The rating does not necessarily mean that the bridge is unsafe or requires closure; according to Transportation for America, nearly 70,000 bridges — about 11.5 percent — across the United States have been deemed “structurally deficient.”

The latest FDOT records do show a significant drop in the Bear Cut Bridge’s “sufficiency rating,” which considers several factors to determine whether a bridge should be repaired or replaced. That rating dropped to 21 from 66 in its previous inspection, on June 27.

The federal government stepped up bridge inspections after the deadly collapse of a 40-year-old Minneapolis bridge in 2007 put a spotlight on the nation’s aging infrastructure. The Bear Cut Bridge was originally built in 1944 and reconstructed in 1983, according to FDOT records. An average of 30,804 vehicles cross the bridge every day.

The shutdown will also present problems for the thousands of cyclists who ride to Key Biscayne on weekends, and could lead to increased conflicts between automobiles, pedestrians and cyclists who were largely segregated from one another on the eastbound span.

Most cyclists use a wide, designated on-road bike lane, while pedestrians use a walled-off path on the edge of the bridge. Figueredo said one possibility the county is considering is to reroute eastbound cyclists to share the segregated pathway with pedestrians, and to allow cyclists to use the westbound on-road bike lane.

But some cyclists say bikes can’t mix safely with pedestrians and joggers on the narrow path, and they won’t use it.

“It’s impossible,’” said Howard Srebnick, a criminal defense lawyer who rides to Key Biscayne nearly every day with an early-morning cycling group. “That’s a pedestrian walkway.”

Srebnick said his cycling group will use the eastbound car lane to Key Biscayne because it’s safer.

Cyclist Christophe LeCanne was killed by a hit-and-run driver on the bridge in 2010, while riding in the eastbound bike lane.

Miami Herald staff writers Curtis Morgan and Andres Viglucci contributed to this report.