Driverless cars came a step closer to reality Wednesday as the Senate Commerce Committee approved comprehensive legislation to clear the way for their introduction.

The bill — and similar legislation already approved in the House — seeks to clarify the role played by the federal and state governments in the autonomous car future. It spells out that states would continue to license, regulate insurance, and enforce traffic laws, but the National Highway Traffic Safety Administration would oversee the design and manufacture of the vehicles.

Like the House bill, the Senate legislation would allow Transportation Secretary Elaine Chao to exempt automakers from existing safety standards, eventually permitting the sale of 100,000 cars a year as the self-driving technology develops.

It also requires manufacturers to develop plans to protect autonomous cars from cyber attack. Both the House and Senate bills pertain only to development of driverless cars, and not to the prospect that driverless trucks may become a presence on the highways in 10 or 20 years.

Regulation of the rapidly emerging autonomous car industry has been controversial for several years. Automakers and independent developers of the vehicles generally have sought to be unencumbered by rules that might impede their progress, but they also have looked to states for permission to test their cars on the roadways.

Though the Senate bill gives Chao and NHTSA several oversight responsibilities, safety advocates have been fearful that the absence of regulations would allow unfettered development of the vehicles.

Aware of both arguments, NHTSA last year came out with a list of recommendations — NHTSA called it “guidance” — for the industry. The agency reserved the right to propose regulations as development continued, and Congress has taken on that role with bills in the House and Senate this year.

The Senate bill already has proved controversial.

Democratic senators and safety groups preempted Wednesday’s hearing with a media conference call Tuesday. Their concerns include the belief that provisions in the bill intended to prevent a patchwork of state laws will strip states of the ability to promote safety regulations. They want greater authority put in the hands of federal regulators.

“There are warning signs that this bill puts too much trust in the hands of automakers and places too little importance on consumer safety protections,” said Jackie Gillan, president of the group Advocates for Highway and Auto Safety, which organized the conference call.

Former NHTSA administrator Joan Claybrook said the bill “puts auto and tech companies in the driver’s seat.”

“It puts the federal auto safety agency in the back seat in terms of ensuring industry accountability,” Claybrook said.

The committee also heard from Deborah A.P. Hersman, who testified before them three weeks ago. Hersman, a former National Transportation Safety Board chairman who now heads the National Safety Council, urged the committee to include the trucking industry in the bill.

But the committee also heard at that hearing from the trucking industry, which maintains a powerful presence on Capitol Hill and has contributed $764,222 to incumbents this year. The truckers argued that their development of autonomous vehicles should be exempted from the legislation.

Hersman, who holds a commercial truck driver’s license, wrote to the committee after that decision, voicing her disappointment.

“Commercial trucks comprise four percent of all vehicles on the road but are involved in 11 percent of fatal accidents,” she wrote.

Hersman did commend the committee for including a provision that would help educate the public as autonomous cars begin to show up on roadways. A survey by AAA this year found that three-quarters of drivers said they would be afraid to ride in an autonomous car, and more than half of them wouldn’t feel safe sharing the road with a driverless car.