Common sense says that cars and pedestrians should be kept apart. Pretty straightforward. So why are so many cities challenging that idea? This spring, Chicago will become the latest to do so , as engineers break ground on a $3.5 million street-improvement project to turn a four-block stretch of Argyle Street in the city’s bustling Uptown neighborhood into Chicago’s first shared street—whether residents are ready for it or not.

The idea of shared streets harks back to an older time, when roadways were a free-for-all of pedestrians and horse-drawn vehicles. With the rise of the automobile, however, came automobile fatalities, and with them the idea of separating people into zones: pedestrians on the sidewalk and cars on the street.

When traffic engineer Hans Monderman developed the shared-streets idea in the Netherlands more than 30 years ago, he was going against generations of formal street-design wisdom. Removing signs and signals, he thought, would require both drivers and pedestrians to pay more attention to their environment; in Monderman’s initial pilot, vehicle speeds diminished by 40% on average as a result.

“Naysayers said, ‘People are going to get hit,'” says Patrick Donohue, a project manager with Seattle’s Parks and Recreation department. “Well, it just hasn’t happened.”

“In the traditional system, you see the light is green and then you go, because you trust the system,” explains Pieter de Haan, a psychologist at the University of Applied Sciences in the Netherlands. You gun the engine and don’t even notice the little kid getting away from his mother and running into the street. “Shared space creates a little bit of confusion, which forces you to communicate with others.”

Not surprisingly, many people—including the elderly and the blind—balk at the idea of shared streets. And indeed, nobody is advocating for total chaos. The Argyle Street plan, for instance, uses landscaping and different paver types to delineate areas for pedestrians, bikers, and drivers. Additional “warning pavers” provide tactile information to the blind, using different textures to indicate where pedestrian areas end and vehicle traffic begins. Small, regularly spaced pillars enforce gentle restrictions on both people and cars.