That's roughly as many employees as Apple had in 2005, a company that was making laptops, desktops, servers, wireless routers, portable audio players, and entire operating systems.
I doubt a scrappy "startup" like Uber can beat companies like Toyota, Volkswagen, GM, Google or even Apple to market with a viable, certified self-driving car. They have, at best, a few billion left to dump into that venture. Those big companies could throw in ten times that if they wanted to.
Maybe someone needs to disrupt Uber. Go Lyft!
Other than engineering they also have a lot of people going around mapping cities, QAing those maps etc.
Ps... you'd crap your pants if you knew how many contractors they have doing operations work. Their mostly in low cost counties like the Philippines, and Brazil. Nothing about support scales with growth.
If their average employee costs them $500,000 a year (surely a generous estimate), then that's $125k per quarter. A $2B spend on salaries would suggest then that they had 16,000 employees (not counting drivers, who aren't part of this equation -- they're the difference between the $9.7B "gross bookings" and the $2B net revenue).
Uber employs apparently "more than 12,000 people," which is shocking, but salary still can't plausibly be the entire story here.