Doug Field, the head of Apple's electric vehicle project (Project Titan), abruptly left the company to become the chief executive officer of Ford's advanced technology group. Field's departure casts doubt on the progress of Apple's efforts to develop self-driving car technology and builds given he is the fourth executive to leave the project in its seven year history. Apple has struggled to make progress in its goal of developing an autonomous vehicle, with delays, layoffs of engineers, and lack of a clear vision for the project. Field's exit leaves uncertainty around who will replace him and Apple's ability to successfully bring an electric vehicle to market.