An autonomous vehicle has completed a 3,400-mile U.S. road trip with almost no intervention from drivers.

Auto supplier Delphi Corp. says the Audi Q5 fitted with radar, cameras and laser sensors drove itself 99 percent of the time from San Francisco to New York.

Drivers intervened once when traffic was weaving around in a construction zone, and again when the car didn't want to move into a busy left lane. But for the most part, it easily navigated bridges, traffic circles and open highways.

Delphi's chief technology officer Jeff Owens says that among other things, engineers learned that vehicle cameras need to be able to read a larger variety of lane markings.

Owens says the data collected on the trip will be used to improve future autonomous driving systems.