Self-driving cars are more likely to be a threat than a benefit to public safety because of unresolved technical issues, engineers and safety advocates told the U.S. government Friday, countering a push by innovators for expedited government approval.

Even a trade association for automakers cautioned the National Highway Traffic Safety Administration at a public meeting that a slower approach may be needed than the agency's plan to provide guidance in six months for deploying the vehicles on roadways.

There are risks to deviating from the government's traditional process of issuing regulations and standards, Paul Scullion, safety manager at the Association of Global Automakers, said.

Issuing new regulations takes an average of eight years, NHTSA has said.

Mark Rosekind, NHTSA's administrator, said the agency can't wait because self-driving technologies are already in cars on the road. He pointed to automatic emergency braking that can stop or reduce speed to avoid or mitigate a collision. Another safety option on some vehicles automatically steers vehicles back into their lane if they start to drift into another lane without the driver turning on a turn signal.

Rosekind emphasized that he sees self-driving cars as potentially game-changing technology that can someday save the lives of many of the more than 30,000 people killed each year on the nation's roads.

President Obama has proposed a 10-year, $3.9 billion automated technologies program, including large-scale pilot deployments of self-driving cars around the country.

A General Motors Co. official recently told a Senate committee that the automaker expects to deploy self-driving cars within a few years through a partnership with the car-sharing service Lyft. Google, a pioneer in the development of self-driving cars, is pushing Congress to give NHTSA new powers so that the agency can give the tech giant special, expedited permission to bring to market cars with no steering wheel or pedals.

But many of the people who addressed the meeting pointed to a number of situations that self-driving cars are still unable to handle. The technology relies on clear lane markings, and the poor condition of more than half the nation's roads may be beyond the abilities of self-driving cars.

Also, weather can interfere with the vehicle sensors. Self-driving cars can't take directions from a policeman. And the lack of consistency in traffic control devices — horizontal versus lateral traffic lights, for example — adds further complications.

Until the technology has advanced beyond the point where ordinary conditions are problematic, "it is dangerous, impractical and a major threat to the public health, safety and welfare to deploy them," said Mark Golden, executive director of the National Society of Professional Engineers.

There have been thousands of "disengagements" reported in road tests of self-driving cars in which the vehicles automatically turned control over to a human being, said John Simpson, privacy project director of Consumer Watchdog.

James Niles, president of Orbit City Lab, a New York think tank, told the meeting that there is a complete absence of federal regulations to prevent self-driving cars from being turned into weapons by "bad actors."

"The concern that an autonomous vehicle could be used as a weapon has gone unnoticed by the general public and probably by the majority of government officials," he said.

-AP