Uber's self-driving car unit lost $20 million a month. That's normal.

Newly unsealed court documents reveal that Uber's self-driving car unit was burning through $20 million a month in the run-up to this year's expected IPO.

The bottom line: Self-driving cars require billions of dollars of investment, with no guarantee of success. Many companies will lose their shirt.

"The figures, dating back to 2016, paint a picture of a company desperate to meet over-ambitious autonomy targets and one that is willing to spend freely, even recklessly, to get there," TechCrunch's Mark Harris reports.

My thought bubble: What's the big deal?

• GM Cruise lost $728 million in 2018.
• Ford lost $674 million on its mobility segment, including AVs.
• Lyft, which filed its IPO documents last week, spent $300 million on R&D in 2018 — up 120% over 2017 because of its ambitious AV push.
• Aurora Innovation just raised $530 million for AV development, and Nuro raised $940 million to develop driverless delivery vehicles.

Go deeper: Lyft beats Uber to IPO as ride-hailing rivalry heats up