General Motors-backed Cruise reports it is delaying the rollout of its driverless taxi service. The company said previously the service would start by the end of 2019.

In a recent blog titled, “The Next Steps to Scale Start in San Francisco,” Dan Ammann, Cruise CEO, explains the trials and tribulations of testing and validating the next generation of autonomous vehicles.

In the post, Ammann alludes to the fact that the safety tech isn’t yet in place for deployment:

“When you’re working on the large-scale deployment of mission critical safety systems, the mindset of ‘move fast and break things’ certainly doesn’t cut it” he writes. “With such high stakes, our first deployment needs to be done right and we will only deploy when we can demonstrate that we will have a net positive impact on safety on our roads.”

The post states that Cruise will be increasing testing and validation of its fleet of all-electric self-driving cars, though it does not update a new launch date for the service.

In the post, Ammann cites Cruise’s milestones to date, including scaling from 40 people to 1,500 since 2016 and raising $7.25 billion in the past year. “Today, we are the only company with self-driving cars that are manufactured on a large scale automotive assembly line to the same rigorous standards of safety and quality as any other production car,” Ammann writes.