The newspaper said the company has recently begun accelerating its efforts in the space and is planning to triple the 600-person team already working on the technology after investigating the area for a year.
Details of work at the secretive company are still thin on the ground, including exactly what type of car Apple is developing under the codename "Titan."
Apple has been talking with officials at the Contra Costa Transportation Authority over getting access to the Concord Naval Station. The former U.S. military base near San Francisco is being turned into an autonomous car testing facility called "GoMentum Station."
The company's first electric car won't be fully autonomous but that remains a long-term goal, said The Wall Street Journal.