(TNS) -- For Uber's self-driving cars, it's 1 million miles down and likely millions more to go, autonomous vehicle experts told the Tribune-Review.

Uber announced Thursday that its fleet of more than 200 self-driving cars drove more than 1 million autonomous miles during its first year of steady testing.

Uber launched a pilot program last September in Pittsburgh to give rides in its fleet of self-driving Ford Fusions and later Volvo XC90s. The pilot program grew to Tempe, Ariz., and San Francisco.

“Uber's 1 million autonomous miles is a significant milestone, and happy much of it happened in Pittsburgh,” Stan Caldwell, executive director of Carnegie Mellon University's Traffic21 Institute, wrote to the Tribune-Review on Thursday. “I expect this real-world testing has greatly advanced Uber's technology, but to be confident in these systems, billions of miles will likely have to be tested.”

Uber is still way behind Waymo, the self-driving arm of Alphabet, Google's parent company. Waymo reported reaching 3 million miles in May. The company said it took six years — 2009 to 2015 — for it to reach 1 million miles.

Missy Cummings, director of the Humans and Autonomy Lab at Duke University, literally yawned when asked about the million-mile milestone. She pointed to testimony she gave in March 2016 in front of a Senate committee in which she noted the Rand Corp. suggests self-driving cars go 275 million fatality-free miles before they are verified as being just as safe as human drivers. She cautioned senators about putting too much stock in early successes.

“While I enthusiastically support the research, development and testing of self-driving cars, as human limitations and the propensity for distraction are real threats on the road, I am decidedly less optimistic about what I perceive to be a rush to field systems that are absolutely not ready for widespread deployment, and certainly not ready for humans to be completely taken out of the driver's seat,” Cummings told the committee.

Uber hasn't used its million-mile milestone to talk about the safety or reliability of its technology. And it shouldn't, said Mike Wagner, co-founder of Edge Case Research, a Pittsburgh company that tests and simulates autonomous software to identify and fix bugs and other weaknesses. Engineers at Uber are likely changing code daily, Wagner said.

“They are using these million miles to understand what type of system they should build,” Wagner said.

The company reported only minor fender benders and scrapes in Pittsburgh. Bad driving was caught on tape during the cars' debut in San Francisco and one was involved — but not at fault — in a crash in Tempe. Wagner suspected Uber engineers are looking at more than just the crashes or bad driving caught on tape. Any time a piece of hardware or software failed should be examined, even if the failure lasted just for a few seconds and nothing happened, Wagner said.

“Even over a million miles, effects like that might not result in full-blown collisions,” Wagner said.

Wagner said Uber's cars likely have seen a lot in their first million miles but questioned whether they have seen everything. He suggested the industry move away from mile counting and start talking about what systems the cars have and how they react to different scenarios.

There may be, however, just as many scenarios to test as there are miles to drive.

©2017 The Pittsburgh Tribune-Review (Greensburg, Pa.) Distributed by Tribune Content Agency, LLC.