No longer confined to the realm of science fiction, driverless vehicles are beginning to show up on American highways, with California, Nevada and Florida already legalizing their use.

With other states likely to follow suit, federal regulators have begun contemplating rules for automated automotive technology and are studying how the technology’s building blocks can be used to make the nation’s roads safer.

That sets the stage for Congress to look at legislating driverless technology as lawmakers begin writing a new surface transportation authorization next year.

For now, executive branch regulators are urging caution in rolling out the driverless cars.

“We’re encouraged by the new automated-vehicle technologies being developed and implemented today but want to ensure that motor vehicle safety is considered in the development of these advances,” David L. Strickland, head of the National Highway Traffic Safety Administration, said last month in announcing his agency’s first policy guidance on automated vehicles.

There’s been no driverless car legislation offered in Congress — so far.

But Mountain View, Calif.-based Google Inc.’s multimillion-dollar bet on a driverless car has brought attention to the technology in recent months. Google was responsible for guiding legislative efforts in Nevada, the first state to explicitly allow driverless vehicles.

The first license to test the Google vehicles was issued a little more than a year ago and carried such caveats as a requirement that such vehicles only be operated on public roadways with a driver and a passenger present. Last May, the famed “Google car” that can navigate its way around town — albeit with obvious modifications — made its way to Capitol Hill for a demonstration.

While driverless technology is still in the development stage, the work is progressing quickly. On this year’s auto show circuit, German luxury maker BMW said its i3 all-electric concept, set to go on sale next year, will include a system capable of piloting the car through stop-and-go traffic up to 25 miles per hour, though the driver must keep one hand on the wheel.

The NHTSA’s 14-page guidance issued last month suggested that — for now at least — fully automated vehicles on public roads be restricted to tests. But the agency also recognized that many of the building-block technologies for the fully automated vehicles of the future are already commonplace and represent steps forward for safety.

Among those technologies are such things as rearview backup cameras and lane-centering systems that are readily available on many luxury models. Other systems, such as electronic stability control, will soon be mandatory in new cars.

The fledgling efforts by regulators to set parameters for self-driving has led developers to ask Capitol Hill for help in shaping future policy.

Mitch Bainwol, head of the Alliance of Automobile Manufacturers, said at a Senate Commerce Committee hearing last month that it was important for Congress to make sure safety regulations addressing problems such as distracted driving don’t interfere with driverless-vehicle development.

Bainwol warned that poorly conceived policy “will chill innovation and bias drivers toward the use of handheld devices, rather than integrating devices with in-vehicle systems.”

Peter F. Sweatman, director of the University of Michigan’s Transportation Research Institute, also said investment in such technology will be critical to having state-of-the-art transportation infrastructure.

“Our transportation system will not remain internationally competitive without it,” Sweatman said.

If the latest efforts to shape the future of driverless-vehicle policy seem a bit “Back to the Future,” that’s because they are.

A 1991 surface transportation law (PL 102-240) authorized $650,000 to develop driverless technology. A group of nine stakeholders dubbed the National Automated Highway System Consortium used 10 mid-’90s Buick LeSabre sedans and some clunky last-century laptop computers.

Aimed at providing a solution to congested freeways, the development project managed to produce an operable automated ride by 1997. The resultant futuristic vehicle — a Buick that drove itself — garnered lots of media attention at the time.

But, as the Los Angeles Times reported, taking the driver out of the equation didn’t make the car any less vulnerable to failures of old-fashioned auto technology. One of the LeSabres used at a media event on Interstate 15 near San Diego was forced to the shoulder when its radiator burst.