He's the latest in a growing list of executives to question the practice of driving millions of miles as a necessary part of testing. Executives from Aurora Innovation and Volvo Cars raised similar concerns last month during the Automated Vehicles Symposium, an annual gathering of industry leaders, government officials and academic researchers.

Miller's caution comes from personal experience. While working as an operations manager at Uber in 2018, he was alarmed that the company's self-driving test cars were "routinely in accidents resulting in damage" and that collisions occurred "every 15,000 miles." Those are passages from a prescient email to several Uber executives in which he outlined his concerns and urged a review of the self-driving program, particularly warning that human safety drivers needed to be better trained.

He sent that email on March 13, 2018. Three days later, Miller left his job.

Five days after he sent the email, an Uber self-driving test vehicle struck and killed Elaine Herzberg, a pedestrian in Tempe, Ariz., a death that continues to reverberate through the fledgling industry.

This year, Miller examined data from the Naturalistic Driving Study for the second Strategic Highway Research Program, a federal research initiative, and California crash reports. His analysis suggests automated vehicles are involved in more crashes than vehicles with human drivers. Companies should be tapping the brakes on their self-driving programs, he says, but too often, the culture doesn't empower such decisions.

"Basic ethics tells you that if you're putting people at risk like this, you need to stop," said Miller, who worked at Google's self-driving program and then at Otto, a self-driving trucking company that was acquired by Uber.

"It's hard for companies with these fleets with hundreds of vehicles to say, 'Hey, there's something wrong. We need to bring every single vehicle back and possibly stop for weeks and have hundreds of safety drivers sitting around.' But you need to be able to make that sort of decision."

Miller hadn't previously spoken publicly about his experience at Uber or his role as a whistleblower. He made the comments as part of a guest appearance on an episode of the "Shift" podcast to be published Monday, Aug. 19.

He suggests the industry needs to heed the warnings he delivered to Uber more than a year ago.

"What I think is lacking at multiple places in this industry is basically leadership that is willing to listen and make people comfortable bringing up these issues," he said. "More importantly, they also need to seek out these answers and approach drivers and the engineers and find out what the problems are."