SAN FRANCISCO — More than a decade after Google started experimenting with driverless cars, Waymo, the autonomous vehicle unit of Google’s parent company, Alphabet, says it has raised $2.25 billion, mostly from outside investors.

Waymo, which was spun out from Google in 2016, said on Monday that the funding had been led by the private equity firm Silver Lake, the Canada Pension Plan Investment Board and the Abu Dhabi state investment arm, Mubadala. The company did not disclose at what valuation the investors acquired a stake in it.

Waymo has been expanding efforts to commercialize its technology. In 2018, it started a self-driving taxi service in Arizona. On Monday, Waymo said it planned to start a delivery service, Waymo Via, which would use a fleet of autonomous vehicles and self-driving long-haul trucks.

After starting out as a research and development project at Google in 2009, the company has invested billions of dollars in developing the technology. Many in the industry consider Waymo to be the clear leader in autonomous vehicle technology.