Uber Technologies is getting out of the self-driving truck business. The company said it will halt development of its self-driving tractor-trailer system to focus all of its autonomous-vehicle research and development efforts on cars.

It's a significant shift -- one that suggests the company is feeling growing pressure to deliver self-driving taxis before it falls too far behind fast-moving rivals.

Here's what we know.

A front view of a white Volvo tractor-trailer truck with "OTTO" logo and visible self-driving sensor hardware. The truck is driving on the highway, but nobody is in the driver's seat.

Uber said it will shut down its Otto self-driving truck effort to focus on self-driving taxis. Image source: Anheuser-Busch InBev N.V.

A $680 million self-driving truck effort, now shut down

Trucks weren't originally part of Uber's business plan. But the company made a big splash when it acquired self-driving truck start-up Otto in 2016 for a reported $680 million, adding Otto's talent to its Pittsburgh-based self-driving research team.

The publicity continued later in 2016 when Otto partnered with Anheuser-Busch InBev's Budweiser brand, in what was billed as the world's first commercial shipment by self-driving truck. A self-driving Otto semi successfully took a trailer loaded with Budweiser beer from an Anheuser-Busch facility in Fort Collins, Colorado, to Colorado Springs -- a distance of about 120 miles.

A tractor-trailer truck on a rural road in Colorado. The white tractor has a large blue "OTTO" logo, whle the trailer carries Budweiser's logos in red and white.

Otto and Budweiser partnered on the first-ever self-driving beer delivery in 2016. Image source: Anheuser-Busch InBev N.V.

At the time, it looked like self-driving trucks were only a few years away. Uber seemed well-positioned to emerge as a leader in what could be a very lucrative space. Earlier this year, Uber said that it was planning to begin integrating self-driving trucks into its Uber Freight offering, using the automated trucks on longer trips to reduce costs.

But Uber's priorities -- and its leadership -- have gone through some big changes since that much-talked-about beer delivery.

Uber has a bigger priority than trucks right now

Many things have changed at Uber since it purchased Otto, starting with its CEO: Founder Travis Kalanick departed last year after a series of scandals. His replacement, Dara Khosrowshahi, has revamped Uber's culture and refocused Uber on its core ride-hailing business.

An official photo of Khosrowshahi. He's seated, smiling, wearing a jacket with no tie.

CEO Dara Khosrowshahi has brought Uber back to basics, refocusing on delivering profitable ride-hailing. Image source: Uber Technologies.

Now, though, Uber and Khosrowshahi are coming under considerable pressure. It's widely believed that Uber won't be profitable until its human ride-hailing drivers are replaced by robots, in the form of self-driving vehicles. The investment case for Uber assumes that it will use its existing business to establish itself as a major player in the coming world of automated urban mobility.

The problem: Uber is now at risk of being beaten to market by subsidiaries of not just one, but two big, well-funded rivals. Alphabet's (NASDAQ:GOOG) (NASDAQ:GOOGL) Waymo and General Motors' (NYSE:GM) GM Cruise have both announced plans to begin launching self-driving taxis at scale between now and the end of next year.

I'm sure that Uber's investors haven't been shy about sharing their concerns about the competition with Khosrowshahi and other Uber executives. Those concerns almost certainly ratcheted up the pressure on Uber's Advanced Technologies Group, which is charged with developing the company's self-driving system.

This is probably part of Uber's response to that fatal accident

That perceived competitive pressure may have been a factor in a fatal accident in March, in which a prototype self-driving Uber vehicle hit and killed a pedestrian -- exactly the kind of accident that self-driving vehicles are supposed to be able to avoid. Did the pressure lead Uber to rush to put a system on public roads before it was ready to operate safely?

Khosrowshahi has clearly been rethinking Uber's self-driving effort since that fatal accident. It now appears that he has decided to continue the internal effort to develop a self-driving vehicle system for ride-hailing -- and he's adding the truck folks to the effort.

Will it be enough to get self-driving Ubers deployed before GM and Waymo expand to dominate the U.S. market? We'll find out.