In an emergency move, Miami-Dade will shut down the westbound lanes of the bridge that connects Key Biscayne to Virginia Key, after the state and county found “structural deficiencies” with the decades-old bridge.

Effective Friday morning, the two eastbound lanes of Bear Cut Bridge will be turned into one lane heading toward Key Biscayne and the other lane toward the mainland, the county announced late Thursday after state inspectors raised red flags about the weight of heavy vehicles crossing the structure.

The two westbound lanes will close while the county evaluates and fixes corroded steel beams — a process that could take up to a year, county spokesman Fernando Figueredo said, though he stressed it’s too early to provide a solid timeframe.

The popular Sony Open tennis tournament takes place at the Crandon Park Tennis Center during two weeks in March. Figueredo said the county, in conjunction with the Village of Key Biscayne, is brainstorming about how to alleviate the additional traffic congestion that will be caused by the lane closures during the tournament.

The urgent decision to shut down a portion of the bridge was prompted by recent inspection reports by the Florida Department of Transportation and the county, according to a memo Mayor Carlos Gimenez sent county commissioners late Thursday.

The memo did not provide inspection reports or details of the structural shortcomings, other than to say the problems lie with the Bear Cut Bridge and the West Bridge, located immediately after the Rickenbacker Causeway toll plaza.

“These measures are proactive steps to reduce further deterioration of the bridge in the interest of public safety and are being implemented in consultation with the Village of Key Biscayne,” Gimenez wrote.

Reached late Thursday, Dennis Fernandez, the structures maintenance administrator for FDOT’s Miami district office, said the state agency had recommended that the county impose weight restrictions on heavy vehicles traveling westbound on the bridge.

“The westbound bridge has some capacity left, but not enough to carry the garbage trucks and the emergency vehicles and fuel tankers,” he said.

Key Biscayne issued several vehicle weight restriction alerts via email beginning Dec. 18, including notifying commercial truck drivers on Wednesday that they would be required to obtain county permits to travel on the bridge.

On Thursday, the county decided to allow all vehicles to travel on the bridge — but only on the eastbound lanes.

Key Biscayne Mayor Frank Caplan could not be reached for comment late Thursday.

The problem centers around the bridge’s steel beams, or girders, which have corroded, Fernandez said. The beams support the surface of the bridge where vehicles, cyclists and pedestrians travel.

Previous FDOT inspections had identified the problem, according to Fernandez, who said the issue is limited to the westbound side of the bridge because the eastbound side was more recently renovated. “This is nothing new,” he said.

Because of its problems, FDOT inspects the Bear Cut Bridge more frequently than every two years, as is typical under normal conditions.

The latest FDOT quarterly inspection records, released Wednesday, show Bear Cut Bridge was inspected Dec. 26 and found to be “structurally deficient” — a national rating that indicates the bridge should be replaced or repaired within six years. The bridge has received that rating since at least June 2008, according to Transportation for America, a Washington D.C.-based nonprofit that compiles federal bridge inspection data.