About two years ago, I visited the Google X building and took my first ride in one of the search giant's autonomous test vehicles. Looking back, it's astounding how different things were then: Autonomous vehicles were still in a honeymoon period with the public, Tesla had just started selling Full Self Driving as an option, and what is now Waymo was considered one of Google's "moonshots."

It wasn't my first ride in an autonomous vehicle, so my main reaction to the self-driving Lexus RX wasn't the usual first-timer experience of awe at the unbelievable accomplishments of modern technology. Instead, my short ride through Mountain View, Calif., actually gave me a new respect for the human brain. Though surprisingly competent, my robot driver obviously lacked the kind of intuition we humans use heavily in driving and largely take for granted.

For example, driving down a quiet, traffic-free residential street, the vehicle would weave subtly to "avoid" cars parked on either side, as if they might jump out at any moment. This appears to be a problem some autonomous vehicles still face. The 2016 Google car also just generally felt overly cautious, hesitating to accelerate and braking abruptly.

Just a few weeks ago, I found myself back at the Google X building, which has been largely taken over by Waymo. One of Waymo's latest Chrysler Pacificas awaited to take me down the same Mountain View streets I had ridden on before. Everything about it, from the harmonious integration of the company's latest sensor suite to the rider-facing screens and public-friendly interfaces, showed that this was something a lot closer to a polished consumer product.

Out on the road, Waymo's progress was even more obvious compared with two years before. Where the Lexus had driven like a computer with a learner's permit, still not fully convinced of fundamental truths about the road or versed in the art of providing a smooth ride, the Pacifica drove like ... well, a human. Its path planning was noticeably less variable; its acceleration was more assertive; its braking was far smoother. You could watch the houses and traffic go by out the window and almost forget what had been all too obvious two years earlier: that a computer was doing the driving.

Bill Gates famously said that people tend to overestimate what they can do in one year and underestimate what they can do in 10. Back in 2016, most of us radically overestimated what autonomous cars would be able to accomplish over the course of one year, but comparing this year's Waymo Pacifica ride with 2016's Google Lexus RX ride, it's hard not to be impressed with what's been accomplished in two years.

Many tough challenges remain, and many bumps in the road still lie ahead. But I find myself more optimistic today than I would have expected. Though a naturally skeptical person, I somehow feel more awe at the pace of technological progress now than I did the first time I rode in a self-driving car. It's a strange place to be, but it somehow feels right.

-- Edward Niedermeyer