With winter approaching, social service providers throughout the city worried that the decision to close the city’s largest homeless shelter would have a major ripple effect on their already strained resources. In recent years, the shelter has housed nearly 600 people on the coldest nights of the year.

It could be as long as five years and cost some $90 million before the 64-year-old bridge is replaced.

City officials were scrambling Thursday to find shelter for more than 400 homeless people and as many as 300 others in recovery programs on Long Island after a state inspection found that an aging two-lane bridge connecting the island in Boston Harbor to the mainland was too dangerous for vehicles to cross.


“This bridge should have been fixed a long time ago,” Mayor Martin J. Walsh said at a news conference outside City Hall on Thursday, noting that city officials had been aware of the bridge’s deteriorating conditions for years.

He vowed to find shelter for those displaced and said it might be possible to ferry people there in the warmer months. The island, which is off North Quincy’s Squantum peninsula, lacks a proper dock for the winter months.

“I’m going to make sure everyone has a place to go,” Walsh said.

The abrupt decision to close the bridge came on Wednesday afternoon, when state inspectors, using new criteria to judge the reliability of bridges, determined that the rusting mass of steel plates, concrete, and rebar was no longer safe, even for the few vehicles allowed to cross. For years, a gate has blocked access to the span, with guards allowing only authorized vehicles, such as the buses that bring an average of 440 homeless people a night onto the island.

Officials at the state Department of Transportation said it appears to make more sense to replace the city-owned bridge, which is known as the Long Island Viaduct and connects to Moon Island. The state has previously offered to share the design costs of replacing the bridge, but Boston will probably have to pay to rebuild it.


Because the bridge is considered a private way and is not on the National Bridge Inventory, federal dollars are unlikely to be available for its replacement.

City officials said the bridge was last inspected sometime between 2010 and 2011. They said it is typically inspected every two years.

State inspectors determined that the rusting bridge was no longer safe — even for the few vehicles that had been authorized to cross it for the past several years. David L Ryan/Globe Staff/Globe Staff

The bridge has been clearly deteriorating over the years — only one vehicle is allowed to cross at a time — but city officials did not expect that it would have to be closed so suddenly.

They said it became urgent to do so because the structural deficiencies mirrored those that caused a bridge over the Mississippi River in Minneapolis to collapse in 2007.

“The environmental impact evaluation, bridge design, and construction may take up to five years, but we are hopeful that the process can be expedited,” said Kate Norton, a spokeswoman for Walsh.

After city officials decided to close the bridge, she said, they activated a plan to maintain all the services provided on the island.

She said the city was still seeking housing and treatment options for everyone on Thursday.

But that was likely to mean more of a burden on other social service agencies throughout the region. In the city’s most recent homeless census, officials last winter counted 7,255 people living on the streets, in shelters, or in special programs, a nearly 4 percent increase over 2013.Of those, 1,367 were in emergency shelters.


John Samaan, president of the Boston Rescue Mission, expects to house more than 60 of the newly displaced people. He said he had been told this summer that the bridge would be closed for repairs for two weeks and that he should be expected to help.

“It’s a shocker that this happened so fast and that it’s a long-term problem,” he said. “I don’t think the system can absorb that many people this fast. It’s going to be a very complicated process.”

Barbara Trevisan, a spokeswoman for the Pine Street Inn, said her shelter is also pitching in. Officials there have already found space for about 80 people in their sobriety programs. Like nearly all shelters in the city, the Pine Street Inn is routinely filled to capacity in the colder months. The homeless sometimes have to sleep on the floor when there are no beds.

“This is certainly a concern for everyone,” she said.

Until the city finds a longer-term solution, Norton said, officials are temporarily housing the displaced at the South End Fitness Center, where they expect to fit as many as 250 people. All fitness programs have been suspended at the facility, which is run by the Boston Public Health Commission.

The city expected to shelter up to 200 people Thursday night at a facility on Albany Street in South Boston, as they worked to increase capacity in the South End.


On Wednesday night, the city used eight facilities to shelter about 415 people.

Each location is being managed by staff from the Public Health Commission, the mayor’s Office of Emergency Management, and the Boston Police Department.

The city is also seeking to find places for those who lost their spots in treatment programs on the island.

“The goal is to place all men and women in long-term recovery programs within 48 hours,” Norton said.

Elvis Perez said he was turned away Wednesday when he sought to catch the bus to Long Island. ESSDRAS M SUAREZ/GLOBE STAFF

Among those stranded this week was Elvis Perez, 49, who was turned away on Wednesday night when he sought to catch the bus to Long Island.

“I don’t know what’s going on,” he said. “It’s like, am I going to sleep in the streets? I don’t know. I’m in shock.”

Robert Everett, 64, said he needs to get back to Long Island to get medication he left in a locker.

“I take them every day,” he said.

Donny Hampton, 54, was on his way to Long Island Wednesday afternoon when his packed bus was stopped just before the bridge.

“Some people were angry; some people were confused; a few were frightened,” he said. “They didn’t know what was going to become of them for the night.”

By 11 p.m., Hampton said, a place was found for him at the Pine Street Inn.

“I ended up sleeping on the dining room floor,” he said. “No mat. No bed or anything. Just on the bare floor with a blanket thrown over me.”


RELATED:

• Bridge closure forces evacuation of hundreds

David Abel can be reached at dabel@globe.com. Follow him on Twitter @davabel.