Yet beyond the rusty chain links is a newly installed section of eight-foot-high fencing. The shiny metal reflects a fresh flash point in a swiftly changing neighborhood where luxury apartment towers have risen in the last few years.
Last August, Stephen Arthur was riding home to North Park Slope on his bicycle when he was struck in the head by a brick thrown from one of the two ramps onto the footbridge. Though he was wearing a helmet, he crashed, tearing a ligament in his wrist and cutting his face.
Mr. Arthur, a 44-year-old computer programmer, was not the first cyclist on the eight-year-old Navy Street bike path to be hit by objects that youths — for years, residents say — have been throwing from the ramps. But he was the first one to be injured seriously enough to press for something to be done.
In response, the city Transportation Department, with support from local officials, including Community Board 2’s district manager, Robert Perris, and Councilwoman Letitia James, decided to erect additional fencing to extend along the bridge and its ramps. The new fence is curved but open at the top, hanging 18 inches over the walkway, similar to pedestrian passages on the Manhattan and Roosevelt Island Bridges.
The work should be completed this week, according to Transportation Department officials. Already, however, reactions have been wildly divergent, echoing tensions between old and new residents.
“That’s caging us,” said Sharvelle Vinson, 44, who grew up in the Ingersoll Houses. “It’s going too far.”
Valery Jean, the executive director of Families United for Racial and Economic Equality, a community group, said the new fence was a stigmatizing symbol. “On one side of the cage are the people it is protecting, and the other side are the villains,” she said.
Ms. James expressed concern about the scope of the project. “Don’t extend the fence to the point where you send the message to residents that you are not welcome and dangerous,” she said.
Mr. Perris said he recognized “that the solution isn’t perfect, but I looked at it from a public safety standpoint.” If a better remedy were proposed, he said, he would certainly pursue it.
Mr. Arthur said extending the fence to the ramps would protect vulnerable cyclists. “It’s a road safety hazard for anyone, any background,” he said, adding that the issue was not about cyclists versus residents. “This is about senseless violence by youth.”
“If I wasn’t wearing my helmet, forget about it, I would be like Marion Hedges,” he said, referring to a Manhattan real estate broker who was severely injured in October when she was struck by a shopping cart that had been dropped from a walkway of an East Harlem mall.
No one has been arrested in the assault on Mr. Arthur, and there have not been any similar complaints since, the police said. Officers from the 88th Precinct have been posted at the ramps since August, according to Deputy Inspector Kim Royster, a police spokeswoman.
But the police presence, and the city’s swift response, have caused grumbling among some residents.
Ms. Vinson said people had complained to the police about safety issues in the past. “But now you have one person who comes forward and goes ballistic,” she said.
Ed Brown, 47, the president of the Ingersoll Houses tenants’ association, said the fence was a sign of a deeper issue: “The disconnect between newer residents and longtime residents and people coming in the area via the bike lanes.”
“There’s this image of Downtown Brooklyn turning into this great utopia; we’re building diversity,” Mr. Brown said. “But that fence, that right there is detrimental to the whole mission.”
Several Ingersoll tenants said they had heard, wrongly, that the fence would completely cover the footbridge, or that it might be closed entirely.
“At first I heard it was going to be bigger, but I don’t think there’s anything wrong with this,” said Ronald Randolph, 58, as he walked across the bridge on Friday.
Tracy Jones, 35, said: “They needed to put it up. Kids have been throwing things off the bridge since we were young.”
Commenters to articles about what happened to Mr. Arthur seemed to indicate that his experience was not isolated. Yana Walton said children threw small rocks at her about a year and a half ago; she was rattled, but uninjured.
“I glance up now and see if anyone is on the bridge,” said Ms. Walton, 29, of Prospect Heights. She thought that beyond building a fence, there should be a community discussion. “Maybe the parents don’t know what’s going on,” she said.
Ms. Vinson, a mother of five boys, said that engaging restless children was what was needed. “That’s what they need around here, more activities for kids,” she said. “That’s the problem.”