The California Department of Motor Vehicles has today revoked the registrations for Uber's fleet of 16 self-driving cars, forcing the company to remove the vehicles from the streets of San Francisco where they were being used. The move comes after Uber refused to apply for a $150 permit that would designate the cars as test vehicles, and allow them to be used on Californian roads, with the company arguing that the documentation didn't apply to its specific self-driving cars.

In a statement, an Uber spokesperson confirmed the company had stopped its self-driving pilot in California after the registrations were revoked. "We’re now looking at where we can redeploy these cars," the spokesperson said, "but remain 100 percent committed to California and will be redoubling our efforts to develop workable statewide rules.”

The revocation of the registrations means that Uber cannot legally use its vehicles on San Francisco roads, but the California DMV indicates that it will be able to restart its self-driving ride-sharing service in the city once it has secured the relevant permit. In a letter to Uber's Davis White, Jean Shiomoto — the director of the California DMV — said that the agency "stands ready to work with [Uber] collaboratively," and that the "autonomous vehicle testing application process is simple and straightforward."

Shiomoto's letter also includes a link to the permit application, and promises that a team will be on hand to assist Uber in obtaining the permit, which the DMV says can take less than 72 hours to issue. "The DMV fully supports the advancement of autonomous technologies," Shiomoto says in the letter, specifying that it "holds the promise of enhanced safety and mobility," but that it also "must be tested responsibly."

The letter also notes that Uber is apparently interested in applying for the permit in question. Uber had previously pointed to the differences in its self-driving vehicles — which usually navigate around San Francisco streets automatically but have human "safety drivers" on board — as a reason to avoid applying for the documentation. “You don’t need to wear a belt and suspenders and whatever else, things that don’t apply, if you’re wearing a dress,” Uber VP of engineering Anthony Levandowski said earlier this month. “If you’re driving a car, you don’t need a fish and game permit.”

Uber may say that its self-driving cars don't need test permits, but their functionality still seems to be a work in progress. Several traffic incidents were spotted by other road users within days of the cars' arrival on Californian streets, with camera footage showing them blowing through red lights, and programming faults identified that could see them making potentially unsafe turns in bike lanes.