Mr. Ferguson said there was an opportunity to automate all the trips that Americans make to local stores for goods and services — like buying groceries and picking up laundry — citing statistics that these errands account for a significant portion of all car journeys.

“If we can reduce the cost of these deliveries and get them to you faster than you could make the trip yourself,” he said, “there would be no reason for you to get in the car.”

While that endgame is nowhere close to reality, Mr. Ferguson said it was closer than autonomous passenger services. That’s because Nuro does not have to worry about the comfort and safety of anyone in the vehicle. And by making the delivery automobiles much smaller than a regular car, it can also increase the margin of error on the roads.

“There is a qualitative difference when you don’t have to worry about passengers,” he said.

The trouble is that when testing this technology, Nuro cannot put someone in the mini-vehicle who can take over in case of emergency. So the start-up began by tests in full-size cars. It is now confident enough in its technology to put its tiny vehicles on public roads.

Mr. Ferguson, who often refers to Nuro’s mini cars as rolling toasters, acknowledged that the idea can seem “weird.” But, he said, he ultimately sees them as a safer way of getting autonomous technology rolling.