The US agency in charge of highway safety thinks that the autonomous car built by Google-parent Alphabet could qualify as being its own driver.

In a written response to a query from the Silicon Valley-based technology firm, the National Highway Traffic Safety Administration said that since the self-driving cars lacks steering wheels or other controls for humans, it is "more reasonable to identify the driver as whatever (as opposed to whoever) is doing the driving."

While the administration's response didn't change rules of the road, it is seen as a green light of sorts for getting autonomous vehicles to market.

"Our interpretation that the self-driving computer system of a car could, in fact, be a driver is significant," US Transportation Secretary Anthony Foxx said in a written statement release on Wednesday.

"But, the burden remains on self-driving car manufacturers to prove that their vehicles meet rigorous federal safety standards."

Foxx added that the NHTSA is "taking great care to embrace innovations that can boost safety and improve efficiency on our roadways."

Alphabet said that it is considering the letter and had no further comment.

The feedback, however, promises to be encouraging given the time and resources that Alphabet has poured into developing self-driving cars.

- California speed bump -

A potential bump in the road popped up in December, when California motor vehicle department officials proposed self-driving car regulations that included mandating that a person could take the wheel if needed.

A draft set of rules released by the California Department of Motor Vehicles for a public comment phase do not allow for legal operation of an autonomous car being tested by Google because it lacks a steering wheel or foot pedal controls.

"We're gravely disappointed that California is already writing a ceiling on the potential for fully self-driving cars to help all of us who live here," Google told AFP at the time.

California rules-of-the-road for self-driving cars have the potential to set precedent, and the proposed regulations are seen as sure to slow down the speed with which the technology goes mainstream.

The proposed California regulations call for a licensed driver to be in a self-driving car and able to take control in the event of a technology failure or other emergency.

Google has been testing self-driving cars on California roads for a while, and an array of automobile makers including Audi, Ford, Mercedes, Lexus, Tesla and BMW are working on building self-driving capabilities into vehicles.

The US administration pledged in January to help clear the way for autonomous vehicles with an investment of $4 billion to fund research and testing projects.