Boston has dramatically reworked the design for a new Northern Avenue bridge

Don’t expect to drive over the Northern Avenue Bridge ever again.

City officials working on replacing the long-closed bridge over Fort Point Channel appear to be moving toward designing a span that would prioritize walking and bicycling and prohibit single-occupancy cars. Indeed, conceptual images shared Tuesday with an advisory committee don’t show any vehicles.

There are still details to work out before the project can move forward, such as the cost and how to balance the needs of walkers and bikers with those of the corporate shuttle buses used by many people who commute into and out of the Seaport.

But city engineers pledged a “people first” design, and the new images reflect that, depicting two narrow spans crossing the water, connected to a pavilion that extends over the channel.

One span — accommodating one lane of traffic — would be devoted to buses, shuttles, and emergency vehicles. A separate span — on the harbor side — and the space below it would be for walkers and bikers, or just a place for people to congregate.

While the bridge would be planned to “evolve” with the city’s transportation needs, officials said, there are no plans to allow regular car traffic.

“What we heard from the task force, what we heard from the community, is that people want a ‘people first’ experience with the Northern Avenue Bridge,” said Chris Osgood, the city’s chief of streets. “The experience people have both in viewing it and crossing it is what we focused on.”

The concepts, released for the first time Tuesday afternoon, pleasantly surprised advocates who’ve spent years pushing City Hall to rebuild the bridge as a pedestrian-oriented span and not just as another automobile bridge like the nearby Moakley Bridge, which carries Seaport Boulevard over the channel.

“It’s a very, very different place than we were six months ago,” said Stacy Thompson, executive director at the LivableStreets Alliance. “I think this concept is fantastic. . . . There’s a lot to like.”

The plan also reflects other priorities, said Rick Dimino, president of A Better City and chair of a task force that’s advising the city on the bridge, from historic preservation to climate resiliency to creating an interesting new place that better links downtown and the Seaport.

“I’ve got to give the city a lot of credit,” Dimino said. “They found a really interesting way to blend a lot of interests.”

But a lot of questions remain:

How will shuttle buses and pedestrians safely mingle at either end of the bridge, where the two spans would merge?

How much of the Northern Avenue Bridge’s historic architecture would be incorporated into the new structure?

And how will the city pay for it? The Walsh administration has pledged $46 million for the project, but that’s less than half the roughly $100 million that Osgood said will ultimately be needed.

Those issues and others will be worked out as the design process continues, Osgood said. City engineers are aiming for more specific designs by spring, and “100 percent design” in 2021. They would break ground a year after that, and construction would take two to three years.

That means a bridge could open in 2025, a little more than a decade after the original span was closed because of safety concerns.

Tim Logan can be reached at tim.logan@globe.com. Follow him on Twitter at @bytimlogan.