DETROIT — In a policy statement released Thursday, America’s top auto-safety agency embraced self-driving technology but called for states to make sure there is still a person behind the wheel while such innovations are in testing.

The National Highway Traffic Safety Administration issued a 14-page preliminary policy statement on automated vehicles to address the issues arising from technology already developed that makes it possible for the car to do the accelerating, steering and braking.

Much of the technology already exists in modern cars. With such “driver assistance” features, sensors in a car can detect other cars, lanes and pedestrians. If the driver fails to react, the technology can take control of the car and make the necessary evasive action to avoid a collision.

Transportation Secretary Ray LaHood has been a proponent of the new safety technology, which he considers less prone to mistakes than a driver. But as states permit the testing of autonomous vehicles, the safety agency wants to err on the side of caution. Until there is more data, NHTSA recommends self-driving cars continue to be used for testing only and that the driver be in place to manually override controls if necessary.

“Whether we’re talking about automated features in cars today or fully automated vehicles of the future, our top priority is to ensure these vehicles — and their occupants — are safe,” LaHood said.

NHTSA encouraged further research, describing automated driving systems as a chance to improve safety on the road.