“There are ways of drastically reducing the level of complexity of these systems and making them logical and understandable and reliable,” said Sam Arbesman, the author of Overcomplicated: Technology at the Limits of Comprehension. “The problem is—because of the fact we build the new on top of the old—we aim for these really, really pristine constructions that are built with all these design practices and principles, but things cannot be perfect.”

A more slippery existential problem is that new ways for driverless cars to communicate with pedestrians will only work if people respond to them. But getting people to respond to a new kind of design signal—just getting them to understand it in the first place—is iffy at best.

“People hate ambiguity and unpredictability,” said Chris Rockwell, the CEO and founder of Lextant, a design consulting firm. “I don’t care if it’s your toaster or your car; if you’re confused, you’re not having a great experience. And if it acts in strange or unpredictable ways, it’s not acceptable.”

The trouble is, people are unpredictable. So designing new ways for machines to communicate with them isn’t exactly straightforward. Many ideas for new communications systems have been proposed—driverless cars might feature audible chimes, voice instructions, or text displays to communicate their next moves—but few if any such systems have been tested. “The ideas aren’t the problem; it’s raining ideas,” Rockwell said. “The challenge is really understanding what problem we’re solving. These are human systems, ultimately.”

“From our standpoint, autonomous vehicles and self-driving systems will happen,” he added. “It’s kind of an inevitability. But the challenge won’t be around the technology as much as it will be around the psychology. It’s going to be critical to gain trust—and that trust can be designed into these systems. Trust not only with the passengers, but also the pedestrians outside.”

In an attempt to better understand how pedestrians might respond to self-driving vehicles, roboticists at Duke recently carried an experiment that involved comparing the effectiveness of several different prototypes for vehicle-to-pedestrian communications. (They detailed their findings in a paper that’s now under review for presentation at the Transportation Research Board’s annual meeting.)

The researchers used a van meant to look like a driverless vehicle, and outfitted it with a large display that could feature “walk” and “don’t walk” signals, as well as a numeric display of the speed at which the vehicle was traveling. “The idea was that the participants would use the speedometer to determine whether it was safe to cross,” said Michael Clamann, a roboticist at Duke and one of the lead authors of the paper. “Reading ‘0’ would be the safest, but the objective was to provide a display that would indicate the vehicle was decelerating.”