Uber shipped its self-driving cars from California to Arizona on Dec. 22. (Courtesy of Uber)

On Wednesday afternoon, California regulators forced Uber to take its self-driving cars off the state’s roads for failing to obtain required permits.

On Thursday morning, Uber packed up the cars and shipped them to Arizona, where it expects to begin road tests in the coming weeks.

Uber’s move to a neighboring state highlights the patchwork of regulations emerging as states determine how self-driving cars should be tested for safety. In particular, states looking to adopt the technology early are making their roadways more welcoming to self-driving cars and those who make them.

Twelve state governments have passed legislation or issued executive orders related to autonomous vehicles, according to the National Conference of State Legislatures, though not all pertain to testing on public roadways. More could be coming in the new year.

“Right now there are only a handful of states that have statutes like this. Four or five years ago, it looked like there would be a lot more,” said James Anderson, a senior behavioral scientist at RAND, a nonprofit research institution. Now that these tests are taking shape, “states are more trying to think about how does this actually work in practice.”

California was among the earliest to pass laws governing autonomous vehicles. In 2012, it required companies testing the vehicles on its roads to obtain special permits and disclose certain information about how the vehicles perform. Some of the state’s more recent policy proposals have been criticized as onerous and stifling to innovation.

The California Department of Motor Vehicles rebuked Uber last week when the company began testing self-driving cars on public roads in San Francisco without obtaining the required permits. On Wednesday, the DMV revoked the automobile registrations for Uber’s fleet to halt the program.

“California’s testing regulations for autonomous vehicles strikes a balance between protecting public safety and embracing innovation,” the agency said in a statement. “These regulations were adopted two years ago, and they are working for the 20 manufacturers now testing more than 130 autonomous vehicles on California’s streets and roads.”

For its part, Uber acknowledged from the start that the decision to launch without a permit may rankle regulators. The company maintains that its vehicles do not meet the state’s definition for autonomous vehicles because they need an engineer and safety driver, who can take control of the vehicle, to operate on roads.

Uber is no stranger to public policy conflicts. The company rapidly expanded its popular ride-hailing service by often circumventing regulators and launching without the required approvals. That strategy has gotten Uber banished from some cities, both in the U.S. and abroad. In other cities where regulators tried to penalize or shutter the service, however, Uber leveraged its large and vocal user base to oppose such measures.

This time is different. Whereas before it relied on a network of contractors to use their personal vehicles, Uber owns its fleet of self-driving cars and employs those who operate them. That gives regulators new recourse, such as California’s decision to revoke registrations, that they didn’t have before.

The federal government and the states have historically overseen different aspects of automotive regulation. While Washington typically sets standards for safety and emissions, for example, states control licensing and insurance requirements. The National Highway Traffic Safety Administration sought to better define how those roles apply to self-driving cars in September when it outlined its expectations for autonomous vehicle technology.

Most state governments will convene early in the new year, and the issue is likely to wind up in general assemblies across the country. Nearly two-dozen states have taken up autonomous driving bills in the recent past, though most ultimately failed. Ohio, New Jersey and Pennsylvania already have legislation pending, NCSL data show.

Michigan became the latest to enact progressive self-driving laws when its governor approved a series of bills last month, and Detroit-based General Motors has already announced plans to take advantage of the policy change by launching tests there this winter.

“The key thing for us in the Michigan package is that it allows for us to test and ultimately deploy self-driving vehicles on the road without a driver being in the vehicle,” said Harry Lightsey, GM’s executive director of public policy on emerging technologies. “That’s of course the full potential for the technology. Having a path to be able to do that is certainly key to us being able to progress the technology.”

Read more from The Washington Post’s Innovations section.