Waymo, which is part of the same company as Google, recently expanded its driverless taxi service in Phoenix — and without a person in the driver’s seat in case something goes wrong. General Motors’ driverless car company will also soon remove human minders from its self-driving test cars in San Francisco. Tesla has said it will soon turn on software features that shift many of its cars on the road into driverless test vehicles.

For now, driverless cars operate in isolated cases. It will be many years before they are reliable, affordable and widespread in all road and weather conditions. And I continue to worry that optimism about driverless cars will make people and policymakers avoid hard choices on inefficient and road clogging transportation and hold out instead for computer-piloted vehicles to solve everything — which they won’t.

But progress is progress. Recent developments point to promise for driverless car technology if we stay realistic about what it can and can’t do. Oliver Cameron, the chief executive of the driverless car company Voyage, said one challenge facing this kind of technology is that people — assuming they aren’t drunk or distracted, which happens too often — are fairly adept at handling circumstances on the road they’ve never seen before. Computers are not. One example Cameron mentioned is the apparently not uncommon problem of a driverless car encountering a flock of wild turkeys.

A human driver might honk or inch forward to try to shoo away the birds, but Cameron says Voyage’s computer system doesn’t know what to do besides freeze in place. “It sounds really simple, but you have to reliably stop or navigate around any and all obstacles,” he told me. There are a zillion other scenarios like this that are individually uncommon but collectively make reliable self-driving cars tricky. And there is little room for error when lives are at stake.

So Voyage is starting “humble,” Cameron said. The company recently revamped its customised computer-piloted taxis to operate without a backup driver, and vehicles operate only in two retirement communities. Low speeds, relatively simple road conditions and a small geography that Voyage computer systems have mapped in advance remove some of the complications and risk. And for seniors, access to door-to-door car service can materially improve their lives.

Even confined to fairly niche cases, Voyage deals with complexities that boggle the mind. The cars have backup systems to the backup systems. Settings prevent riders from grabbing the steering wheel or pressing the gas pedal while the car is in self-driving mode. (We all know people who would do this in a robot-piloted car.) Voyage also has people standing by who can take over cars remotely if they’re needed. I asked Cameron when driverless cars are going to hit the roads in large numbers everywhere. He was hopeful but guardedly so given how driverless car backers have misjudged the technology’s difficulty.

“The optimist in me says things are only going to accelerate from here,” Cameron said. Then he paused and said he couldn’t give me a timeline. “It’s a non-answer,” he said.