Self-Driving Cars for Testing Are Supported by U.S. Justin Sullivan/Getty Images A self-driving car outside Google headquarters in California. SAN FRANCISCO - Companies from Silicon Valley to Detroit to Germany are developing cars that park, steer and even drive themselves. Now the federal agency for traffic safety has said it wants to come along for the ride. On Thursday, the Transportation Department made its first formal policy statement on autonomous vehicles. In a nonbinding recommendation to the states, it said that driverless cars should not yet be allowed, except for testing. But it said that semiautonomous features, like cars that keep themselves centered in lanes and adjust their speed based on the location of the car ahead, could save lives. The statement, from the department's highway safety agency, comes as companies, led by Google, have made significant technological strides in making cars that drive themselves, but still face daunting legal, regulatory and cultural hurdles before the cars are widely available to drivers. It is the latest example of the tension between technological innovation and regulation, which move at very different speeds. It is also a time of rapid change, and some anxiety, about autonomous systems in general. The transportation department is struggling, for instance, to determine how to regulate drone aircraft. The statement detailed the benefits of self-driving and semiautonomous cars, which analysts said was a recognition by government officials that it had no choice but to keep up with the advancing technology in this area, which falls on a continuum from cruise control to full automation. "It's not that they're trying to put the brakes on it," said Richard Wallace, director of transportation systems analysis at the Center for Automotive Research in Ann Arbor, Mich. They're trying to get out in front of it. Still, the highway safety agency was careful to address the tension between technology and regulation. "Any potential regulatory action must appropriately balance the need to ensure motor vehicle safety with the flexibility to innovate," it said. Even though technology companies like Google generally fear that innovation far outpaces regulation and risks being stifled by it, it has a different approach with cars than with software or cellphones because cars have been heavily regulated for decades, said Ryan Calo, a law professor at the University of Washington who co-founded the Legal Aspects of Autonomous Driving center at Stanford. "We want to have some experimentation in the states to see what works, but it's nice to have federal experts helping out, as long as they don't take it too far," he said. Autonomous cars could increase safety because they are not subject to human error like disobeying traffic laws and falling asleep at the wheel, according to analysts, car companies and the transportation department. They could also offer mobility to people who cannot drive, like the disabled or the aging. Driverless cars could "change our lives, give us more green space, mobility, fewer hours wasted," Larry Page, Google's chief executive, said this month. The average American spends 50 minutes commuting. Imagine if you got that back. Still, many Americans are dubious about automated driving, according to a poll by the Auto Alliance, a Washington trade group that represents 12 of the largest carmakers selling vehicles in the United States. For instance, 81 percent said they were concerned that computer hackers could take control of an automated vehicle. Even if automated cars were safer, people would worry about the lack of human judgment, Mr. Calo said. "The first time that a driverless vehicle swerves to avoid a shopping cart and hits a stroller, someone's going to write, "robot car kills baby to save groceries," " he said. It's those kinds of reasons you want to make sure this stuff is fully tested. Yet most people will have the option of buying a car that is part robot in some sense next time they visit a dealership. Vehicles ranging from German luxury cars to mass-market American sedans are now equipped with automated safety systems, which rely on computer processors, software and sensors. Future models from Mercedes-Benz have radar systems that brake a car in the event of an impending collision, stay in its proper lane around curves and sense when a driver is fatigued. Ford Motor Company's midsize Fusion sedan has a lane-assist system that alerts drivers when they stray on the roadway. Many cars come with adaptive cruise control that automatically cuts the speed when the distance between vehicles gets too close. Claire Cain Miller reported from San Francisco and Matthew L. Wald from Washington. John M. Broder contributed reporting from Washington and Bill Vlasic from Detroit. A picture caption last Friday with an article about the federal Transportation Department's stance on driverless vehicles rendered incorrectly part of the name of a vehicle shown at the Consumer Electronics Show in January. It was a Lexus LS 600 Integrated Safety driverless research vehicle, not a Lexus SL 600.