Of the hundreds of bridges both big and small in Miami-Dade and Broward counties, only a handful are rated as “structurally deficient” — and engineers say none is in danger of collapsing or being shut down.

But the cost of maintaining, repairing and replacing aging local bridges over the next decade and a half will easily mount into many hundreds of millions of dollars at a time when the state, county and local government agencies responsible for their upkeep face the prospect of tight or shrinking capital funding.

Piecing together the money for even the most crucial repairs is already a constant scramble, highway and public-works engineers say. Their agencies often make millions of dollars worth of repairs to old and obsolete bridges to eke out several more years of use from them, pushing the dreaded date of even costlier full replacement into an uncertain future.

The good news, they say, is that regular bridge inspections carried out by the Florida Department of Transportation mean government engineers have a good handle on maintenance and repair needs, and that surprises like the Rickenbacker Causeway’s Bear Cut Bridge, which had to be partly closed last month after an analysis found unusually rapid structural deterioration, are likely to remain infrequent.

“We’re very proactive to make sure our investment in infrastructure is maintained,” said Gus Pego, FDOT district secretary in Miami.

Still, some of the already-known needs are daunting.

For instance, Miami-Dade public works engineers say they expect to have to replace all 12 bridges, including two drawbridges, on the historic Venetian Causeway, built in the 1920s. The rough cost projection is $110 million, although they are about to embark on a study with FDOT to determine the precise scope and timing of work. Most of the cost, they hope, will be covered by federal grant money.

And that’s after the county spent about $9 million in 2011 to repair spalling and reinforce the concrete pilings supporting some of the Venetian’s bridges.

Dade: $450 million

Miami-Dade, which owns and maintains 206 bridges, roughly projects the cost of rehabilitating or replacing them over the next 10 to 20 years at more than $450 million, though the its engineers caution that the estimate also includes a “wish list” of noncritical work.

Those figures, which include the Venetian, encompass only a portion of the bridges across the county, many of which are owned and maintained by FDOT or municipalities.

Aside from the westbound half of the Bear Cut Bridge, 10 bridges in Miami-Dade are rated by FDOT as structurally deficient, a label that covers a range of issues, including structural deterioration but also some purely functional elements like narrow lanes or inadequate sidewalks.

Bridges on the list include the Miami River drawbridges at Southwest First Street and at Miami Avenue, and the Broad Causeway bridge at that road’s eastern end.

13 Broward spans

In Broward, 13 bridges have the same rating, including the Sunrise Boulevard bridge over the Middle River in Fort Lauderdale.

The details that earn the structurally deficient classification are unavailable because, to protect security, inspection reports are exempt from review under the state’s public-records law.

Each bridge receives a “sufficiency rating” that specifies its overall condition. A sufficiency rating below a certain level means a bridge must be repaired within six years or, in the case of bridges determined to be dangerous, shut down or weight-restricted. None of the Miami-Dade or Broward bridges besides Bear Cut scores at those lowest levels.