According to Waymo, the autonomous car unit of Google parent company Alphabet, John Krafcik is stepping down as managing director after five and a half years at the top.

In a statement, Waymo said the chief executive’s duties will be shared between two current executives at the company – Tekedra Mawakana and Dmitri Dolgov. Ms. Mawakana was Waymo’s chief operating officer, and Mr. Dolgov was the company’s chief technology officer prior to the promotion.

In a blog post announcing the move, 59-year-old Krafcik gave no reason why he was stepping down at the moment other than saying he was following “new adventures”. Waymo said it was Mr Krafcik’s decision and that he plans to remain an advisor to the company.

Mr. Krafcik, a longtime auto industry executive who oversaw Hyundai Motor’s U.S. operations, joined Waymo in 2015 when it was still part of Google. During his tenure, Google spun Waymo into a separate subsidiary of Alphabet, and the company raised more than $ 3 billion from outside investors, signaling greater independence from its parent company.

Google and Waymo have been driving self-driving car technology for more than a decade. Waymo has launched its own autonomous taxi service called Waymo One in the greater Phoenix area. The company has partnered with a handful of automakers, including Volvo and Jaguar Land Rover, to build its self-driving technology into their vehicles.

Ms. Mawakana joined Waymo four years ago as the global director of policy and has been the company’s operations director for the past two years. She previously held political positions at eBay, Yahoo and AOL.

Mr. Dolgov is one of the original employees who started Google’s self-driving car project in 2009 and is widely recognized as one of the leading technical experts in autonomous vehicle technology.