The U.S. Senate Commerce Committee on Wednesday unanimously approved a bill to speed self-driving cars to market without human controls and bar states from imposing regulatory road blocks.

The bill still must be approved by the full Senate. The U.S. House passed a similar version last month unanimously. General Motors Co, Alphabet Inc, Ford Motor Co and others have lobbied for the landmark legislation. Despite some complaints from Republicans, the Senate bill does not speed approval of self-driving technology for large commercial trucks after labor unions raised safety and employment concerns.

The measure, the first significant federal legislation aimed at speeding self-driving cars to market, would allow automakers to win exemptions from current safety rules that prohibit vehicles without human controls.

States could still set rules on registration, licensing, liability, insurance and safety inspections, but not performance standards.

Senator Richard Blumenthal sought to amend the bill to require companies to include human controls in the event of an emergency, but in the face of opposition dropped the proposal. Some senators argued it would be more dangerous to allow human drivers to seek to take over driverless cars.

Several Republican senators noted the strong support of trucking organizations to include vehicles over 10,000 pounds, but Democrats made it clear that they would not support the bill if it included bigger vehicles.

Auto safety advocates complained that the bill lacked sufficient safeguards. It would within three years allow automakers to sell up to 80,000 self-driving vehicles annually if they could demonstrate they are as safe as current vehicles.

The bill’s phase-in schedule was revised to allow 15,000 per manufacturer and up to 80,000 after three years, down from 100,000 proposed earlier. It would lift the cap completely after four years.

The bill grants NHTSA authority to exempt vehicles from existing federal safety requirements and the agency would have to make a determination within six months of getting a request.

The Commerce Committee adopted a House approved provision that would require automakers to eventually include a rear seat alert system designed to warn parents not to forget young children in car seats.