First there was the High Line, then the Low Line . Now there’s the Green Line: a proposal for a long park that would turn 40 blocks of Broadway, in the middle of Manhattan, into green space.

While the earlier projects focused on transforming unused infrastructure, the new park considers what could happen with roads–which cover a third of the borough’s land–as cars become less popular.

“I think the bigger sort of trajectory is driving is becoming less attractive for people, and more people are walking and biking and taking public transit,” says Jonathan Cohn, principle at Perkins Eastman, the architecture firm that created the renderings. “In general, there’s a lot of interest in making spaces that are more pedestrian-friendly.”

Fewer cars have driven on Broadway since the city closed Times Square and Herald Square to traffic in 2010. The proposed park, which would stretch from Columbus Circle to Union Square, is designed as an extra-long extension of what’s already happening.

“Broadway is changing,” says Cohn. “It’s becoming much more pedestrianized. It’s not an active traffic street anymore for the area that we focused on.”

The designers argue that the park, like the High Line, could bring new business to the neighborhoods nearby, and help raise property values. It could also double as green infrastructure: bioswales, special plantings designed to suck up stormwater, could help suck up rain and snow and keep it from the city’s overloaded sewer system (and, ideally, keep it from dripping into the subway below).

The design, which came out of a fellowship program, is just a concept. But Cohn says there’s no reason it shouldn’t actually happen. “To get anything done in New York is a challenge,” he says. “But we’ve worked on projects of making pedestrian-priority streets already, and people are understanding the benefits of it. … It seems like the natural trajectory for street design now, that we should be doing this.”