Uber’s self-driving cars still aren’t very reliable, apparently.

Business Insider reports that Uber’s self-driving tech is still far behind competitors like Waymo. The report, which cites interviews with employees in Uber’s Advanced Technologies Group (ATG), compares the self-driving cars project to a “science experiment,” and says that the cars “perform reliably only on limited well-mapped routes, and aren’t making much progress on handling more.”

That may sound like a harsh assessment, but as BI points out, Uber has had other priorities besides autonomous driving alone. Since the company resumed testing its self-driving cars in December following a fatal accident in Arizona, Uber has been progressing much more slowly. It’s possible the cautious approach is frustrating to some employees, who may want to see more rapid improvements in the underlying technology rather than safety-related updates alone.

Something else that might be causing some strain internally: lack of involvement from Uber CEO Dara Khosrowshahi whose approach to ATG is reportedly seen by some as too hands-off.

At the same time, Business Insider notes that engineers in Uber’s ATG division are highly paid, with senior engineers pulling in as much as $400,000 a year. With pay like that, there’s little incentive to complain too loudly, as many employees hope Uber’s imminent IPO could make them even more money once the company’s stock begins trading publicly.

Still, if Uber’s self-driving cars really are that far behind, it should be a cause for concern. Uber is still very far from being a profitable company, something that self-driving cars could help change. (Unlike pesky human drivers, self-driving cars don’t need to be paid or be classified as employees.) But even Uber isn’t totally sure whether its self-driving cars will ever be viable. As the company noted in its IPO filing, the tech is “inherently risky” and may never come to fruition.