More companies are trying to bring self-driving cars to the masses than ever before. Yet a truly autonomous vehicle still doesn't exist. And it's not clear if, or when, our driverless future will arrive. Proponents in the industry, including Tesla CEO Elon Musk, Waymo CEO John Krafcik and Cruise CEO Dan Ammann, touted an aggressive timeline but missed and reset their goals. In a third-quarter earnings call, Musk said Tesla "appears to be on track for at least an early access release of a fully functional Full Self-Driving by the end of this year." Other leaders in the field are taking a more sober view on driverless cars, what's still needed to perfect them and how long before they are part of our daily lives. Avideh Zakhor, a professor at the University of California at Berkeley's electrical engineering and computer sciences department, explained what inspired the rational reckoning in the industry: "There was a sense maybe a year or two ago, that 'Oh, our algorithms are so good! We're ready to launch. We're gonna launch driverless cars any minute.' And then obviously there's been the setbacks of people getting killed or accidents happening, and now we're a lot more cautious."

A Hyundai NEXO fuel cell vehicle with Aurora self-driving systems. Aurora

States don't have clear regulations governing the safety testing and deployment of driverless cars, and that's one challenge to getting them out on the road. As of October, 41 states have either enacted legislation or signed executive orders regulating the testing and use of autonomous vehicles. In September, the National Highway Traffic Safety Administration released new federal guidelines for automated driving systems — but they're only voluntary at this point. Miles driven by test vehicles on real roads had been a frequently touted metric. But to advance the safety of their driverless systems, big players including GM-owned Cruise and Amazon-backed Aurora have also developed their own means of testing in simulation, much like rocket and airplane makers would before a first test flight.

Aurora CEO Chris Urmson Aurora

Aurora CEO and co-founder Chris Urmson explained why this kind of testing matters so much, in addition to real world test driving: "We can create situations that we're basically never going to see or very rarely see. So, for example, we might want to simulate what happens as a bicycle comes through an intersection, runs a red light and crashes into the side of our car. Turns out that doesn't happen very often in the real world, but we want to know that if that happens, our vehicles are going to do something safe ... we're basically allowing the car to practice up in the cloud instead of on the road. And at the end of the day the training that happens online turns into better and better performance offline." A safety-focused culture is essential, said Sam Abuelsamid, principal research analyst at Navigant and an engineer. "When you're testing autonomous vehicles out on public roads, you know, not only are the people riding in that car part of the experiment, but so is everybody else around you. And they didn't consent to being part of an experiment," he said. Dan Albert, an autos historian and author of "Are We There Yet?," said some companies have overstated the benefits of their "self-driving" systems today, and clearer communications about what the technology can and can't do are needed. "One of the things I often hear from people is when an autonomous vehicle is better than the 50th percentile driver on the road, we have an absolute responsibility to let them onto the road," he said. "And others like Elon Musk have said, you know, it's almost irresponsible not to have these vehicles out there because they are safer and will be safer than human drivers ... And so even if we could say that an autonomous vehicle was better than a human driver, it doesn't mean that an autonomous vehicle is better than a human driver plus all the advanced driver assist systems we have."

An employee drives a Tesla Motors Inc. Model S electric automobile, equipped with Autopilot hardware and software, hands-free on a highway. Jasper Juinen | Bloomberg | Getty Images