An expert on autonomy has told American legislators that automakers should slow down when it comes to autonomous-car technology.

Mary Cummings, the director of the Humans and Autonomy Laboratory at Duke University, told a panel of legislators on Tuesday that automakers and suppliers are bringing autonomous driving technology to market without enough testing.

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Cummings praised Google for having done testing for more than 1 million miles, but she said a Rand Corp. study shows that at least 275 million miles of testing, with no fatalities, is needed before the tech will be fully ready for the market.

“That means we need a significantly accelerated self-driving testing program, but it is not simply good enough to let these cars operate in California or southern Texas to accrue miles,” Cummings said before the panel made of members of the Senate Committee on Commerce, Science, and Transportation.

Even those who are working to develop the tech acknowledge there are obstacles, such as the state-by-state variances in the laws that govern autonomous driving and testing.

“If every state is left to go its own way without a unified approach, operating self-driving cars across state boundaries would be an unworkable situation and one that will significantly hinder… the eventual deployment of autonomous vehicles,” said Chris Urmson, head of Alphabet Inc’s Google self-driving car program, before the committee.

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General Motors, Lyft, and Delphi are all companies that are supportive of a national policy regarding autonomous cars.

The National Highway Traffic Safety Administration (NHTSA) started to do away with some regulatory challenges at the beginning of this year and is planning to have guidelines for autonomous vehicles out by June, while also working on a model autonomous-driving policy that can be used as an example by states.

Meanwhile, Massachusetts Senator Edward Markey (D) is asking for policies and rules that will protect the privacy of consumers, while also protecting autonomous vehicles that use the Internet from hacking and other security intrusions.

According to Cummings, NHTSA has a challenge that the private sector doesn’t – resources.

“The government cannot hire the same people that Chris [Urmson] is hiring at Google X,” Cummings told the panel.