Waymo, the self-driving arm of Google's parent company Alphabet, announced Monday that it has raised $2.25 billion in its first external round of funding. The investment was led by private equity firm Silver Lake Partners, the Canada Pension Plan Investment Board and the Mubadala Investment Company, the sovereign wealth fund of the United Arab Emirates. But company CEO John Krafcik said the investment will enable the company to add key partners and grow its operations. Advocates of self-driving vehicles say the technology will dramatically improve road safety. Its self-driving vehicles have driven more than 20 million miles on public roads.