The National Highway Traffic Safety Administration (NHTSA), an agency of Foxx's department, has called on automakers to voluntarily submit details of self-driving vehicle systems to regulators in a 15 point "safety assessment" and urged states to defer to the federal government on most vehicle regulations.

Some advocacy groups have called on Foxx's department to take tougher action to control autonomous vehicle development, enacting binding regulations. "I strongly believe we'll get great compliance from the auto industry," Foxx told Reuters in an interview at the department's Washington headquarters last week.

Foxx said establishing voluntary guidelines now gives regulators a framework for when automakers or technology companies start pushing to get self-driving cars on the road.

"Had we not done this there would have been a day, be it a year or two or four or five from now, when a manufacturer would have come to us with an autonomous car and we would have run it through the same algorithms ... we would run a conventional car through," Foxx said.

One goal, Foxx said, was to be less prescriptive than regulators typically are and give companies more flexibility in addressing the 15 areas. Automakers and others have two months to comment on the guidelines before they take effect.

NHTSA Administrator Mark Rosekind said in a C-SPAN interview broadcast Saturday that recent major auto safety regulations have taken six to 10 years to finalize. Self-driving cars are changing so fast, he said, that regulations "would be outdated before you ever got your regulation out."

In a boost for the guidelines, California's Department of Motor Vehicles Friday proposed revised draft requirements for autonomous vehicle testing that would require automakers to comply with NHTSA guidelines in order to test in California.

NHTSA's guidelines come as automakers race to put autonomous driving systems on the road and regulators scramble to keep up.

The companies that have the best safety approach will help NHTSA eventually write binding regulations, Rosekind said.

Rosekind said last month his agency wants Alphabet Inc's Google unit, Uber Technologies Inc [UBER.UL], Tesla Motors Inc and others to answer safety assessment questions within six months about self-driving vehicles and systems such as Tesla's Autopilot, which allows limited hands-free driving.

(Reporting by David Shepardson. Editing by Joseph White and David Gregorio)