Google ultimately concluded that partially self-driving cars were a technological dead end. Instead, the company set itself a goal to build a fully self-driving vehicle — one that was so reliable it would never need intervention from a human driver.
Urmson, the former Google engineer, believes that driver assistance and full self-driving are "actually two distinct technologies."
"In a driver-assistance system, most of the time it's better to do nothing than to do something," Urmson said in an April talk. "Only when you're really, really, really sure that you're going to prevent a bad event, that's when you should trigger. That will guide you down a selection of technologies that will limit your ability to bridge over to the other side."
In contrast, Waymo is trying to build cars that never hand off control to a human passenger. That means the software has to be able to choose a reasonable, safe response to every conceivable situation. And it means building in redundancies so that the car can respond gracefully even if key components fail.
"Each of our self-driving vehicles is equipped with a secondary computer to act as a backup in the rare event that the primary computer goes offline," Google wrote in a 2016 report. "Its sole responsibility is to monitor the main computer and, if needed, safely pull over or come to a complete stop. It can even account for things like not stopping in the middle of an intersection where it could cause a hazard to other drivers."
Building software that can gracefully handle any contingency — and redundant, bulletproof hardware — is a much harder technical problem than building driver-assistance technology that counts on humans to handle tricky situations. But it also has a big upside: If the car never transfers control to a human driver, then it never has to worry about the driver being caught unprepared.
For now, Waymo does still have drivers behind the wheel, but these drivers are Waymo employees with special training on handling self-driving vehicles, who are presumably paid to continue paying attention to the road no matter how boring it gets. And in recent months, the job has been getting pretty boring. According to a regulatory filing, Waymo's self-driving cars drove more than 600,000 miles in California and only had to hand over control to a human driver 124 times.
That works out to one disengagement every 5,000 miles, a four-fold improvement over 2015, and by far the best showing of any company testing on California roads. At that rate of progress, it'll take a few more years for Waymo to surpass human levels of driving safety. If the California data is any indication, rivals like GM, Ford, BMW, and Mercedes have a lot of catching up to do.
While Waymo seems to be the clear leader in self-driving technology right now, the company is taking a big risk by trying to jump straight to full self-driving technology. Reaching the necessarily level of reliability — going from 99.99 percent reliability to 99.9999 percent, say — might take several more years. During that time, companies taking a gradualist approach could steadily gain ground.
One big advantage of the gradualist approach is that it can allow car companies to collect a lot of data, and many experts believe that having a lot of data is crucial for building successful self-driving cars. Waymo's cars have driven more than 3 million miles on public road, providing the company with the raw data they use to tune their software algorithms. in contrast, Tesla has collected more than 1 billion miles of real-world sensor data from its customers' cars. All that extra data could allow Tesla to make more rapid progress toward a goal of full autonomy, allowing it to eventually catch and surpass Waymo's early lead.
works at Google.