A report by the county consultant, TranSystems, shows the firm has found “heavy corrosion.” But Woods-Richardson said the county has not neglected the structure’s upkeep.

“We don’t believe that we deferred any maintenance on the bridge,” Woods-Richardson said.

Federal records show that Bear Cut Bridge has been identified as “structurally deficient” since at least 2008. That designation does not necessarily mean the bridge is unsafe, only that it requires repairs or replacement over the next six years.

The steel beams appear to have significantly deteriorated between FDOT’s June 27 inspection and its previous inspection, on June 29, 2010. The state agency inspects bridges every two years, or more frequently if they are in disrepair.

The June 27 inspection report listed a slew of new problems that didn’t exist to such an extent two years earlier, including holes up to six inches wide in “random” locations on the beams. In one photograph, an inspector slips a tape measure through one of the holes. The corrosion in several locations is listed as “severe.”

The latest FDOT quarterly inspection update, released Wednesday, shows the bridge was last inspected on Dec. 26, though the agency has yet to complete its report from that visit.

Several weeks earlier, on Dec. 4, Antonio Cotarelo of the county’s public works department had told the Key Biscayne Village Council that he hoped repairs could begin in six months, after the county identified the scope of the project and hired a firm to carry it out. He estimated the work could last about a year.

The county does not envision replacing the bridge in its entirety, because its foundations appear to be in solid condition. Instead, the public works department intends to replace the steel beams, or girders — there are 584 of them — and the deck, or actual surface, of the bridge that lies on top.

Repairs would likely begin before the county has issued bonds to fund the project, Cotarelo told Key Biscayne. The bonds would be backed by revenues from Rickenbacker Causeway tolls.

The repairs would apply only to the bridge’s westbound lanes. The eastbound lanes were built in 1983, supported by steel beams enclosed in concrete that remain structurally sound. The county would install the same concrete-encased beams in the westbound portion of the bridge.

Between now and then, county and village leaders said they will consider alternatives to the lane closures — particularly for the Sony Open tennis tournament, which draws thousands of spectators to the Crandon Park Tennis Center during two weeks in March. One option: allowing vehicle traffic on the westbound lanes for certain hours on tournament days, for example.

Beyond the tournament, Woods-Richardson also said she is “very, very concerned” about emergency vehicles, such as ambulances and fire-rescue trucks, getting caught in one-lane traffic heading in and out of Key Biscayne, an island with a population of about 13,000.

Police officers directed cars on the bridge early Friday. Cyclists were asked to ride eastbound on a walled-off pathway used by pedestrians and joggers. They were also initially blocked from the westbound bike lane, though access to the lane was later cleared, said Howard Srebnick, a lawyer who rode to Key Biscayne, as he does with a cycling group most mornings, at 6:45 a.m.

He saw several cyclists crash before the westbound bike lane was clearly marked as open for riders, he said. But the eastbound bike lane has been done away with to make room for auto traffic.

“They’ve totally eliminated the bike lane and are diverting all bikes onto a sidewalk that cannot accommodate all that congestion,” Srebnick said.

Still, some cyclists appeared delighted to be given free rein to travel in the westbound bike lane without having to ride next to cars.

One of them, 62-year-old Stuart Solomons, noted that cyclists have been killed riding on the Rickenbacker Causeway — including one struck by a hit-and-run driver on Bear Cut Bridge in 2007.

“Next to guns, drivers are the biggest danger for bicyclists, so anything that makes bicycle lanes safer for us, I’m all for it,” said Solomons, a Key Biscayne resident for the past decade.

Once repairs begin, cycling routes may change, county and village officials warned, asking riders and drivers to be flexible.

“We’re dealing with a situation that requires us to adapt to it,” Caplan said.

Miami Herald staff writers Rene Rodriguez and Andres Viglucci contributed to this report.