A House panel on Wednesday unanimously advanced a sweeping proposal that would carve out new exemptions for thousands of experimental autonomous vehicles from existing federal auto safety standards, marking Congress's most significant attempt at legislating driverless cars.

The measure, which would preempt a budding patchwork of state regulations setting performance standards for the cars' mechanical, software and safety systems, is designed to expedite autonomous vehicles' entrance to market.

The US House Energy and Commerce Subcommittee on Digital Commerce and Consumer Protection greenlighted the legislation by unanimous voice vote after Republicans adopted Democratic provisions to stiffen safety oversight of autonomous vehicles by federal officials.

Democrats pushed for a raft of tighter safety measures, including a requirement that the National Highway Traffic Safety Administration develop a formal regulatory framework within 18 months. The agency would have to formalize and make publicly transparent the process for granting exceptions to autonomous vehicles from Federal Motor Vehicle Safety Standards (FMVSS).

As written now, the bill would allow automakers to deploy as many as 100,000 autonomous vehicles that do not strictly meet current safety thresholds which have prevented the sale of cars lacking conventional human controls. The cars would not require pre-market approval from federal regulators, but would require automakers to submit safety assessment reports.

While Democrats on the panel supported the proposal, they signaled an intention to further tweak the bill when it comes up for markup by the full Energy and Commerce Committee, possibly as early as next week.

By pointedly barring states from adopting individual safety and cybersecurity frameworks, the bill marks a major victory for automakers and technologists, who argued that the emerging web of state rules would decelerate the technology's testing and deployment.