Designers of futuristic cityscapes envision airborne drones dropping off your packages and driverless cars taking you to work.
But the robotic-delivery invasion already has begun - in the form of machines that look like wheeled beer coolers scooting along the pavements.
The robots - developed by a company with a name straight out of science fiction, Starship Technologies - will be showing up any day in Washington, and in Redwood City, California. They may soon be found in up to 10 US cities, ferrying groceries and other packages from a neighbourhood delivery hub to your front door for as little as US$1 a trip.
A second company, TeleRetail, plans to test its street robots in Washington and other cities this year.
Like driverless cars, the delivery robots use cameras, GPS devices and radar to navigate the urban environment.
The robots are the first of what the companies foresee as a wave of inexpensive, high-tech alternatives to shopping and delivery trips whose cars and trucks contribute to gridlock and pollution. Urban futurists see the vehicles as part of a digitally based "smart city" landscape - although they come with privacy concerns.
"We think there will be hundreds, if not thousands, of robots on the ground eventually around the world," said Allan Martinson, chief operating officer of Starship Technologies, based in London and started by the co-founders of the Internet telephone company Skype.
Torsten Scholl, founder of TeleRetail, based in Switzerland, said: "Why have a vehicle as big as an autonomous car to deliver goods? We think of it as a self-driving trunk."
Tech gadget website Tech Crunch has rated autonomous vehicles - including drones, driverless cars and delivery robots - among the "Top Five Technologies" that will define cities in the next decade.
Starship's robots work this way: Customers use a mobile app to order an item. A text appears - "You have a robot waiting for you outside" - when the robot draws near. A person must be present to receive the delivery because only the customer has a unique code to unlock the robot's box.
"We're excited," said Catherine Ralston, economic development manager of Redwood City, where the robots were given a January start date. "They did a video in our downtown of the robot going into the bakery, picking up baked goods, and at the moment it rolled into City Hall, it popped open and presented the cookies to City Council." They're thinking of using the robots for such city services as delivering library books.
The Washington DC Council opened the door to the machines by passing legislation recently that allows up to five robot companies to operate in the city, though not in the downtown business district.
"To be candid, I'm not at all futuristic. I'm a here-and-now kind of person," said Leif Dormsjo, head of the District's Department of Transportation. "But our approach to transportation innovation is that we want to be a catalyst for new and interesting technologies."
Whether city dwellers will be as enthusiastic as their leaders is open to question.
A year ago, a robot called HitchBOT travelled across Canada, the United Kingdom and the Netherlands before it was brought to the United States. The robot was a social experiment started by two Canadian professors. It looked like a cartoon human and was designed to be picked up on the side of the road voluntarily by drivers, like a hitchhiker.
After just two weeks in the United States, the HitchBOT's world trip ended when it was found dismembered in Philadelphia's historic Old City neighbourhood.
Starship Technologies already has robots operating in 58 cities in 16 countries, Martinson said. More than 1.7 million people have encountered the robots on street pavements or used their services - without incident, he said.
"We took a video in London showing that 3000 people passed by our robots without even noticing them," he said.
Ralston said test units rolling around Redwood City haven't caused any issues so far. "People enjoy seeing the little robots. Or they completely ignore them, they don't even take a glance," she said.
In Northwest Washington recently, a Starship robot drew some attention as it scooted around pedestrians and bicyclists on a busy sidewalk.
Timothy Sanders stopped his bike to watch it weave in and out of human traffic, avoiding pedestrians and cyclists. "It's amazing. It's very futuristic," he said.
But Missy Cummings, director of the Humans and Autonomy Lab at Duke University, worries that new technologies such as drones and sidewalk robots are being developed without enough attention paid to how they will interact with people or to how people will react.
"It's a huge problem in robotics, which are developed by engineers" who know little about human interaction, she said. "Look at Google Glass," she said. The eyeglasses had tiny screens that allowed Internet access, and wearers could take photos and videos using voice commands.
"It wasn't weird to geeky engineers," she said. But real people didn't want to use or wear the glasses - or have their photos taken by people wearing them, she said.
The presence of high-definition video cameras in the robots is a potential privacy issue, too, said Jeramie Scott, director of the Domestic Surveillance Project of the Electronic Privacy Information Centre.
Who controls the images they make, he asks, and how can they be used?
"You can imagine when we get to the place where we have these autonomous drones, on the ground or in the skies flying around, with a lot of surveillance equipment," he said. "We need to understand what is collected and be transparent. We need some kind of oversight in place before the line gets pushed too far."