Senate Democrats are pushing back against attempts to pass a compromise bill in the lame-duck session that could speed the introduction of driverless cars onto U.S. roadways, saying it lacks safeguards that would protect drivers.

“Many provisions still do not go far enough to protect American consumers,” Sen. Richard Blumenthal (D-Conn.), said of the American Vision for Safer Transportation through Advancement of Revolutionary Technologies Act, or AV START.

“We can do better,” said Sen. Edward J. Markey (D-Mass.).

The fight over the bill pits some automakers, which have argued that less regulation will speed the advent of autonomous vehicles, against safety advocates and states that say Washington should exert a firm hand in regulating the budding industry.

The automakers’ argument: The sooner fully autonomous vehicles reach the road, the sooner the 40,000 annual traffic deaths on U.S. roads will decline. But some states and consumer advocates demur, saying that if the federal government does not step in to regulate, states will need to — potentially leading to a patchwork of rules across the country.

Their concern also reflects, in a sense, the metamorphosis of autonomous vehicles from today’s models, with driver-assist systems that alert when a car may be in danger, to fully autonomous cars that may not need steering wheels or pedals on the floor.

There are several steps imagined between today’s models and those that no longer need a driver. Those distinctions may be glossed over by the public, which surveys show remains wary of driverless cars, after a trio of high-profile crashes this year involving the vehicles.

In March, Elaine Herzberg’s death as she pushed her bike across a dark four-lane roadway in Tempe, Ariz., was described as “the first recorded case of a pedestrian killed by a self-driving car.” Though a driver was behind the wheel of the Uber vehicle, a video inside the car showed he was inattentive during the crash, and software showed the system detected Herzberg but did not identify her as a person.

Two months later, also in Tempe, a Waymo test car with a human at the wheel was involved in a crash when another motorist swerved into it. Another Waymo vehicle that was not in autonomous mode and had an operator controlling it was in a five-car crash in nearby Mesa in June. Police said a drunk driver ran through a red light and plowed into the Waymo car and other vehicles.

After Herzberg’s death, Sen. John Thune (R-S.D.) said Congress needed to address autonomous vehicles to “update rules, direct manufacturers to address safety requirements, and enhance technical expertise of regulators.”

Despite the support of Thune, chairman of the Senate Commerce Committee and an author of the legislation, the bill languished in his committee as Democrats including Blumenthal, Markey and Sens Dianne Feinstein (D-Calif.)., Kirsten Gillibrand (D-N.Y.) and Tom Udall (D-N.M.) raised objections

“We can promote innovation and usher in the era of autonomous vehicles while enhancing safety, cybersecurity, and privacy,” Markey said, adding that he appreciated recent efforts to add consumer protections to the bill. “I cannot support this legislation without a meaningful sunset ensuring Congress can revisit this issue in the future and incentivizing [the National Highway Traffic Safety Administration] to establish and enforce safety, cybersecurity, and privacy protections.”

Sen. Gary Peters (D-Mich.), the Detroit-area co-sponsor of the Thune bill, has been making the rounds to lobby his Democratic colleagues.

Blumenthal said that the latest draft “represents progress” but that “my colleagues in both the Senate and House need time to more thoroughly review such a significant piece of legislation.”

“I greatly value the effort Senators Thune and Peters have made to address my serious concerns with earlier versions,” Blumenthal said, but he added that “many provisions still do not go far enough to protect American consumers.”

A group representing trial lawyers — now known as the American Association for Justice — initially supported a GOP revision that would preserve the right to bring a legal claim under state law, making it less likely that car-crash victims would be forced into arbitration.

“However, after we have had the opportunity to review the entire bill, we believe several of the new sections added will negatively impact consumer, passenger and roadway user rights if enacted,” the group said.

Opponents of the bill also object to provisions that prevent NHTSA from recalling cars based on safety reports submitted by automakers. And they say that a ban on the release of trade secrets by the Transportation Department will prevent disclosure of vital safety information.

“Every single aspect of an autonomous vehicle is going to be deemed to be proprietary,” said a Capitol Hill staff member familiar with the bill who asked not to be identified to speak candidly about the sensitive negotiations.

A memo being circulated on the GOP side offers several compromises intended to placate those who object to the bill.

The memo, obtained by The Washington Post, proposes creation of an advisory council for highly automated vehicles to review safety, labor and environmental impacts. It clarifies the roles of state and local governments to enforce laws on the operation of motor vehicles. It would allow the secretary of transportation to continue to set and update vehicle safety standards.

While the original bill would increase the number of exemptions automakers could get from traditional federal safety standards from 2,500 a year to 80,000 “highly automated vehicles,” the staff memo of proposed amendments specifies that exempt vehicles “must maintain the same overall safety level, occupant protection level, and crash avoidance level” as any other car.

The memo also seeks to quiet concerns raised by Herzberg’s death, stipulating that autonomous cars must “identify, detect and respond” to pedestrians and bicyclists. It adds a requirement that makers of driver-assisted cars, known as Level 2 vehicles, report their crashes and educate the public about what their cars can and cannot do.

The memo also says the National Institute of Standards and Technology should consider the cybersecurity and privacy concerns expressed by carmakers and the public.