The Northern Avenue Bridge is 110 years old — and it looks its age, with rust-covered beams and grass poking through cracks in the ground-level pavement.

The bridge was closed to cars in 1997 and to pedestrians four years ago, due to fears it might fall into the water. But if its ongoing deterioration makes you melancholy about the passage of time, or the changing face of Boston, think for a moment about what could be here in the near future.

“These ramps come down,” said Emeline Gaujac, a designer at Cambridge’s Prellwitz Chilinski Associates, describing an artist’s rendering of a new, very high-concept Northern Ave. Bridge. “And it would actually be more of a dock-like structure, so it would move with the water.”

Gaujac and several Prellwitz Chilinski colleagues created one of the winning designs in the city of Boston and the Boston Society of Architects' 2016 “ideas competition,” launched to spark interest in the next Northern Ave. Bridge. In their vision, the new structure would let people gather at sea level as traffic passes overhead; turn the old bridgekeeper's house into a waterside café; and be crowned with a greenery-packed urban oasis.

“It’s supposed to be this kind of hidden gem, where you might have these overgrown plants, and you’d get to actually get to look out at the harbor and rest a moment,” Gaujac said.

That, she added, would be a welcome change from the bridges people currently use to cross Fort Point Channel — all of which feature automotive traffic.

“I don’t know if you’ve walked on any of the other bridges, as you’re entering the Seaport or downtown, but it’s not a very pleasant experience,” said Gaujac. “I believe that a lot of people choose not to commute as pedestrians or cyclists because it feels unsafe.”

When they created their design, Gaujac and her colleagues limited its hypothetical use to pedestrians and bikes, with restricted access for emergency and entertainment vehicles. When the real structure actually gets built, however — sometime in the next few years, if all goes according to plan — the balance of use could be very different.

At a recent open house in the Seaport about the planning process for the new bridge, Chris Osgood, Boston’s chief of streets, said plans for how the new structure will look and what types of traffic it will accommodate are still taking shape.

“We’re not yet at the phase where we’re actually showing designs of what the Northern Avenue Bridge may look like in the future,” Osgood said. “That’s really a conversation for 2019."

“On a lot of issues, there’s actually a fair amount of alignment,” he added. “[But] I would say that there’s a lot of unanswered questions around the mobility plan” — in other words, who’ll get to use the bridge and who won’t.

At one point during the open house, which drew a standing-room-only crowd to the Seaport’s District Hall, attendees were told that according to a city traffic study, planners should consider opening the new bridge to high-occupancy vehicles or even general westbound traffic.

Many in the crowd seemed deeply skeptical of that suggestion, including Marc Margulies, who chairs Boston’s Wharf District Council and said traffic in the neighborhood is already nearly intolerable.

“It can take us 45 minutes to get from South Station to Rowes Wharf,” said Margulies.

His fear, Margulies added, is that opening the new Northern Ave. Bridge to automotive traffic will only encourage more people to travel through the neighborhood by cars and trucks, thereby making the problem worse.

While some automotive traffic might be acceptable, Margulies argued, it should be tightly controlled.

“There may be circumstances where during certain times of the day, high-occupancy vehicles of some type might be allowed, but only if it doesn’t change the nature of the bridge and the way it feels,” he said.

But it’s hard to see how it wouldn’t — at least, if the new bridge looks anything like Gaujac’s prototype. And that, in turn, explains her concern about the city’s open-ended approach to the new bridge’s design.

“That space could be exactly what it was — just a bridge with three lanes: locomotives, cars and people,” said Gaujac. “But it wouldn’t be a destination. It wouldn’t represent Boston. It wouldn’t create a place for people."