Apple has joined the list of companies with permits to test self-driving cars in California. The iPhone maker has disclosed little about its ambitions when it comes to self-driving vehicles, with its Chief Tim Cook hinting at plans, but the company declining to comment for news reports on long-idling rumors.

Late last year, Apple revealed it was investing heavily in autonomous vehicles, in a letter asking the government to make it easier to develop self-driving cars. Apple issued the letter because it is "investing heavily in machine learning and autonomous systems," an Apple spokesman said in an email to AFP at the time.The California-based tech giant is expected to focus on software systems, letting partners manufacture vehicles, but would understandably want to be able to test its navigation technology in cars.

Most major auto manufacturers and many technology groups are currently developing autonomous vehicles, considered to be the future of the automobile, along with electric power, with first production models promised for around 2020. Meanwhile, Chinese tech giant Baidu, which is also working on autonomous driving at its California research center, announced this week, the acquisition of xPerception, a U.S. startup that develops visual perception software, along with services and devices for people who are visually impaired.