The big picture: The $4.2 billion figure doesn't include all the funds automakers are investing into developing their own new tech. A Brookings Institution report last year estimated that from August 2014 to June 2017, a total of nearly $80 billion was invested in the area by the auto industry and venture capitalists.

The big funding tends to go to companies building a full car — or close to it. Developing a brand new car model usually costs companies at least $1 billion, and up to $6 billion.

• Zoox: The company, which is building a fully self-driving car from scratch, has raised $790 million in funding to date despite still being in the private testing phase of its development.
• Cruise: As a startup building an autonomous driving system that could be installed in a car, Cruise raised less than $20 million before General Motors acquired it for nearly $1 billion. Since then, it’s expanded to building cars that are natively built to drive themselves (in partnership with GM), and has attracted a $2.25 billion investment from SoftBank ($900 million upfront), and more recently a $2.75 billion investment from Honda ($750 million upfront).

What's next: "Venture investors have begun to target early-stage startups working on specific AV use cases, such as managing a logistics AV fleet or enabling last-mile deliveries, rather than the technology underpinning autonomous mobility," Synapse Partners founder Evangelos Simoudis writes for Axios Expert Voices. "As large-scale AV fleets are deployed, these early-stage startups will become likely targets of the next acquisition wave."

Go deeper: Q&A with Trucks Venture Capital partner Reilly Brennan about the self-driving startup market