Driverless cars should have a fairly easy time getting the green light to operate on U.S. roadways, as long as they look and act like the vehicles people have been driving for the past century. Take away the steering wheel and brake pedal—as Google hopes to do from its self-driving car—and that vehicle is no longer street legal and probably would not be for some time, according to a new report from the U.S. Department of Transportation (DoT).

As carmakers move at full throttle on efforts to rethink the automobile, the DoT is scrambling to figure out how it can adjust decades of driver safety regulations to accommodate vehicles driven entirely by computers. DoT’s Volpe, The National Transportation Systems Center reviewed current Federal Motor Vehicle Safety Standards and concluded that increasing levels of automation for parking, lane changing, collision avoidance and other maneuvers is acceptable, provided that the vehicle also has a driver’s seat, steering wheel, brake pedal and other features commonly found in today’s automobiles.

Implementing more radical changes, such as using smartphone-control, replacing the windshield with large video displays or realigning seats so there is no clear “driver,” would prevent approval under current safety standards, according to the new report. The DoT likewise tries to envision the impact of other futuristic features on safety that include using illuminated vehicles instead of headlights for nighttime driving or eschewing turn signals and taillights in favor of wireless communication with other connected cars (neither of which would pass muster under existing standards).

Google’s parent corporation, Alphabet, Inc., is pushing back against the government’s assessment by arguing that the company’s artificially intelligent self-driving system could be interpreted as a vehicle’s driver. “Developing a car that can shoulder the entire burden of driving is crucial to safety,” said Chris Urmson, director of Alphabet’s self-driving car project, during a Congressional hearing on Tuesday. “We saw in our own testing that the human drivers can’t always be trusted to dip in and out of the task of driving when the car is encouraging them to sit back and relax.”

Urmson urged lawmakers on the Senate Committee on Commerce, Science and Transportation to create a legislative on-ramp that will get fully autonomous vehicles on the road as quickly as possible. He also called for the federal government to create national policies regulating driverless automobile safety, rather than leaving these decisions to individual states. So far, 23 states have proposed a total of 55 different laws related to autonomous vehicles. California, in particular, is at odds with Google because the state wants to ban driverless cars that do not have a licensed driver behind the wheel.

The DoT’s National Highway Traffic Safety Administration (NHTSA) last week announced a pair of public meetings this spring to help the agency draft driverless vehicle safety guidelines. The Obama administration has said it wants these rules to be available to states, policy makers and companies by July so they have a better idea of how to invest in their next-generation vehicles and infrastructure. Such guidance is also needed to help ensure that the nearly $4 billion the White House wants to dole out over the next decade to speed the development of autonomous vehicles is well spent.

As the regulatory situation plays out in the coming months, carmakers continue to buy into the autonomous movement. General Motors last week agreed to acquire Cruise Automation, a San Francisco–based maker of software for self-driving cars. GM has also said it is developing an autonomous version of the Chevrolet Volt plug-in hybrid. Not to be outdone, rival Ford Motor Co. on Friday launched a new Ford Smart Mobility subsidiary responsible for, among other things, developing autonomous driving technology.

Efforts to shut out human drivers notwithstanding, stepwise automation of various features offers a more realistic short-term view of how the shift to driverless cars will play out, according to Ragunathan “Raj” Rajkumar, a professor of electrical and computer engineering in Carnegie Mellon University’s CyLab and veteran of the university’s efforts to develop autonomous vehicles, including the Boss SUV that won the DARPA 2007 Urban Challenge. “The transition to roadways filled with driverless drones will be gradual,” he says. “People will buy cars with more and more autonomous features in the coming years until, sometime in the 2020s, the majority of vehicles on the road will for the most part be fully autonomous.”