After months of speculation that the company is developing automotive technology, Apple has officially leapt into the war for self-driving cars by obtaining a test permit from California regulators.

The permit allows Apple to begin testing up to three 2015 Lexus SUVs similar to the type that Google uses for its autonomous cars.

By obtaining clearance from California's Department of Motor Vehicles, Apple is signalling that it is serious about pushing forward with self-driving technology despite reports last northern autumn that it was scaling back its ambitions.

California's DMV disclosed the permit on its website on Friday, which lists several dozen other companies that are testing self-driving technology. The group includes BMW, Ford, Honda, Nissan, Uber and others.

Like those other companies, Apple's test vehicles will have human drivers behind the wheel when they go out on public roads, according to California regulations.

Speculation surrounding an Apple automotive project has been bubbling for years, with Apple keeping a tight lid on its plans.

The project quickly became something of an open secret among technology-watchers, even if it was never truly clear what Apple was working on. The ambiguity surrounding the effort was reflected in the numerous names that circulated about the project, such as the "Apple Car", "the iCar" and "Project Titan".

Some predicted that the company would itself be producing driveable vehicles. Others said Apple was more likely focusing on software that could be used to control a car, or to upgrade a car by injecting it with autonomous capabilities.

Some reports suggested Apple's new vehicle could be powered exclusively by battery-electric technology, much like cars produced by Tesla.

A 2015 hiring spree at Apple for automotive engineers prompted another wave of rumours. Some of the new hires came from companies such as Ford and Tesla, who are also researching self-driving technology. But by last October, many in the team had reportedly left or been reassigned as a result of a strategic shift by the company to focus on the software side of self-driving technology.

Despite the permit, it's still unclear what specific aspect Apple is working on.

Apple declined to comment, referring to public remarks that it had submitted to federal highway authorities in November on its research into automation.

"There are many potential applications for these technologies, including the future of transportation, so we want to work with NHTSA to help define the best practices for the industry," Apple wrote to the National Highway Traffic Safety Administration.

With its permit, Apple is leaping into an increasingly competitive race to build the world's first mainstream self-driving car.

On Thursday, General Motors announced that it plans to expand its self-driving autos unit with 1100 additional jobs and a $US14 million ($18.5 million) investment, and in February Ford said that it was investing $US1 billion in an artificial intelligence company called Argo AI.

Self-driving technology has the potential to reshape how people work, play and commute; proponents say automating vehicles will help reduce congestion and prevent crashes caused by human error, which according to federal statistics account for 95 per cent of all accidents.

Analysts said that Apple may accelerate the arrival of a fully autonomous car to the market.

"It's encouraging to hear Apple is still in the autonomous vehicle game," said Rebecca Lindland, executive analyst at Kelley Blue Book. She added that Apple's entry into the self-driving wars would push the industry to "provide a product that's not only safer, but more secure at a potentially even faster timeline than we're already experiencing".

Several automakers, technology hardware firms and software companies have applied to test cars through California's autonomous car program, according to the California Department of Motor Vehicles' website.

Companies that wish to test vehicles must provide evidence that they can train qualified employee drivers, can insure their cars and will be liable for any damage incurred during tests. They are also required to submit regular reports outlining any accidents that happen during testing and times that drivers turn off a vehicle's autonomous systems during a test.

This is not the first time Apple has leapt into the automotive space. Its CarPlay interface, for example, allows drivers to connect their vehicles with their iPhones - a foray into the market for in-car infotainment that is becoming increasingly common in consumer automobiles.

The Washington Post