines for testing and deploying autonomous cars that aim to be nimble and supportive of innovation, while aligning with legislation currently pending in Congress, she said. The guidelines also clarify that states should play a limited role to avoid a messy patchwork of conflicting regulations.

“Our country is on the verge of one of the most exciting and important innovations in transportation history,” Chao said at an event at a 32-acre testing ground for autonomous vehicles at the University of Michigan in Ann Arbor. She ticked off benefits of robot cars: reducing traffic-accident fatalities and injuries; reclaiming time wasted in traffic jams; and providing new mobility for disabled and elderly people.

The framework from the Dept. of Transportation and National Highway Traffic Safety Administration, called A Vision for Safety 2.0, streamlines Obama administration guidelines released last year. “It’s not a static document,” Chao said, nothing that her department is already working on Version 3.0, due out next year.

The document clarifies that it is entirely voluntary for automakers to provide self assessments of their vehicles’ safety, but it encourages them to do so to win public trust.

Some consumer advocates said the policy placed too much trust in carmakers.

“This isn’t a vision for safety,” said John Simpson, privacy project director at Consumer Watchdog. “It’s a roadmap that allows manufacturers to do whatever they want, wherever and whenever they want, turning our roads into private laboratories for robot cars with no regard for our safety.”

Some traditional carmakers reportedly had lobbies for their self-driving vehicles to get preferential treatment over those developed by technology companies such as Alphabet’s Waymo and Apple. The guidelines emphasized that both types of companies should enjoy a level playing field.

“This new policy adjusts the tone but continues much of the substance of last year’s document,” said Bryant Walker Smith, an assistant professor of law at the University of South Carolina. “It clearly reflects the input of the traditional automotive industry but doesn’t exclude potential new entrants such as Waymo.”

The House this month passed a bill called the SELF DRIVE Act (an acronym for Safely Ensuring Lives Future Deployment and Research In Vehicle Evolution), and the Senate is now holding hearings on an equivalent bill. That federal legislation would play a stronger role than the transportation department guidelines, and more importantly, would supersede state regulations.

“It would be 100 percent unworkable to have different states with divergent laws for an inherently interstate activity like driving,” said Elliot Katz, a partner at law firm McGuire Woods and chair of its Connected & Automated Vehicle Group.

Carolyn Said is a San Francisco Chronicle staff writer. Email: [email protected] Twitter: @csaid