Cruise Automation has suffered another setback as the company has delayed plans to launch its autonomous ride-hailing service.

In a lengthy Medium post, Cruise CEO Dan Ammann said the company still has work to do before the company can launch its Waymo One competitor.

As he explained, “In order to reach the level of performance and safety validation required to deploy a fully driverless service in San Francisco, we will be significantly increasing our testing and validation miles over the balance of this year.” This additional testing means the “timing of fully driverless deployment” will be pushed pasted their previous deadline of 2019.

Ammann didn’t go into specifics, but said the additional testing will benefit the company as “running many more miles on the road will further accelerate our rate of learning and safety validation.” He also said the company will be testing a larger fleet of autonomous vehicles and this will help them gain “crucial operational learnings” from both the size of the expanded fleet and its employee-only ride-hailing service.

While the executive didn’t go into too many details, he described San Francisco as “one of the most complex urban environments” for autonomous vehicles. As he explained, the city is more than 40 times more challenging than a suburban setting. This obviously presents a challenge for the company, but Ammann said once cars are safely deployed at scale in San Francisco, the company can “quickly expand everywhere else.”

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Ammann also said the company is being careful as Silicon Valley’s mindset of “move fast and break things” doesn’t cut it when you’re talking about autonomous vehicles. Instead, the first deployment has to be “done right” and will only occur when the company is confident there will be a “net positive impact on safety.”